Alternative splicing in the dyslexia-associated gene KIAA0319

KIAA0319 influences cilia length, cell migration and mechanical cell-substrate interaction

Following its association with dyslexia in multiple genetic studies, the KIAA0319 gene has been extensively investigated in different animal models but its function in neurodevelopment remains poorly understood. We developed the first human cellular knockout model for KIAA0319 in RPE1 retinal pigment epithelia cells via CRISPR-Cas9n to investigate its role in processes suggested but not confirmed in previous studies, including cilia formation and cell migration. We observed in the KIAA0319 knockout increased cilia length and accelerated cell migration. Using Elastic Resonator Interference Stress Microscopy (ERISM), we detected an increase in cellular force for the knockout cells that was restored by a rescue experiment. Combining ERISM and immunostaining we show that RPE1 cells exert highly dynamic, piconewton vertical pushing forces through actin-rich protrusions that are surrounded by vinculin-rich pulling sites. This protein arrangement and force pattern has previously been associated to podosomes in other cells. KIAA0319 depletion reduces the fraction of cells forming these actin-rich protrusions. Our results suggest an involvement of KIAA0319 in cilia biology and cell-substrate force regulation.

microRNA-592 blockade inhibits oxidative stress injury in Alzheimer's disease astrocytes via the KIAA0319-mediated Keap1/Nrf2/ARE signaling pathway

MicroRNA-592 (miR-592) has been reported to play a significant role in mediating neuronal activity, but its possible link with Alzheimer's disease (AD) remains unclear. We aimed to explore the mechanism of miR-592 in oxidative stress (OS) injury of astrocytes (ASTs) from AD rat models induced by D-galactose or Aβ_25-35 injection. Bioinformatics website and dual-luciferase reporter gene assay clarified the binding affinity between miR-592 and KIAA0319. KIAA0319 was identified as a target gene of miR-592. The mechanism of miR-592, KIAA0319 and the Keap1/Nrf2/ARE signaling pathway in AD was examined after transducing miR-592 mimic, miR-592 inhibitor and siRNA-KIAA0319 into ASTs to query cell viability, OS injury and reactive oxygen species (ROS). The rat models of AD Exhibited highly expressed miR-592 and poorly expressed KIAA0319. Furthermore, inhibition of miR-592 diminished C-Keap1 expression and enhanced N-Nrf2 and NQO1 expression, thus promoting cell viability and reducing OS injury of ASTs. Taken together, these findings suggested that the downregulation of miR-592 inhibited OS injury of ASTs in rat models of AD by up-regulating KIAA0319 through the activation of the Keap1/Nrf2/ARE signaling pathway.

The dyslexia susceptibility KIAA0319 gene shows a specific expression pattern during zebrafish development supporting a role beyond neuronal migration

Dyslexia is a common neurodevelopmental disorder caused by a significant genetic component. The KIAA0319 gene is one of the most robust dyslexia susceptibility factors but its function remains poorly understood. Initial RNA-interference studies in rats suggested a role in neuronal migration whereas subsequent work with double knock-out mouse models for both Kiaa0319 and its paralogue Kiaa0319-like reported effects in the auditory system but not in neuronal migration. To further understand the role of KIAA0319 during neurodevelopment, we carried out an expression study of its zebrafish orthologue at different embryonic stages. We used different approaches including RNAscope in situ hybridization combined with light-sheet microscopy. The results show particularly high expression during the first few hours of development. Later, expression becomes localized in well-defined structures. In addition to high expression in the brain, we report for the first time expression in the eyes and the notochord. Surprisingly, kiaa0319-like, which generally shows a similar expression pattern to kiaa0319, was not expressed in the notochord suggesting a distinct role for kiaa0319 in this structure. This observation was supported by the identification of notochord enhancers enriched upstream of the KIAA0319 transcription start site, in both zebrafish and humans. This study supports a developmental role for KIAA0319 in the brain as well as in other developing structures, particularly in the notochord which, is key for establishing body patterning in vertebrates.

Knockout Mice for Dyslexia Susceptibility Gene Homologs KIAA0319 and KIAA0319L have Unaffected Neuronal Migration but Display Abnormal Auditory Processing

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.

Normal radial migration and lamination are maintained in dyslexia-susceptibility candidate gene homolog Kiaa0319 knockout mice

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.

The Dyslexia-susceptibility Protein KIAA0319 Inhibits Axon Growth Through Smad2 Signaling

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.

Human cell adhesion molecules: annotated functional subtypes and overrepresentation of addiction-associated genes

Human cell adhesion molecules (CAMs) are essential for proper development, modulation, and maintenance of interactions between cells and cell-to-cell (and matrix-to-cell) communication about these interactions. Despite the differential functional significance of these roles, there have been surprisingly few systematic studies to enumerate the universe of CAMs and identify specific CAMs in distinct functions. In this paper, we update and review the set of human genes likely to encode CAMs with searches of databases, literature reviews, and annotations. We describe likely CAMs and functional subclasses, including CAMs that have a primary function in information exchange (iCAMs), CAMs involved in focal adhesions, CAM gene products that are preferentially involved with stereotyped and morphologically identifiable connections between cells (e.g., adherens junctions, gap junctions), and smaller numbers of CAM genes in other classes. We discuss a novel proposed mechanism involving selective anchoring of the constituents of iCAM-containing lipid rafts in zones of close neuronal apposition to membranes expressing iCAM binding partners. We also discuss data from genetic and genomic studies of addiction in humans and mouse models to highlight the ways in which CAM variation may contribute to a specific brain-based disorder such as addiction. Specific examples include changes in CAM mRNA splicing mediated by differences in the addiction-associated splicing regulator RBFOX1/A2BP1 and CAM expression in dopamine neurons.

Decision tree analysis of genetic risk for clinically heterogeneous Alzheimer's disease

BACKGROUND

Heritability of Alzheimer's disease (AD) is estimated at 74% and genetic contributors have been widely sought. The ε4 allele of apolipoprotein E (APOE) remains the strongest common risk factor for AD, with numerous other common variants contributing only modest risk for disease. Variability in clinical presentation of AD, which is typically amnestic (AmnAD) but can less commonly involve visuospatial, language and/or dysexecutive syndromes (atypical or AtAD), further complicates genetic analyses. Taking a multi-locus approach may increase the ability to identify individuals at highest risk for any AD syndrome. In this study, we sought to develop and investigate the utility of a multi-variant genetic risk assessment on a cohort of phenotypically heterogeneous patients with sporadic AD clinical diagnoses.

METHODS

We genotyped 75 variants in our cohort and, using a two-staged study design, we developed a 17-marker AD risk score in a Discovery cohort (n = 59 cases, n = 133 controls) then assessed its utility in a second Validation cohort (n = 126 cases, n = 150 controls). We also performed a data-driven decision tree analysis to identify genetic and/or demographic criteria that are most useful for accurately differentiating all AD cases from controls.

RESULTS

We confirmed APOE ε4 as a strong risk factor for AD. A 17-marker risk panel predicted AD significantly better than APOE genotype alone (P < 0.00001) in the Discovery cohort, but not in the Validation cohort. In decision tree analyses, we found that APOE best differentiated cases from controls only in AmnAD but not AtAD. In AtAD, HFE SNP rs1799945 was the strongest predictor of disease; variation in HFE has previously been implicated in AD risk in non-ε4 carriers.

CONCLUSIONS

Our study suggests that APOE ε4 remains the best predictor of broad AD risk when compared to multiple other genetic factors with modest effects, that phenotypic heterogeneity in broad AD can complicate simple polygenic risk modeling, and supports the association between HFE and AD risk in individuals without APOE ε4.

Association study of developmental dyslexia candidate genes DCDC2 and KIAA0319 in Chinese population

Developmental dyslexia (DD) is characterized by difficulties in reading and spelling independent of intelligence, educational backgrounds and neurological injuries. Increasing evidences supported DD as a complex genetic disorder and identified four DD candidate genes namely DYX1C1, DCDC2, KIAA0319 and ROBO1. As such, DCDC2 and KIAA0319 are located in DYX2, one of the most studied DD susceptibility loci. However, association of these two genes with DD was inconclusive across different populations. Given the linguistic and genetic differences between Chinese and other populations, it is worthwhile to investigate association of DCDC2 and KIAA0319 with Chinese dyslexic children. Here, we selected 60 tag SNPs covering DCDC2 and KIAA0319 followed by high density genotyping in a large unrelated Chinese cohort with 502 dyslexic cases and 522 healthy controls. Several SNPs (Pmin = 0.0192) of DCDC2 and KIAA0319 as well as a four-maker haplotype (Padjusted = 0.0289, Odds Ratio (OR) = 1.3400) of KIAA0319 showed nominal association with DD. However, none of these results survived Bonferroni correction for multiple comparisons. Thus, the association of DCDC2 and KIAA0319 with DD in Chinese population should be further validated and their contribution to DD etiology and pathology should be interpreted with caution.

Reading and language disorders: the importance of both quantity and quality

Reading and language disorders are common childhood conditions that often co-occur with each other and with other neurodevelopmental impairments. There is strong evidence that disorders, such as dyslexia and Specific Language Impairment (SLI), have a genetic basis, but we expect the contributing genetic factors to be complex in nature. To date, only a few genes have been implicated in these traits. Their functional characterization has provided novel insight into the biology of neurodevelopmental disorders. However, the lack of biological markers and clear diagnostic criteria have prevented the collection of the large sample sizes required for well-powered genome-wide screens. One of the main challenges of the field will be to combine careful clinical assessment with high throughput genetic technologies within multidisciplinary collaborations.

The genetic relationship between handedness and neurodevelopmental disorders

Handedness and brain asymmetry have been linked to neurodevelopmental disorders such as dyslexia and schizophrenia. The genetic nature of this correlation is not understood. Recent discoveries have shown handedness is determined in part by the biological pathways that establish left/right (LR) body asymmetry during development. Cilia play a key role in this process, and candidate genes for dyslexia have also been recently shown to be involved in cilia formation. Defective cilia result not only in LR body asymmetry phenotypes but also brain midline phenotypes such as an absent corpus callosum. These findings suggest that the mechanisms for establishing LR asymmetry in the body are reused for brain midline development, which in turn influences traits such as handedness and reading ability.

Molecular genetics of dyslexia: an overview

Dyslexia is a highly heritable learning disorder with a complex underlying genetic architecture. Over the past decade, researchers have pinpointed a number of candidate genes that may contribute to dyslexia susceptibility. Here, we provide an overview of the state of the art, describing how studies have moved from mapping potential risk loci, through identification of associated gene variants, to characterization of gene function in cellular and animal model systems. Work thus far has highlighted some intriguing mechanistic pathways, such as neuronal migration, axon guidance, and ciliary biology, but it is clear that we still have much to learn about the molecular networks that are involved. We end the review by highlighting the past, present, and future contributions of the Dutch Dyslexia Programme to studies of genetic factors. In particular, we emphasize the importance of relating genetic information to intermediate neurobiological measures, as well as the value of incorporating longitudinal and developmental data into molecular designs.

Position of neocortical neurons transfected at different gestational ages with shRNA targeted against candidate dyslexia susceptibility genes

Developmental dyslexia is a language learning disorder that affects approximately 4–10% of the population. A number of candidate dyslexia susceptibility genes have been identified, including DCDC2 and KIAA0319 on Chromosome (Chr) 6p22.2 and DYX1C1 on Chr 15q21. Embryonic knockdown of the function of homologs of these genes in rat neocortical projection cell progenitors by in utero electroporation of plasmids encoding small hairpin RNA (shRNA) revealed that all three genes disrupted neuronal migration to the neocortex. Specifically, this disruption would result in heterotopia formation (Dyx1c1 and Kiaa0319) and/or overmigration past their expected laminar location (Dyx1c1 and Dcdc2). In these experiments, neurons normally destined for the upper neocortical laminæ were transfected on embryonic day (E) 15.5, and we designed experiments to test whether these migration phenotypes were the result of targeting a specific type of projection neuron. We transfected litters with Dcdc2 shRNA, Dyx1c1 shRNA, Kiaa0319 shRNA, or fluorescent protein (as a control) at each of three gestational ages (E14.5, E15.5, or E16.5). Pups were allowed to come to term, and their brains were examined at 3 weeks of age for the position of transfected cells. We found that age of transfection did not affect the percentage of unmigrated neurons—transfection with Kiaa0319 shRNA resulted in heterotopia formation at all three ages. Overmigration of neurons transfected with Dcdc2 shRNA, while present following transfections at the later ages, did not occur following E14.5 transfections. These results are considered in light of the known functions of each of these candidate dyslexia susceptibility genes.

The effects of Kiaa0319 knockdown on cortical and subcortical anatomy in male rats

Developmental dyslexia is a disorder characterized by a specific deficit in reading despite adequate overall intelligence and educational resources. The neurological substrate underlying these significant behavioral impairments is not known. Studies of post mortem brain tissue from male and female dyslexic individuals revealed focal disruptions of neuronal migration concentrated in the left hemisphere, along with aberrant symmetry of the right and left the planum temporale, and changes in cell size distribution within the medial geniculate nucleus of the thalamus (Galaburda et al., 1985; Humphreys et al., 1990). More recent neuroimaging studies have identified several changes in the brains of dyslexic individuals, including regional changes in gray matter, changes in white matter, and changes in patterns of functional activation. In a further effort to elucidate the etiology of dyslexia, epidemiological and genetic studies have identified several candidate dyslexia susceptibility genes. Some recent work has investigated associations between some of these genetic variants and structural changes in the brain. Variants of one candidate dyslexia susceptibility gene, KIAA0319, have been linked to morphological changes in the cerebellum and functional activational changes in the superior temporal sulcus (Jamadar et al., 2011; Pinel et al., 2012). Animal models have been used to create a knockdown of Kiaa0319 (the rodent homolog of the human gene) via in utero RNA interference in order to study the gene's effects on brain development and behavior. Studies using this animal model have demonstrated that knocking down the gene leads to focal disruptions of neuronal migration in the form of ectopias and heterotopias, similar to those observed in the brains of human dyslexics. However, further changes to the structure of the brain have not been studied following this genetic disruption. The current study sought to determine the effects of embryonic Kiaa0319 knockdown on volume of the cortex and hippocampus, as well as midsagittal area of the corpus callosum in male rats. Results demonstrate that Kiaa0319 knockdown did not change the volume of the cortex or hippocampus, but did result in a significant reduction in the midsagittal area of the corpus callosum. Taken in the context of previous reports of behavioral deficits following Kiaa0319 knockdown (Szalkowski et al., 2012), and reports that reductions of corpus callosum size are related to processing deficits in humans (Paul, 2011), these results suggest that Kiaa0319 has a specific involvement in neural systems important for temporal processing.

The genetics of reading disabilities: from phenotypes to candidate genes

This article provides an overview of (a) issues in definition and diagnosis of specific reading disabilities at the behavioral level that may occur in different constellations of developmental and phenotypic profiles (patterns); (b) rapidly expanding research on genetic heterogeneity and gene candidates for dyslexia and other reading disabilities; (c) emerging research on gene-brain relationships; and (d) current understanding of epigenetic mechanisms whereby environmental events may alter behavioral expression of genetic variations. A glossary of genetic terms (denoted by bold font) is provided for readers not familiar with the technical terms.

Neocortical disruption and behavioral impairments in rats following in utero RNAi of candidate dyslexia risk gene Kiaa0319

Within the last decade several genes have been identified as candidate risk genes for developmental dyslexia. Recent research using animal models and embryonic RNA interference (RNAi) has shown that a subset of the candidate dyslexia risk genes--DYX1C1, ROBO1, DCDC2, KIAA0319--regulate critical parameters of neocortical development, such as neuronal migration. For example, embryonic disruption of the rodent homolog of DYX1C1 disrupts neuronal migration and produces deficits in rapid auditory processing (RAP) and working memory--phenotypes that have been reported to be associated with developmental dyslexia. In the current study we used a modified prepulse inhibition paradigm to assess acoustic discrimination abilities of male Wistar rats following in utero RNA interference targeting Kiaa0319. We also assessed spatial learning and working memory using a Morris water maze (MWM) and a radial arm water maze. We found that embryonic interference with this gene resulted in disrupted migration of neocortical neurons leading to formation of heterotopia in white matter, and to formation of hippocampal dysplasia in a subset of animals. These animals displayed deficits in processing complex acoustic stimuli, and those with hippocampal malformations exhibited impaired spatial learning abilities. No significant impairment in working memory was detected in the Kiaa0319 RNAi treated animals. Taken together, these results suggest that Kiaa0319 plays a role in neuronal migration during embryonic development, and that early interference with this gene results in an array of behavioral deficits including impairments in rapid auditory processing and simple spatial learning.

A theoretical molecular network for dyslexia: integrating available genetic findings

Developmental dyslexia is a common specific childhood learning disorder with a strong heritable component. Previous studies using different genetic approaches have identified several genetic loci and candidate genes for dyslexia. In this article, we have integrated the current knowledge on 14 dyslexia candidate genes suggested by cytogenetic findings, linkage and association studies. We found that 10 of the 14 dyslexia candidate genes (ROBO1, KIAA0319, KIAA0319L, S100B, DOCK4, FMR1, DIP2A, GTF2I, DYX1C1 and DCDC2) fit into a theoretical molecular network involved in neuronal migration and neurite outgrowth. Based on this, we also propose three novel dyslexia candidate genes (SLIT2, HMGB1 and VAPA) from known linkage regions, and we discuss the possible involvement of genes emerging from the two reported genome-wide association studies for reading impairment-related phenotypes in the identified network.

The effects of embryonic knockdown of the candidate dyslexia susceptibility gene homologue Dyx1c1 on the distribution of GABAergic neurons in the cerebral cortex

Developmental dyslexia is a language-based learning disability, and a number of candidate dyslexia susceptibility genes have been identified, including DYX1C1, KIAA0319, and DCDC2. Knockdown of function by embryonic transfection of small hairpin RNA (shRNA) of rat homologues of these genes dramatically disrupts neuronal migration to the cerebral cortex by both cell autonomous and non-cell autonomous effects. Here we sought to investigate the extent of non-cell autonomous effects following in utero disruption of the candidate dyslexia susceptibility gene homolog Dyx1c1 by assessing the effects of this disruption on GABAergic neurons. We transfected the ventricular zone of embryonic day (E) 15.5 rat pups with either Dyx1c1 shRNA, DYX1C1 expression construct, both Dyx1c1 shRNA and DYX1C1 expression construct, or a scrambled version of Dyx1c1 shRNA, and sacrificed them at postnatal day 21. The mothers of these rats were injected with BrdU at either E13.5, E15.5, or E17.5. Neurons transfected with Dyx1c1 shRNA were bi-modally distributed in the cerebral cortex with one population in heterotopic locations at the white matter border and another migrating beyond their expected location in the cerebral cortex. In contrast, there was no disruption of migration following transfection with the DYX1C1 expression construct. We found untransfected GABAergic neurons (parvalbumin, calretinin, and neuropeptide Y) in the heterotopic collections of neurons in Dyx1c1 shRNA treated animals, supporting the hypothesis of non-cell autonomous effects. In contrast, we found no evidence that the position of the GABAergic neurons that made it to the cerebral cortex was disrupted by the embryonic transfection with any of the constructs. Taken together, these results support the notion that neurons within heterotopias caused by transfection with Dyx1c1 shRNA result from both cell autonomous and non-cell autonomous effects, but there is no evidence to support non-cell autonomous disruption of neuronal position in the cerebral cortex itself.

The dyslexia-associated KIAA0319 protein undergoes proteolytic processing with {gamma}-secretase-independent intramembrane cleavage

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.

Progress towards a cellular neurobiology of reading disability

Reading Disability (RD) is a significant impairment in reading accuracy, speed and/or comprehension despite adequate intelligence and educational opportunity. RD affects 5-12% of readers, has a well-established genetic risk, and is of unknown neurobiological cause or causes. In this review we discuss recent findings that revealed neuroanatomic anomalies in RD, studies that identified 3 candidate genes (KIAA0319, DYX1C1, and DCDC2), and compelling evidence that potentially link the function of candidate genes to the neuroanatomic anomalies. A hypothesis has emerged in which impaired neuronal migration is a cellular neurobiological antecedent to RD. We critically evaluate the evidence for this hypothesis, highlight missing evidence, and outline future research efforts that will be required to develop a more complete cellular neurobiology of RD.

The dyslexia-associated protein KIAA0319 interacts with adaptor protein 2 and follows the classical clathrin-mediated endocytosis pathway

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 (μ2) 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 μ-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.

The genetics of reading disability

Genetic factors contribute substantially to the development of reading disability (RD). Family linkage studies have implicated many chromosomal regions containing RD susceptibility genes, of which putative loci at 1p34-p36 (DYX8), 2p (DYX3), 6p21.3 (DYX2), and 15q21 (DYX1) have been frequently replicated, whereas those at 3p12-q12 (DYX5), 6q13-q16 (DYX4), 11p15 (DYX7), 18p11 (DYX6), and Xq27 (DYX9) have less evidence. Association studies of positional candidate genes have implicated DCDC2 and KIAA0319 in DYX2, as well as C2ORF3 and MRPL19 (DYX3), whereas DYX1C1/EKN1 (DYX1) and ROBO1 (DYX5) were found to be disrupted by rare translocation breakpoints in reading-disabled individuals. Four of the candidate genes (DYX1C1, KIAA0319, DCDC2, and ROBO1) appear to function in neuronal migration and guidance, suggesting the importance of early neurodevelopmental processes in RD. Future studies to help us understand the function of these and other RD candidate genes promise to yield enormous insight into the neurobiologic mechanisms underlying the pathophysiology of this disorder.

OKCAM: an ontology-based, human-centered knowledgebase for cell adhesion molecules

‘Cell adhesion molecules’ (CAMs) are essential elements of cell/cell communication that are important for proper development and plasticity of a variety of organs and tissues. In the brain, appropriate assembly and tuning of neuronal connections is likely to require appropriate function of many cell adhesion processes. Genetic studies have linked and/or associated CAM variants with psychiatric, neurologic, neoplastic, immunologic and developmental phenotypes. However, despite increasing recognition of their functional and pathological significance, no systematic study has enumerated CAMs or documented their global features. We now report compilation of 496 human CAM genes in six gene families based on manual curation of protein domain structures, Gene Ontology annotations, and 1487 NCBI Entrez annotations. We map these genes onto a cell adhesion molecule ontology that contains 850 terms, up to seven levels of depth and provides a hierarchical description of these molecules and their functions. We develop OKCAM, a CAM knowledgebase that provides ready access to these data and ontologic system at http://okcam.cbi.pku.edu.cn. We identify global CAM properties that include: (i) functional enrichment, (ii) over-represented regulation modes and expression patterns and (iii) relationships to human Mendelian and complex diseases, and discuss the strengths and limitations of these data.