register interest

Dr Antonio Velayos-Baeza

Research Area: Cell and Molecular Biology
Technology Exchange: Microscopy (Confocal)
Scientific Themes: Physiology, Cellular & Molecular Biology and Genetics & Genomics
Keywords: Chorea-Acanthocytosis (ChAc), VPS13A, Dyslexia and KIAA0319
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I am involved in two different research projects, in both cases focused on functional aspects:

  • Chorea-acanthocytosis (ChAc), a rare autosomal-recessive disorder that is characterised by progressive neurodegeneration and red cell acanthocytosis, and
  • Developmental dyslexia, the most common of the childhood learning disorders.

In particular, I work on the functional characterisation of the proteins encoded by the genes VPS13A (mutated in ChAc) and KIAA0319 (associated with dyslexia), as well as on similar human proteins.

Little is known about the function of these proteins. Chorein, encoded by gene VPS13A, is a large protein with no known domains. It presents a vesicular-like pattern when over-expressed in mammalian cell lines. KIAA0319 is a highly glycosylated type I membrane protein which contains five PKD domains, and has been reported to be involved in neuronal migration.

My work focuses on learning as much as possible about the basic properties of these proteins, starting with their characterisation in mammalian cell models. We also use a conditional Knock-out mouse model for the KIAA0319-homologous gene to investigate the effects that the deletion of this gene has in mouse brain development.

Name Department Institution Country
Professor Zoltan Molnar Physiology, Anatomy and Genetics University of Oxford United Kingdom
Professor Adrian Danek Neurologische Klinik Ludwig-Maximilians-Universität (Munich) Germany
Dr Simon E Fisher Wellcome Trust Centre for Human Genetics Oxford University, Henry Wellcome Building of Genomic Medicine United Kingdom
Professor Joseph J LoTurco Physiology and Neurobiology University of Connecticut United States
Franquinho F, Nogueira-Rodrigues J, Duarte JM, Esteves SS, Carter-Su C, Monaco AP, Molnár Z, Velayos-Baeza A, Brites P, Sousa MM. 2017. The Dyslexia-susceptibility Protein KIAA0319 Inhibits Axon Growth Through Smad2 Signaling. Cereb Cortex, 27 (3), pp. 1732-1747. | Show Abstract | Read more

KIAA0319 is a transmembrane protein associated with dyslexia with a presumed role in neuronal migration. Here we show that KIAA0319 expression is not restricted to the brain but also occurs in sensory and spinal cord neurons, increasing from early postnatal stages to adulthood and being downregulated by injury. This suggested that KIAA0319 participates in functions unrelated to neuronal migration. Supporting this hypothesis, overexpression of KIAA0319 repressed axon growth in hippocampal and dorsal root ganglia neurons; the intracellular domain of KIAA0319 was sufficient to elicit this effect. A similar inhibitory effect was observed in vivo as axon regeneration was impaired after transduction of sensory neurons with KIAA0319. Conversely, the deletion of Kiaa0319 in neurons increased neurite outgrowth in vitro and improved axon regeneration in vivo. At the mechanistic level, KIAA0319 engaged the JAK2-SH2B1 pathway to activate Smad2, which played a central role in KIAA0319-mediated repression of axon growth. In summary, we establish KIAA0319 as a novel player in axon growth and regeneration with the ability to repress the intrinsic growth potential of axons. This study describes a novel regulatory mechanism operating during peripheral nervous system and central nervous system axon growth, and offers novel targets for the development of effective therapies to promote axon regeneration.

Vonk JJ, Yeshaw WM, Pinto F, Faber AIE, Lahaye LL, Kanon B, van der Zwaag M, Velayos-Baeza A, Freire R, van IJzendoorn SC et al. 2017. Drosophila Vps13 Is Required for Protein Homeostasis in the Brain. PLoS One, 12 (1), pp. e0170106. | Show Abstract | Read more

Chorea-Acanthocytosis is a rare, neurodegenerative disorder characterized by progressive loss of locomotor and cognitive function. It is caused by loss of function mutations in the Vacuolar Protein Sorting 13A (VPS13A) gene, which is conserved from yeast to human. The consequences of VPS13A dysfunction in the nervous system are still largely unspecified. In order to study the consequences of VPS13A protein dysfunction in the ageing central nervous system we characterized a Drosophila melanogaster Vps13 mutant line. The Drosophila Vps13 gene encoded a protein of similar size as human VPS13A. Our data suggest that Vps13 is a peripheral membrane protein located to endosomal membranes and enriched in the fly head. Vps13 mutant flies showed a shortened life span and age associated neurodegeneration. Vps13 mutant flies were sensitive to proteotoxic stress and accumulated ubiquitylated proteins. Levels of Ref(2)P, the Drosophila orthologue of p62, were increased and protein aggregates accumulated in the central nervous system. Overexpression of the human Vps13A protein in the mutant flies partly rescued apparent phenotypes. This suggests a functional conservation of human VPS13A and Drosophila Vps13. Our results demonstrate that Vps13 is essential to maintain protein homeostasis in the larval and adult Drosophila brain. Drosophila Vps13 mutants are suitable to investigate the function of Vps13 in the brain, to identify genetic enhancers and suppressors and to screen for potential therapeutic targets for Chorea-Acanthocytosis.

Velayos-Baeza A, Danek A. 2017. Chorein Deficiency and Alzheimer Disease: An Intriguing, Yet Premature Speculation. Alzheimer Dis Assoc Disord, 31 (1), pp. 80-81. | Read more

Martinez-Garay I, Guidi LG, Holloway ZG, Bailey MAG, Lyngholm D, Schneider T, Donnison T, Butt SJB, Monaco AP, Molnár Z, Velayos-Baeza A. 2017. Normal radial migration and lamination are maintained in dyslexia-susceptibility candidate gene homolog Kiaa0319 knockout mice. Brain Struct Funct, 222 (3), pp. 1367-1384. | Show Abstract | Read more

Developmental dyslexia is a common disorder with a strong genetic component, but the underlying molecular mechanisms are still unknown. Several candidate dyslexia-susceptibility genes, including KIAA0319, DYX1C1, and DCDC2, have been identified in humans. RNA interference experiments targeting these genes in rat embryos have shown impairments in neuronal migration, suggesting that defects in radial cortical migration could be involved in the disease mechanism of dyslexia. Here we present the first characterisation of a Kiaa0319 knockout mouse line. Animals lacking KIAA0319 protein do not show anatomical abnormalities in any of the layered structures of the brain. Neurogenesis and radial migration of cortical projection neurons are not altered, and the intrinsic electrophysiological properties of Kiaa0319-deficient neurons do not differ from those of wild-type neurons. Kiaa0319 overexpression in cortex delays radial migration, but does not affect final neuronal position. However, knockout animals show subtle differences suggesting possible alterations in anxiety-related behaviour and in sensorimotor gating. Our results do not reveal a migration disorder in the mouse model, adding to the body of evidence available for Dcdc2 and Dyx1c1 that, unlike in the rat in utero knockdown models, the dyslexia-susceptibility candidate mouse homolog genes do not play an evident role in neuronal migration. However, KIAA0319 protein expression seems to be restricted to the brain, not only in early developmental stages but also in adult mice, indicative of a role of this protein in brain function. The constitutive and conditional knockout lines reported here will be useful tools for further functional analyses of Kiaa0319.

Mehta ZB, Fine N, Pullen TJ, Cane MC, Hu M, Chabosseau P, Meur G, Velayos-Baeza A, Monaco AP, Marselli L et al. 2016. Changes in the expression of the type 2 diabetes-associated gene VPS13C in the β-cell are associated with glucose intolerance in humans and mice. Am J Physiol Endocrinol Metab, 311 (2), pp. E488-E507. | Show Abstract | Read more

Single nucleotide polymorphisms (SNPs) close to the VPS13C, C2CD4A and C2CD4B genes on chromosome 15q are associated with impaired fasting glucose and increased risk of type 2 diabetes. eQTL analysis revealed an association between possession of risk (C) alleles at a previously implicated causal SNP, rs7163757, and lowered VPS13C and C2CD4A levels in islets from female (n = 40, P < 0.041) but not from male subjects. Explored using promoter-reporter assays in β-cells and other cell lines, the risk variant at rs7163757 lowered enhancer activity. Mice deleted for Vps13c selectively in the β-cell were generated by crossing animals bearing a floxed allele at exon 1 to mice expressing Cre recombinase under Ins1 promoter control (Ins1Cre). Whereas Vps13c(fl/fl):Ins1Cre (βVps13cKO) mice displayed normal weight gain compared with control littermates, deletion of Vps13c had little effect on glucose tolerance. Pancreatic histology revealed no significant change in β-cell mass in KO mice vs. controls, and glucose-stimulated insulin secretion from isolated islets was not altered in vitro between control and βVps13cKO mice. However, a tendency was observed in female null mice for lower insulin levels and β-cell function (HOMA-B) in vivo. Furthermore, glucose-stimulated increases in intracellular free Ca(2+) were significantly increased in islets from female KO mice, suggesting impaired Ca(2+) sensitivity of the secretory machinery. The present data thus provide evidence for a limited role for changes in VPS13C expression in conferring altered disease risk at this locus, particularly in females, and suggest that C2CD4A may also be involved.

Yang R-Y, Xue H, Yu L, Velayos-Baeza A, Monaco AP, Liu F-T. 2016. Identification of VPS13C as a Galectin-12-Binding Protein That Regulates Galectin-12 Protein Stability and Adipogenesis. PLoS One, 11 (4), pp. e0153534. | Show Abstract | Read more

Galectin-12, a member of the galectin family of β-galactoside-binding animal lectins, is preferentially expressed in adipocytes and required for adipocyte differentiation in vitro. This protein was recently found to regulate lipolysis, whole body adiposity, and glucose homeostasis in vivo. Here we identify VPS13C, a member of the VPS13 family of vacuolar protein sorting-associated proteins highly conserved throughout eukaryotic evolution, as a major galectin-12-binding protein. VPS13C is upregulated during adipocyte differentiation, and is required for galectin-12 protein stability. Knockdown of Vps13c markedly reduces the steady-state levels of galectin-12 by promoting its degradation through primarily the lysosomal pathway, and impairs adipocyte differentiation. Our studies also suggest that VPS13C may have a broader role in protein quality control. The regulation of galectin-12 stability by VPS13C could potentially be exploited for therapeutic intervention of obesity and related metabolic diseases.

Nagy A, Noyce A, Velayos-Baeza A, Lees AJ, Warner TT, Ling H. 2015. Late Emergence of Parkinsonian Phenotype and Abnormal Dopamine Transporter Scan in Chorea-Acanthocytosis Movement Disorders Clinical Practice, 2 (2), pp. 182-186. | Read more

Holloway ZG, Velayos-Baeza A, Howell GJ, Levecque C, Ponnambalam S, Sztul E, Monaco AP. 2013. Trafficking of the Menkes copper transporter ATP7A is regulated by clathrin-, AP-2-, AP-1-, and Rab22-dependent steps. Mol Biol Cell, 24 (11), pp. 1735-S8. | Show Abstract | Read more

The transporter ATP7A mediates systemic copper absorption and provides cuproenzymes in the trans-Golgi network (TGN) with copper. To regulate metal homeostasis, ATP7A constitutively cycles between the TGN and plasma membrane (PM). ATP7A trafficking to the PM is elevated in response to increased copper load and is reversed when copper concentrations are lowered. Molecular mechanisms underlying this trafficking are poorly understood. We assess the role of clathrin, adaptor complexes, lipid rafts, and Rab22a in an attempt to decipher the regulatory proteins involved in ATP7A cycling. While RNA interference (RNAi)-mediated depletion of caveolin 1/2 or flotillin had no effect on ATP7A localization, clathrin heavy chain depletion or expression of AP180 dominant-negative mutant not only disrupted clathrin-regulated pathways, but also blocked PM-to-TGN internalization of ATP7A. Depletion of the μ subunits of either adaptor protein-2 (AP-2) or AP-1 using RNAi further provides evidence that both clathrin adaptors are important for trafficking of ATP7A from the PM to the TGN. Expression of the GTP-locked Rab22aQ64L mutant caused fragmentation of TGN membrane domains enriched for ATP7A. These appear to be a subdomain of the mammalian TGN, showing only partial overlap with the TGN marker golgin-97. Of importance, ATP7A remained in the Rab22aQ64L-generated structures after copper treatment and washout, suggesting that forward trafficking out of this compartment was blocked. This study provides evidence that multiple membrane-associated factors, including clathrin, AP-2, AP-1, and Rab22, are regulators of ATP7A trafficking.

Walker RH, Velayos-Baeza A, Bader B, Danek A, Saiki S. 2012. Mutation in the CHAC gene in a family of autosomal dominant chorea-acanthocytosis. Neurology, 79 (2), pp. 198-199. | Read more

Danek A, Bader B, Velayos-Baeza A, Walker RH. 2012. Autosomal recessive transmission of chorea-acanthocytosis confirmed. Acta Neuropathol, 123 (6), pp. 905-906. | Read more

Velayos-Baeza A, Holinski-Feder E, Neitzel B, Bader B, Critchley EMR, Monaco AP, Danek A, Walker RH. 2011. Chorea-acanthocytosis genotype in the original critchley kentucky neuroacanthocytosis kindred. Arch Neurol, 68 (10), pp. 1330-1333. | Show Abstract | Read more

OBJECTIVE: To determine the molecular nature of the neurological disease in the seminal family reported by Critchley et al in the 1960s, characterized by a hyperkinetic movement disorder and the appearance of acanthocytosis on peripheral blood smear. The eponym Levine-Critchley syndrome, subsequently termed neuroacanthocytosis, has been applied to symptomatically similar, but genetically distinct, disorders, resulting in clinical and diagnostic confusion. DESIGN: DNA analysis. SETTING: Molecular biology research laboratories. PARTICIPANTS: First- and second-degree relatives of the original Critchley et al proband from Kentucky. MAIN OUTCOME MEASURES: Mutations in the VPS13A gene. RESULTS: A mutation was identified in the VPS13A gene, responsible for autosomal recessive chorea-acanthocytosis. Haplotype reconstruction suggested that this mutation was homozygous in the proband. CONCLUSION: These findings strongly support the diagnosis of chorea-acanthocytosis as the disorder described in the original report.

Sanz C, Velayos A, Álvarez MI, Benito EP, Eslava AP. 2011. Functional analysis of the Phycomyces carRA gene encoding the enzymes phytoene synthase and lycopene cyclase. PLoS One, 6 (8), pp. e23102. | Show Abstract | Read more

Phycomyces carRA gene encodes a protein with two domains. Domain R is characterized by red carR mutants that accumulate lycopene. Domain A is characterized by white carA mutants that do not accumulate significant amounts of carotenoids. The carRA-encoded protein was identified as the lycopene cyclase and phytoene synthase enzyme by sequence homology with other proteins. However, no direct data showing the function of this protein have been reported so far. Different Mucor circinelloides mutants altered at the phytoene synthase, the lycopene cyclase or both activities were transformed with the Phycomyces carRA gene. Fully transcribed carRA mRNA molecules were detected by Northern assays in the transformants and the correct processing of the carRA messenger was verified by RT-PCR. These results showed that Phycomyces carRA gene was correctly expressed in Mucor. Carotenoids analysis in these transformants showed the presence of ß-carotene, absent in the untransformed strains, providing functional evidence that the Phycomyces carRA gene complements the M. circinelloides mutations. Co-transformation of the carRA cDNA in E. coli with different combinations of the carotenoid structural genes from Erwinia uredovora was also performed. Newly formed carotenoids were accumulated showing that the Phycomyces CarRA protein does contain lycopene cyclase and phytoene synthase activities. The heterologous expression of the carRA gene and the functional complementation of the mentioned activities are not very efficient in E. coli. However, the simultaneous presence of both carRA and carB gene products from Phycomyces increases the efficiency of these enzymes, presumably due to an interaction mechanism.

Velayos-Baeza A, Levecque C, Kobayashi K, Holloway ZG, Monaco AP. 2010. The dyslexia-associated KIAA0319 protein undergoes proteolytic processing with {gamma}-secretase-independent intramembrane cleavage. J Biol Chem, 285 (51), pp. 40148-40162. | Show Abstract | Read more

The KIAA0319 gene has been associated with reading disability in several studies. It encodes a plasma membrane protein with a large, highly glycosylated, extracellular domain. This protein is proposed to function in adhesion and attachment and thought to play an important role during neuronal migration in the developing brain. We have previously proposed that endocytosis of this protein could constitute an important mechanism to regulate its function. Here we show that KIAA0319 undergoes ectodomain shedding and intramembrane cleavage. At least five different cleavage events occur, four in the extracellular domain and one within the transmembrane domain. The ectodomain shedding processing cleaves the extracellular domain, generating several small fragments, including the N-terminal region with the Cys-rich MANEC domain. It is possible that these fragments are released to the extracellular medium and trigger cellular responses. The intramembrane cleavage releases the intracellular domain from its membrane attachment. Our results suggest that this cleavage event is not carried out by γ-secretase, the enzyme complex involved in similar processing in many other type I proteins. The soluble cytoplasmic domain of KIAA0319 is able to translocate to the nucleus, accumulating in nucleoli after overexpression. This fragment has an unknown role, although it could be involved in regulation of gene expression. The absence of DNA-interacting motifs indicates that such a function would most probably be mediated through interaction with other proteins, not by direct DNA binding. These results suggest that KIAA0319 not only has a direct role in neuronal migration but may also have additional signaling functions.

Levecque C, Velayos-Baeza A, Holloway ZG, Monaco AP. 2009. The dyslexia-associated protein KIAA0319 interacts with adaptor protein 2 and follows the classical clathrin-mediated endocytosis pathway. Am J Physiol Cell Physiol, 297 (1), pp. C160-C168. | Show Abstract | Read more

Recently, genetic studies have implicated KIAA0319 in developmental dyslexia, the most common of the childhood learning disorders. The first functional data indicated that the KIAA0319 protein is expressed on the plasma membrane and may be involved in neuronal migration. Further analysis of the subcellular distribution of the overexpressed protein in mammalian cells indicates that KIAA0319 can colocalize with the early endosomal marker early endosome antigen 1 (EEA1) in large intracellular vesicles, suggesting that it is endocytosed. Antibody internalization assays with full-length KIAA0319 and deletion constructs confirmed that KIAA0319 is internalized and showed the importance of the cytoplasmic juxtamembranal region in this process. The present study has identified the medium subunit (mu2) of adaptor protein 2 (AP-2) as a binding partner of KIAA0319 in a yeast two-hybrid screen. Using Rab5 mutants or depletion of the mu-subunit of AP-2 or clathrin heavy chain by RNA interference, we demonstrate that KIAA0319 follows a clathrin-mediated endocytic pathway. We also identify tyrosine-995 of KIAA0319 as a critical amino acid required for the interaction with AP-2 and subsequent internalization. These results suggest the surface expression of KIAA0319 is regulated by endocytosis, supporting the idea that the internalization and recycling of the protein may be involved in fine tuning its role in neuronal migration.

Bader B, Velayos-Baeza A, Walker RH, Danek A. 2009. Dominant transmission of chorea-acanthocytosis with VPS13A mutations remains speculative. Acta Neuropathol, 117 (1), pp. 95-96. | Read more

Velayos-Baeza A, Toma C, Paracchini S, Monaco AP. 2008. The dyslexia-associated gene KIAA0319 encodes highly N- and O-glycosylated plasma membrane and secreted isoforms. Hum Mol Genet, 17 (6), pp. 859-871. | Show Abstract | Read more

The KIAA0319 gene has been recently associated with developmental dyslexia and shown to be involved in neuronal migration. The deduced KIAA0319 protein contains several polycystic kidney disease (PKD) domains which may mediate the interaction between neurons and glial fibres during neuronal migration. We have previously reported the presence of several alternative splicing variants, some of which are predicted to affect the deduced protein. In this study, we over-expressed constructs containing the main form (A) and two alternative variants (B and C) of KIAA0319. We show that the full-length KIAA0319 (A) is a type I plasma membrane protein, a topology consistent with its proposed function in neuronal migration. The oligomeric status of KIAA0319 is mainly dimeric, and this condition depends on the cysteine-rich regions of the protein, especially the transmembrane (TM) domain and surrounding sequence. KIAA0319 is highly glycosylated in different mammalian cell lines. The central region including the PKD domains is N-glycosylated. Furthermore, a short fragment N-terminal to the PKD domains contains mucin-type O-glycosylation. The two alternative isoforms are soluble proteins lacking the TM domain and, interestingly, only isoform B is secreted. KIAA0319-deletion proteins lacking the TM domain were also secreted. These results suggest that KIAA0319 could be involved not only in cell-cell interactions, but also in signalling.

Francks C, Maegawa S, Laurén J, Abrahams BS, Velayos-Baeza A, Medland SE, Colella S, Groszer M, McAuley EZ, Caffrey TM et al. 2007. LRRTM1 on chromosome 2p12 is a maternally suppressed gene that is associated paternally with handedness and schizophrenia. Mol Psychiatry, 12 (12), pp. 1129-1057. | Show Abstract | Read more

Left-right asymmetrical brain function underlies much of human cognition, behavior and emotion. Abnormalities of cerebral asymmetry are associated with schizophrenia and other neuropsychiatric disorders. The molecular, developmental and evolutionary origins of human brain asymmetry are unknown. We found significant association of a haplotype upstream of the gene LRRTM1 (Leucine-rich repeat transmembrane neuronal 1) with a quantitative measure of human handedness in a set of dyslexic siblings, when the haplotype was inherited paternally (P=0.00002). While we were unable to find this effect in an epidemiological set of twin-based sibships, we did find that the same haplotype is overtransmitted paternally to individuals with schizophrenia/schizoaffective disorder in a study of 1002 affected families (P=0.0014). We then found direct confirmatory evidence that LRRTM1 is an imprinted gene in humans that shows a variable pattern of maternal downregulation. We also showed that LRRTM1 is expressed during the development of specific forebrain structures, and thus could influence neuronal differentiation and connectivity. This is the first potential genetic influence on human handedness to be identified, and the first putative genetic effect on variability in human brain asymmetry. LRRTM1 is a candidate gene for involvement in several common neurodevelopmental disorders, and may have played a role in human cognitive and behavioral evolution.

Velayos-Baeza A, Toma C, da Roza S, Paracchini S, Monaco AP. 2007. Alternative splicing in the dyslexia-associated gene KIAA0319. Mamm Genome, 18 (9), pp. 627-634. | Show Abstract | Read more

The KIAA0319 gene in chromosome 6p22 has been strongly associated with developmental dyslexia. In this article we show a wide expression pattern of this gene in human adult brain by Northern blot analysis. We also performed RT-PCR analysis to detect alternative splicing variants in human brain. Most of the detected variants involve alternative splicing of the exons at the 5' and the 3' ends. Two main forms differing in the length of the 5' UTR are detected at approximately the same rate. Two variants (B and C) lacking exon 19, which encodes the transmembrane domain, are the main alternative forms detected among those predicted to encode protein. These two variants could be secreted and might be involved in signaling functions. A similar RT-PCR analysis performed in mouse and rat adult brains showed that only some of the alternative splicing variants are equivalent to those found in the human gene.

Francks C, Maegawa S, Laurén J, Abrahams BS, Velayos-Baeza A, Medland SE, Colella S, Groszer M, McAuley EZ, Caffrey TM et al. 2007. LRRTM1 protein is located in the endoplasmic reticulum (ER) in mammalian cells Molecular Psychiatry, 12 (12), pp. 1057-1057. | Read more

Papp T, Velayos A, Bartók T, Eslava AP, Vágvölgyi C, Iturriaga EA. 2006. Heterologous expression of astaxanthin biosynthesis genes in Mucor circinelloides. Appl Microbiol Biotechnol, 69 (5), pp. 526-531. | Show Abstract | Read more

Most Mucor species accumulate beta-carotene as the main carotenoid. The crtW and crtZ astaxanthin biosynthesis genes from Agrobacterium aurantiacum were placed under the control of Mucor circinelloides expression signals. Expression vectors containing the bacterial genes were constructed, and PEG-mediated transformations were performed on a selected M. circinelloides strain. Transformants that exhibited altered carotene production were isolated and analyzed. Southern analysis showed that all plasmids behave as autoreplicative elements. Northern analysis detected the actual heterologous transcription products, whereas thin layer chromatography and high-performance liquid chromatography studies revealed the presence of new carotenoid compounds and intermediates among the transformants.

Dobson-Stone C, Velayos-Baeza A, Jansen A, Andermann F, Dubeau F, Robert F, Summers A, Lang AE, Chouinard S, Danek A et al. 2005. Identification of a VPS13A founder mutation in French Canadian families with chorea-acanthocytosis. Neurogenetics, 6 (3), pp. 151-158. | Show Abstract | Read more

Mutations in VPS13A cause chorea-acanthocytosis (ChAc), an autosomal recessive neurodegenerative disorder. VPS13A is located in a tail-to-tail arrangement with GNA14 on chromosome 9q21. ChAc shows substantial allelic heterogeneity, with no single VPS13A mutation causing the majority of cases. We examined 11 patients in four French Canadian ChAc pedigrees for mutations in VPS13A. Affected members of three families were homozygous for a 37-kb deletion of the four terminal exons of VPS13A (EX70_EX73del). This deletion also encompasses the two terminal exons of GNA14. Two affected females in family 4 were homozygous for the splicing mutation 4242+1G>T. Remarkably, the affected males in this highly consanguineous pedigree were compound heterozygotes for EX70_EX73del and 4242+1G>T. PCR analysis of the deletion breakpoint junction revealed that an additional patient with French Canadian ancestry was heterozygous for the EX70_EX73del allele. The identification of a common 9q21 haplotype associated with EX70_EX73del in at least four apparently unrelated ChAc families implies that ChAc shows a founder effect in French Canadians, and that routine testing for EX70_EX73del in suspected ChAc cases may therefore be worthwhile in this population. The deletion breakpoint PCR described here will enable rapid identification of both homozygous and heterozygous carriers of EX70_EX73del.

Velayos-Baeza A, Vettori A, Copley RR, Dobson-Stone C, Monaco AP. 2004. Analysis of the human VPS13 gene family. Genomics, 84 (3), pp. 536-549. | Show Abstract | Read more

The gene mutated in chorea-acanthocytosis (CHAC; approved gene symbol VPS13A) encodes chorein, a protein similar to yeast Vps13p. We detected several similar putative human proteins by BLAST analysis of chorein. We characterized the structure of three new genes encoding these CHAC-similar proteins, located on chromosomes 1p36, 8q22, and 15q21. The most similar gene in yeast to all four human genes is Vps13, and therefore the human genes were named VPS13A (CHAC, 9q21), VPS13B (8q22), VPS13C (15q21), and VPS13D (1p36). VPS13B has recently been reported as COH1, altered in Cohen syndrome. For each gene, we describe several alternative splicing variants; at least two transcripts per gene are major forms. The expression pattern of these genes is ubiquitous, with some tissue-specific differences between several transcript variants. Protein sequence comparisons suggest that intramolecular duplications have played an important role in the evolution of this gene family.

Dobson-Stone C, Velayos-Baeza A, Filippone LA, Westbury S, Storch A, Erdmann T, Wroe SJ, Leenders KL, Lang AE, Dotti MT et al. 2004. Chorein detection for the diagnosis of chorea-acanthocytosis. Ann Neurol, 56 (2), pp. 299-302. | Show Abstract | Read more

Chorea-acanthocytosis (ChAc) is a severe, neurodegenerative disorder that shares clinical features with Huntington's disease and McLeod syndrome. It is caused by mutations in VPS13A, which encodes a large protein called chorein. Using antichorein antisera, we found expression of chorein in all human cells analyzed. However, chorein expression was absent or noticeably reduced in ChAc patient cells, but not McLeod syndrome and Huntington's disease cells. This suggests that loss of chorein expression is a diagnostic feature of ChAc.

Velayos A, Fuentes-Vicente M, Aguilar-Elena R, Eslava AP, Iturriaga EA. 2004. A novel fungal prenyl diphosphate synthase in the dimorphic zygomycete Mucor circinelloides. Curr Genet, 45 (6), pp. 371-377. | Show Abstract | Read more

Two Mucor circinelloides structural genes involved in isoprenoid biosynthesis were isolated and characterised. The isoA gene encodes a typical eukaryotic farnesyl diphosphate synthase (EC 2.5.1.10), whereas the isoB gene deduced amino acid sequence shows similarity to fungal medium-chain prenyl diphosphate synthases. By functional complementation in Escherichia coli, the isoB gene product was shown to be a solanesyl diphosphate synthase (EC 2.5.1.11), which is the first fungal enzyme reported having this specificity. In addition, a M. circinelloides one-marker-per-chromosome map was completed by contour-clamped homogeneous electric field localisation of isoA, isoB and three other isoprenoid biosynthesis genes to individual chromosomes.

Velayos A, Papp T, Aguilar-Elena R, Fuentes-Vicente M, Eslava AP, Iturriaga EA, Alvarez MI. 2003. Expression of the carG gene, encoding geranylgeranyl pyrophosphate synthase, is up-regulated by blue light in Mucor circinelloides. Curr Genet, 43 (2), pp. 112-120. | Show Abstract | Read more

A new structural gene, carG, involved in the biosynthesis of carotenoids in the fungus Mucor circinelloides was isolated by heterologous hybridisation, using a probe derived from the Gibberella fujikuroi ggs1 gene. Functional analyses in Escherichia coli showed that the encoded protein has geranylgeranyl pyrophosphate (GGPP) synthase activity. A comparison of the deduced protein with other GGPP synthases suggested that the carG gene might have evolved from other larger genes present in some fungi. The analysis of carG mRNA accumulation after blue light irradiation showed that the expression of this gene is up-regulated by blue light, as happens with the other structural genes involved in carotenogenesis in M. circinelloides. Analysis of the promoter region revealed the presence of several APE-like sequences, which participate in the blue-light regulation of the expression of different fungal genes. These sequences are also present in the above-mentioned Mucor genes and strongly support the idea that this gene plays an important role in the regulation of carotenoid synthesis, despite belonging to a more general metabolic pathway.

Sanz C, Alvarez MI, Orejas M, Velayos A, Eslava AP, Benito EP. 2002. Interallelic complementation provides genetic evidence for the multimeric organization of the Phycomyces blakesleeanus phytoene dehydrogenase. Eur J Biochem, 269 (3), pp. 902-908. | Show Abstract | Read more

The Phycomyces blakesleeanus wild-type is yellow, because it accumulates beta-carotene as the main carotenoid. A new carotenoid mutant of this fungus (A486) was isolated, after treatment with ethyl methane sulfonate (EMS), showing a whitish coloration. It accumulates large amounts of phytoene, small quantities of phytofluene, zeta-carotene and neurosporene, in decreasing amounts, and traces of beta-carotene. This phenotype indicates that it carries a leaky mutation affecting the enzyme phytoene dehydrogenase (EC 1.3.-.-), which is specified by the gene carB. Biochemical analysis of heterokaryons showed that mutant A486 complements two previously characterized carB mutants, C5 (carB10) and S442 (carB401). Sequence analysis of the carB gene genomic copy from these three strains revealed that they are all altered in the gene carB, giving information about the nature of the mutation in each carB mutant allele. The interallelic complementation provides evidence for the multimeric organization of the P. blakesleeanus phytoene dehydrogenase.

Velayos A, Eslava AP, Iturriaga EA. 2000. A bifunctional enzyme with lycopene cyclase and phytoene synthase activities is encoded by the carRP gene of Mucor circinelloides. Eur J Biochem, 267 (17), pp. 5509-5519. | Show Abstract | Read more

Using functional analyses in Escherichia coli and Mucor circinelloides, it has been shown that a single M. circinelloides gene (carRP) codes for a protein with two different enzymatic activities, lycopene cyclase and phytoene synthase, which are encoded by independent genes in organisms other than fungi. This gene was identified using complementation tests among different classes of carotenoid mutants of M. circinelloides. The carRP gene product contains two domains: the R domain is located at the N-terminus and determines lycopene cyclase activity; the P domain is located at the C-terminus and displays phytoene synthase activity. The R domain is functional even in the absence of the P domain, while the latter needs the proper R domain conformation to carry out its function. The carRP gene is closely linked to the phytoene dehydrogenase (carB) gene, and the promoter regions of both genes are located within only 446 bp. Northern analyses show a co-ordinated regulation of the expression of both genes by blue light. Several motifs found in this promoter region suggest a bi-directional mode of transcription control.

Velayos A, Blasco JL, Alvarez MI, Iturriaga EA, Eslava AP. 2000. Blue-light regulation of phytoene dehydrogenase (carB) gene expression in Mucor circinelloides. Planta, 210 (6), pp. 938-946. | Show Abstract | Read more

The carB gene, encoding the phytoene dehydrogenase of Mucor circinelloides, was isolated by heterologous hybridisation with a probe derived from the corresponding gene of Phycomyces blakesleeanus. The cDNA and genomic copies complemented phytoene dehydrogenase defects in Escherichia coli and in carB mutants of M. circinelloides, respectively. Fluence-response curves for transcript accumulation were constructed after different blue-light pulses. The level of carB mRNA accumulation reached values up to 150-fold higher than basal levels in darkness. Several elements in the promoter of this gene resemble a consensus sequence identified in Neurospora crassa (APE) which is essential for blue-light regulation. Comparison of the available phytoene dehydrogenase sequences from plants, fungi, algae and bacteria suggests that the two known types of phytoene dehydrogenase are more closely related to each other than previously thought.

Iturriaga EA, Velayos A, Eslava AP. 2000. Structure and function of the genes involved in the biosynthesis of carotenoids in the mucorales Biotechnology and Bioprocess Engineering, 5 (4), pp. 263-274. | Show Abstract | Read more

Carotenoids are widely distributed natural pigments which are in an increasing demand by the market, due to their applications in the human food, animal feed, cosmetics, and pharmaceutical industries. Although more than 600 carotenoids have been identified in nature, only a few are industrially important (β-carotene, astaxanthin, lutein or lycopene). To date chemical processes manufacture most of the carotenoid production, but the interest for carotenoids of biological origin is growing since there is an increased public concern over the safety of artificial food colorants. Although much interest and effort has been devoted to the use of biological sources for industrially important carotenoids, only the production of biological β-carotene and astaxanthin has been reported. Among fungi, several Mucorales strains, particularly Blakeslea trispora, have been used to develop fermentation processes for the production of β-carotene on almost competitive cost-price levels. Similarly, the basidiomycetous yeast Xanthophyllomyces dendrorhous (the perfect state of Phaffia rhodozyma), has been proposed as a promising source of astaxanthin. This paper focuses on recent findings on the fungal pathways for carotenoid production, especially the structure and function of the genes involved in the biosynthesis of carotenoids in the Mucorales. An outlook of the possibilities of an increased industrial production of carotenoids, based on metabolic engineering of fungi for carotenoid content and composition, is also discussed.

Velayos A, Alvarez MI, Eslava AP, Iturriaga EA. 1998. Interallelic complementation at the pyrF locus and the homodimeric nature of orotate phosphoribosyltransferase (OPRTase) in Mucor circinelloides. Mol Gen Genet, 260 (2-3), pp. 251-260. | Show Abstract | Read more

Using 5-fluoroorotic acid (5-FOA) as a positive selection system we isolated mutants of Mucor circinelloides altered in the pyrimidine biosynthetic pathway. These mutants were found to be deficient either in orotidine-5'-monophosphate decarboxylase (OMPdecase), or in orotate phosphoribosyltransferase (OPRTase) activity. Complementation tests among mutants lacking OPRTase activity classified them into three groups, thus suggesting the possibility of interallelic complementation. To investigate this hypothesis a cDNA clone corresponding to the OPRTase-encoding gene of M. circinelloides was isolated by direct complementation of E. coli. The genomic copy transformed to prototrophy one member of each of the three classes of OPRTase-deficient mutants. We therefore concluded that they were all altered at the same locus, the pyrF locus. The corresponding alleles were cloned and sequenced. Comparisons of the amino acid sequence of M. circinelloides OPRTase with those of E. coli and S. typhimurium revealed a high degree of similarity in secondary and tertiary structure. As the two bacterial enzymes exist as dimers, a homodimeric quaternary structure of the M. circinelloides mature protein can be assumed. This would also explain the interallelic complementation between some pyrF mutants. The mutations found could affect either the active site or the structure of the dimer interface of the OPRTase.

Velayos A, López-Matas MA, Ruiz-Hidalgo MJ, Eslava AP. 1997. Complementation analysis of carotenogenic mutants of Mucor circinelloides. Fungal Genet Biol, 22 (1), pp. 19-27. | Show Abstract | Read more

Mutants of the filamentous fungus Mucor circinelloides altered in the synthesis of beta-carotene (genotype car) have been isolated by direct inspection of the color shown by the colonies derived from mutagenized spores. The mutants were analyzed for the carotenoid content in darkness and light and studied with respect to complementation in heterokaryons made by spheroplast fusion. The results revealed the existence of at least four complementation groups. The carB mutants are white and accumulate phytoene. The carR mutants are red and accumulate lycopene. The carP mutants are most likely disturbed in the synthesis of phytoene: two of them are white and do not accumulate carotenoids; another carP mutant is yellowish, probably because it is leaky. There are three yellowish mutants which belong to one or more complementation groups different from carB, carR, and carP. Two white mutants obtained in a single mutagenization step failed to complement with the carR and the carP mutants. The wild-type and the carB and carR mutants tested for M. circinelloides showed similar photoinduction.

Ruiz-Hidalgo MJ, López-Matas MA, Velayos A, Fraser PD, Bramley PM, Eslava AP. 1995. Carotenoid Mutants of Mucor circinelloides Botanica Acta, 108 (4), pp. 396-400. | Show Abstract | Read more

The wild‐type of the filamentous fungus Mucor circinelloides accumulates the yellow pigment β‐carotene. At a continuous blue‐light fluence rate of 0.1 W/m 2 the β‐carotene content increases about eight fold over the dark controls. Among the mutants isolated after exposure of spores to either N‐methyl‐N'‐nitro‐N‐nitrosoguanidine or ICR‐170, a red mutant accumulating lycopene, white mutants accumulating phytoene and white mutants without carotenoids were found. The biosynthesis of carotenoids in M. circinelloides shows similarities with that of the fungus Phycomyces blakesleeanus such as the presence of mutants in the same structural genes and the induction by light of the pathway. However, negative end‐product regulation by β‐carotene on the biosynthetic pathway, as in Phycomyces, is absent in M. circinelloides. In contrast to Phycomyces carB and carR mutants, carotenoids in corresponding mutants of M. circinelloides are photoinduced. 1995 Deutsche Botanische Gesellschaft/German Botanical Society

Guidi LG, Mattley J, Martinez-Garay I, Monaco AP, Linden JF, Velayos-Baeza A, Molnár Z. 2017. Knockout Mice for Dyslexia Susceptibility Gene Homologs KIAA0319 and KIAA0319L have Unaffected Neuronal Migration but Display Abnormal Auditory Processing. Cereb Cortex, 27 (12), pp. 5831-5845. | Show Abstract | Read more

Developmental dyslexia is a neurodevelopmental disorder that affects reading ability caused by genetic and non-genetic factors. Amongst the susceptibility genes identified to date, KIAA0319 is a prime candidate. RNA-interference experiments in rats suggested its involvement in cortical migration but we could not confirm these findings in Kiaa0319-mutant mice. Given its homologous gene Kiaa0319L (AU040320) has also been proposed to play a role in neuronal migration, we interrogated whether absence of AU040320 alone or together with KIAA0319 affects migration in the developing brain. Analyses of AU040320 and double Kiaa0319;AU040320 knockouts (dKO) revealed no evidence for impaired cortical lamination, neuronal migration, neurogenesis or other anatomical abnormalities. However, dKO mice displayed an auditory deficit in a behavioral gap-in-noise detection task. In addition, recordings of click-evoked auditory brainstem responses revealed suprathreshold deficits in wave III amplitude in AU040320-KO mice, and more general deficits in dKOs. These findings suggest that absence of AU040320 disrupts firing and/or synchrony of activity in the auditory brainstem, while loss of both proteins might affect both peripheral and central auditory function. Overall, these results stand against the proposed role of KIAA0319 and AU040320 in neuronal migration and outline their relationship with deficits in the auditory system.

Franquinho F, Nogueira-Rodrigues J, Duarte JM, Esteves SS, Carter-Su C, Monaco AP, Molnár Z, Velayos-Baeza A, Brites P, Sousa MM. 2017. The Dyslexia-susceptibility Protein KIAA0319 Inhibits Axon Growth Through Smad2 Signaling. Cereb Cortex, 27 (3), pp. 1732-1747. | Show Abstract | Read more

KIAA0319 is a transmembrane protein associated with dyslexia with a presumed role in neuronal migration. Here we show that KIAA0319 expression is not restricted to the brain but also occurs in sensory and spinal cord neurons, increasing from early postnatal stages to adulthood and being downregulated by injury. This suggested that KIAA0319 participates in functions unrelated to neuronal migration. Supporting this hypothesis, overexpression of KIAA0319 repressed axon growth in hippocampal and dorsal root ganglia neurons; the intracellular domain of KIAA0319 was sufficient to elicit this effect. A similar inhibitory effect was observed in vivo as axon regeneration was impaired after transduction of sensory neurons with KIAA0319. Conversely, the deletion of Kiaa0319 in neurons increased neurite outgrowth in vitro and improved axon regeneration in vivo. At the mechanistic level, KIAA0319 engaged the JAK2-SH2B1 pathway to activate Smad2, which played a central role in KIAA0319-mediated repression of axon growth. In summary, we establish KIAA0319 as a novel player in axon growth and regeneration with the ability to repress the intrinsic growth potential of axons. This study describes a novel regulatory mechanism operating during peripheral nervous system and central nervous system axon growth, and offers novel targets for the development of effective therapies to promote axon regeneration.

Martinez-Garay I, Guidi LG, Holloway ZG, Bailey MAG, Lyngholm D, Schneider T, Donnison T, Butt SJB, Monaco AP, Molnár Z, Velayos-Baeza A. 2017. Normal radial migration and lamination are maintained in dyslexia-susceptibility candidate gene homolog Kiaa0319 knockout mice. Brain Struct Funct, 222 (3), pp. 1367-1384. | Show Abstract | Read more

Developmental dyslexia is a common disorder with a strong genetic component, but the underlying molecular mechanisms are still unknown. Several candidate dyslexia-susceptibility genes, including KIAA0319, DYX1C1, and DCDC2, have been identified in humans. RNA interference experiments targeting these genes in rat embryos have shown impairments in neuronal migration, suggesting that defects in radial cortical migration could be involved in the disease mechanism of dyslexia. Here we present the first characterisation of a Kiaa0319 knockout mouse line. Animals lacking KIAA0319 protein do not show anatomical abnormalities in any of the layered structures of the brain. Neurogenesis and radial migration of cortical projection neurons are not altered, and the intrinsic electrophysiological properties of Kiaa0319-deficient neurons do not differ from those of wild-type neurons. Kiaa0319 overexpression in cortex delays radial migration, but does not affect final neuronal position. However, knockout animals show subtle differences suggesting possible alterations in anxiety-related behaviour and in sensorimotor gating. Our results do not reveal a migration disorder in the mouse model, adding to the body of evidence available for Dcdc2 and Dyx1c1 that, unlike in the rat in utero knockdown models, the dyslexia-susceptibility candidate mouse homolog genes do not play an evident role in neuronal migration. However, KIAA0319 protein expression seems to be restricted to the brain, not only in early developmental stages but also in adult mice, indicative of a role of this protein in brain function. The constitutive and conditional knockout lines reported here will be useful tools for further functional analyses of Kiaa0319.

Mehta ZB, Fine N, Pullen TJ, Cane MC, Hu M, Chabosseau P, Meur G, Velayos-Baeza A, Monaco AP, Marselli L et al. 2016. Changes in the expression of the type 2 diabetes-associated gene VPS13C in the β-cell are associated with glucose intolerance in humans and mice. Am J Physiol Endocrinol Metab, 311 (2), pp. E488-E507. | Show Abstract | Read more

Single nucleotide polymorphisms (SNPs) close to the VPS13C, C2CD4A and C2CD4B genes on chromosome 15q are associated with impaired fasting glucose and increased risk of type 2 diabetes. eQTL analysis revealed an association between possession of risk (C) alleles at a previously implicated causal SNP, rs7163757, and lowered VPS13C and C2CD4A levels in islets from female (n = 40, P < 0.041) but not from male subjects. Explored using promoter-reporter assays in β-cells and other cell lines, the risk variant at rs7163757 lowered enhancer activity. Mice deleted for Vps13c selectively in the β-cell were generated by crossing animals bearing a floxed allele at exon 1 to mice expressing Cre recombinase under Ins1 promoter control (Ins1Cre). Whereas Vps13c(fl/fl):Ins1Cre (βVps13cKO) mice displayed normal weight gain compared with control littermates, deletion of Vps13c had little effect on glucose tolerance. Pancreatic histology revealed no significant change in β-cell mass in KO mice vs. controls, and glucose-stimulated insulin secretion from isolated islets was not altered in vitro between control and βVps13cKO mice. However, a tendency was observed in female null mice for lower insulin levels and β-cell function (HOMA-B) in vivo. Furthermore, glucose-stimulated increases in intracellular free Ca(2+) were significantly increased in islets from female KO mice, suggesting impaired Ca(2+) sensitivity of the secretory machinery. The present data thus provide evidence for a limited role for changes in VPS13C expression in conferring altered disease risk at this locus, particularly in females, and suggest that C2CD4A may also be involved.

Yang R-Y, Xue H, Yu L, Velayos-Baeza A, Monaco AP, Liu F-T. 2016. Identification of VPS13C as a Galectin-12-Binding Protein That Regulates Galectin-12 Protein Stability and Adipogenesis. PLoS One, 11 (4), pp. e0153534. | Show Abstract | Read more

Galectin-12, a member of the galectin family of β-galactoside-binding animal lectins, is preferentially expressed in adipocytes and required for adipocyte differentiation in vitro. This protein was recently found to regulate lipolysis, whole body adiposity, and glucose homeostasis in vivo. Here we identify VPS13C, a member of the VPS13 family of vacuolar protein sorting-associated proteins highly conserved throughout eukaryotic evolution, as a major galectin-12-binding protein. VPS13C is upregulated during adipocyte differentiation, and is required for galectin-12 protein stability. Knockdown of Vps13c markedly reduces the steady-state levels of galectin-12 by promoting its degradation through primarily the lysosomal pathway, and impairs adipocyte differentiation. Our studies also suggest that VPS13C may have a broader role in protein quality control. The regulation of galectin-12 stability by VPS13C could potentially be exploited for therapeutic intervention of obesity and related metabolic diseases.

Holloway ZG, Velayos-Baeza A, Howell GJ, Levecque C, Ponnambalam S, Sztul E, Monaco AP. 2013. Trafficking of the Menkes copper transporter ATP7A is regulated by clathrin-, AP-2-, AP-1-, and Rab22-dependent steps. Mol Biol Cell, 24 (11), pp. 1735-S8. | Show Abstract | Read more

The transporter ATP7A mediates systemic copper absorption and provides cuproenzymes in the trans-Golgi network (TGN) with copper. To regulate metal homeostasis, ATP7A constitutively cycles between the TGN and plasma membrane (PM). ATP7A trafficking to the PM is elevated in response to increased copper load and is reversed when copper concentrations are lowered. Molecular mechanisms underlying this trafficking are poorly understood. We assess the role of clathrin, adaptor complexes, lipid rafts, and Rab22a in an attempt to decipher the regulatory proteins involved in ATP7A cycling. While RNA interference (RNAi)-mediated depletion of caveolin 1/2 or flotillin had no effect on ATP7A localization, clathrin heavy chain depletion or expression of AP180 dominant-negative mutant not only disrupted clathrin-regulated pathways, but also blocked PM-to-TGN internalization of ATP7A. Depletion of the μ subunits of either adaptor protein-2 (AP-2) or AP-1 using RNAi further provides evidence that both clathrin adaptors are important for trafficking of ATP7A from the PM to the TGN. Expression of the GTP-locked Rab22aQ64L mutant caused fragmentation of TGN membrane domains enriched for ATP7A. These appear to be a subdomain of the mammalian TGN, showing only partial overlap with the TGN marker golgin-97. Of importance, ATP7A remained in the Rab22aQ64L-generated structures after copper treatment and washout, suggesting that forward trafficking out of this compartment was blocked. This study provides evidence that multiple membrane-associated factors, including clathrin, AP-2, AP-1, and Rab22, are regulators of ATP7A trafficking.

Velayos-Baeza A, Holinski-Feder E, Neitzel B, Bader B, Critchley EMR, Monaco AP, Danek A, Walker RH. 2011. Chorea-acanthocytosis genotype in the original critchley kentucky neuroacanthocytosis kindred. Arch Neurol, 68 (10), pp. 1330-1333. | Show Abstract | Read more

OBJECTIVE: To determine the molecular nature of the neurological disease in the seminal family reported by Critchley et al in the 1960s, characterized by a hyperkinetic movement disorder and the appearance of acanthocytosis on peripheral blood smear. The eponym Levine-Critchley syndrome, subsequently termed neuroacanthocytosis, has been applied to symptomatically similar, but genetically distinct, disorders, resulting in clinical and diagnostic confusion. DESIGN: DNA analysis. SETTING: Molecular biology research laboratories. PARTICIPANTS: First- and second-degree relatives of the original Critchley et al proband from Kentucky. MAIN OUTCOME MEASURES: Mutations in the VPS13A gene. RESULTS: A mutation was identified in the VPS13A gene, responsible for autosomal recessive chorea-acanthocytosis. Haplotype reconstruction suggested that this mutation was homozygous in the proband. CONCLUSION: These findings strongly support the diagnosis of chorea-acanthocytosis as the disorder described in the original report.

Velayos-Baeza A, Levecque C, Kobayashi K, Holloway ZG, Monaco AP. 2010. The dyslexia-associated KIAA0319 protein undergoes proteolytic processing with {gamma}-secretase-independent intramembrane cleavage. J Biol Chem, 285 (51), pp. 40148-40162. | Show Abstract | Read more

The KIAA0319 gene has been associated with reading disability in several studies. It encodes a plasma membrane protein with a large, highly glycosylated, extracellular domain. This protein is proposed to function in adhesion and attachment and thought to play an important role during neuronal migration in the developing brain. We have previously proposed that endocytosis of this protein could constitute an important mechanism to regulate its function. Here we show that KIAA0319 undergoes ectodomain shedding and intramembrane cleavage. At least five different cleavage events occur, four in the extracellular domain and one within the transmembrane domain. The ectodomain shedding processing cleaves the extracellular domain, generating several small fragments, including the N-terminal region with the Cys-rich MANEC domain. It is possible that these fragments are released to the extracellular medium and trigger cellular responses. The intramembrane cleavage releases the intracellular domain from its membrane attachment. Our results suggest that this cleavage event is not carried out by γ-secretase, the enzyme complex involved in similar processing in many other type I proteins. The soluble cytoplasmic domain of KIAA0319 is able to translocate to the nucleus, accumulating in nucleoli after overexpression. This fragment has an unknown role, although it could be involved in regulation of gene expression. The absence of DNA-interacting motifs indicates that such a function would most probably be mediated through interaction with other proteins, not by direct DNA binding. These results suggest that KIAA0319 not only has a direct role in neuronal migration but may also have additional signaling functions.

Levecque C, Velayos-Baeza A, Holloway ZG, Monaco AP. 2009. The dyslexia-associated protein KIAA0319 interacts with adaptor protein 2 and follows the classical clathrin-mediated endocytosis pathway. Am J Physiol Cell Physiol, 297 (1), pp. C160-C168. | Show Abstract | Read more

Recently, genetic studies have implicated KIAA0319 in developmental dyslexia, the most common of the childhood learning disorders. The first functional data indicated that the KIAA0319 protein is expressed on the plasma membrane and may be involved in neuronal migration. Further analysis of the subcellular distribution of the overexpressed protein in mammalian cells indicates that KIAA0319 can colocalize with the early endosomal marker early endosome antigen 1 (EEA1) in large intracellular vesicles, suggesting that it is endocytosed. Antibody internalization assays with full-length KIAA0319 and deletion constructs confirmed that KIAA0319 is internalized and showed the importance of the cytoplasmic juxtamembranal region in this process. The present study has identified the medium subunit (mu2) of adaptor protein 2 (AP-2) as a binding partner of KIAA0319 in a yeast two-hybrid screen. Using Rab5 mutants or depletion of the mu-subunit of AP-2 or clathrin heavy chain by RNA interference, we demonstrate that KIAA0319 follows a clathrin-mediated endocytic pathway. We also identify tyrosine-995 of KIAA0319 as a critical amino acid required for the interaction with AP-2 and subsequent internalization. These results suggest the surface expression of KIAA0319 is regulated by endocytosis, supporting the idea that the internalization and recycling of the protein may be involved in fine tuning its role in neuronal migration.

Velayos-Baeza A, Toma C, Paracchini S, Monaco AP. 2008. The dyslexia-associated gene KIAA0319 encodes highly N- and O-glycosylated plasma membrane and secreted isoforms. Hum Mol Genet, 17 (6), pp. 859-871. | Show Abstract | Read more

The KIAA0319 gene has been recently associated with developmental dyslexia and shown to be involved in neuronal migration. The deduced KIAA0319 protein contains several polycystic kidney disease (PKD) domains which may mediate the interaction between neurons and glial fibres during neuronal migration. We have previously reported the presence of several alternative splicing variants, some of which are predicted to affect the deduced protein. In this study, we over-expressed constructs containing the main form (A) and two alternative variants (B and C) of KIAA0319. We show that the full-length KIAA0319 (A) is a type I plasma membrane protein, a topology consistent with its proposed function in neuronal migration. The oligomeric status of KIAA0319 is mainly dimeric, and this condition depends on the cysteine-rich regions of the protein, especially the transmembrane (TM) domain and surrounding sequence. KIAA0319 is highly glycosylated in different mammalian cell lines. The central region including the PKD domains is N-glycosylated. Furthermore, a short fragment N-terminal to the PKD domains contains mucin-type O-glycosylation. The two alternative isoforms are soluble proteins lacking the TM domain and, interestingly, only isoform B is secreted. KIAA0319-deletion proteins lacking the TM domain were also secreted. These results suggest that KIAA0319 could be involved not only in cell-cell interactions, but also in signalling.

Francks C, Maegawa S, Laurén J, Abrahams BS, Velayos-Baeza A, Medland SE, Colella S, Groszer M, McAuley EZ, Caffrey TM et al. 2007. LRRTM1 on chromosome 2p12 is a maternally suppressed gene that is associated paternally with handedness and schizophrenia. Mol Psychiatry, 12 (12), pp. 1129-1057. | Show Abstract | Read more

Left-right asymmetrical brain function underlies much of human cognition, behavior and emotion. Abnormalities of cerebral asymmetry are associated with schizophrenia and other neuropsychiatric disorders. The molecular, developmental and evolutionary origins of human brain asymmetry are unknown. We found significant association of a haplotype upstream of the gene LRRTM1 (Leucine-rich repeat transmembrane neuronal 1) with a quantitative measure of human handedness in a set of dyslexic siblings, when the haplotype was inherited paternally (P=0.00002). While we were unable to find this effect in an epidemiological set of twin-based sibships, we did find that the same haplotype is overtransmitted paternally to individuals with schizophrenia/schizoaffective disorder in a study of 1002 affected families (P=0.0014). We then found direct confirmatory evidence that LRRTM1 is an imprinted gene in humans that shows a variable pattern of maternal downregulation. We also showed that LRRTM1 is expressed during the development of specific forebrain structures, and thus could influence neuronal differentiation and connectivity. This is the first potential genetic influence on human handedness to be identified, and the first putative genetic effect on variability in human brain asymmetry. LRRTM1 is a candidate gene for involvement in several common neurodevelopmental disorders, and may have played a role in human cognitive and behavioral evolution.

Velayos-Baeza A, Toma C, da Roza S, Paracchini S, Monaco AP. 2007. Alternative splicing in the dyslexia-associated gene KIAA0319. Mamm Genome, 18 (9), pp. 627-634. | Show Abstract | Read more

The KIAA0319 gene in chromosome 6p22 has been strongly associated with developmental dyslexia. In this article we show a wide expression pattern of this gene in human adult brain by Northern blot analysis. We also performed RT-PCR analysis to detect alternative splicing variants in human brain. Most of the detected variants involve alternative splicing of the exons at the 5' and the 3' ends. Two main forms differing in the length of the 5' UTR are detected at approximately the same rate. Two variants (B and C) lacking exon 19, which encodes the transmembrane domain, are the main alternative forms detected among those predicted to encode protein. These two variants could be secreted and might be involved in signaling functions. A similar RT-PCR analysis performed in mouse and rat adult brains showed that only some of the alternative splicing variants are equivalent to those found in the human gene.

Dobson-Stone C, Velayos-Baeza A, Jansen A, Andermann F, Dubeau F, Robert F, Summers A, Lang AE, Chouinard S, Danek A et al. 2005. Identification of a VPS13A founder mutation in French Canadian families with chorea-acanthocytosis. Neurogenetics, 6 (3), pp. 151-158. | Show Abstract | Read more

Mutations in VPS13A cause chorea-acanthocytosis (ChAc), an autosomal recessive neurodegenerative disorder. VPS13A is located in a tail-to-tail arrangement with GNA14 on chromosome 9q21. ChAc shows substantial allelic heterogeneity, with no single VPS13A mutation causing the majority of cases. We examined 11 patients in four French Canadian ChAc pedigrees for mutations in VPS13A. Affected members of three families were homozygous for a 37-kb deletion of the four terminal exons of VPS13A (EX70_EX73del). This deletion also encompasses the two terminal exons of GNA14. Two affected females in family 4 were homozygous for the splicing mutation 4242+1G>T. Remarkably, the affected males in this highly consanguineous pedigree were compound heterozygotes for EX70_EX73del and 4242+1G>T. PCR analysis of the deletion breakpoint junction revealed that an additional patient with French Canadian ancestry was heterozygous for the EX70_EX73del allele. The identification of a common 9q21 haplotype associated with EX70_EX73del in at least four apparently unrelated ChAc families implies that ChAc shows a founder effect in French Canadians, and that routine testing for EX70_EX73del in suspected ChAc cases may therefore be worthwhile in this population. The deletion breakpoint PCR described here will enable rapid identification of both homozygous and heterozygous carriers of EX70_EX73del.

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