Orthologous Mouse Gene Research Articles

Bestrophin 1 is indispensable for volume regulation in human retinal pigment epithelium cells

In response to cell swelling, volume-regulated anion channels (VRACs) participate in a process known as regulatory volume decrease (RVD). Only recently, first insight into the molecular identity of mammalian VRACs was obtained by the discovery of the leucine-rich repeats containing 8A (LRRC8A) gene. Here, we show that bestrophin 1 (BEST1) but not LRRC8A is crucial for volume regulation in human retinal pigment epithelium (RPE) cells. Whole-cell patch-clamp recordings in RPE derived from human-induced pluripotent stem cells (hiPSC) exhibit an outwardly rectifying chloride current with characteristic functional properties of VRACs. This current is severely reduced in hiPSC-RPE cells derived from macular dystrophy patients with pathologic BEST1 mutations. Disruption of the orthologous mouse gene (Best1(-/-)) does not result in obvious retinal pathology but leads to a severe subfertility phenotype in agreement with minor endogenous expression of Best1 in murine RPE but highly abundant expression in mouse testis. Sperm from Best1(-/-) mice showed reduced motility and abnormal sperm morphology, indicating an inability in RVD. Together, our data suggest that the molecular identity of VRACs is more complex--that is, instead of a single ubiquitous channel, VRACs could be formed by cell type- or tissue-specific subunit composition. Our findings provide the basis to further examine VRAC diversity in normal and diseased cell physiology, which is key to exploring novel therapeutic approaches in VRAC-associated pathologies.

Abstract A05: The Mouse Tumor Biology (MTB) Database: An electronic tool for identifying and evaluating mouse and PDX models of human cancer

Abstract The increasing number and diversity of available mouse models of human cancer and their growing importance in scientific research have resulted in an enormous increase in the amount and types of data generated from these models. These models represent powerful tools for studying biological and genetic mechanisms of cancer and for translation into potential clinical therapeutics. However, the amount of available data makes it challenging to identify and evaluate specific models and data important for an individual laboratory's research. Placing these data in their proper genetic context is crucial to understanding the biochemical and molecular mechanisms of initiation, progression, and metastasis of different cancers. In addition, the ability of the immunodeficient NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mouse strain to host patient derived xenograft (PDX) models only increases the number of available models and the data produced from them. The Mouse Tumor Biology (MTB) Database provides access to data from mouse and PDX models of human tumors and the tools to analyze these data, facilitating the discovery and evaluation of novel mouse and PDX models of human cancers (http://tumor.informatics.jax.org). MTB includes data on endogenously arising tumors (both spontaneous and induced) in genetically defined mice (inbred, hybrid, mutant, and genetically engineered mice) and information from PDX models of human tumors and provides freely available web access to these data. MTB integrates data from peer-reviewed literature, laboratories studying mouse models of human cancer, production mouse colonies at The Jackson Laboratory (JAX), colonies of aging mice from the Jackson Aging Center, and PDX data from the Jackson Laboratory Patient-derived xenograft resource. MTB also incorporates data from PathBase, and mouse gene expression data sets from NCBI's Gene Expression Omnibus (GEO) and the Array Express Database. Data include tumor classification, incidence and latency, tumor associated quantitative trait loci (QTL), pathology reports, images and genetic changes in tumors (somatic) and background strain (germline). Data type specific query forms (tumor, genetic etc.) allow detailed searches. MTB also can be searched using human gene symbols for orthologous mouse genes and associated data. Pathology images are submitted by the scientific community, from primary literature (with publisher permission), and from JAX colonies. MTB also includes immunohistochemistry data on over 500 antibodies with accompanying images of positive control samples and links to the respective vendors. MTB encourages direct submission of mouse tumor data and images from the cancer research community and has developed a web-based system to facilitate submission of data. Standard nomenclature, controlled vocabularies and literature citations facilitate data integration and robust searches. MTB is integrated with the Mouse Genome Informatics resource (MGI, http://www.informatics.jax.org) and provides links to other related online resources such as the Mouse Phenome Database (MPD), the Biology of the Mammary Gland Web Site, and the NCI Mouse Repository. MTB is supported by NCI grant CA089713. Citation Format: Dale A. Begley, Debra M. Krupke, Steven B. Neuhauser, Joel E. Richardson, John P. Sundberg, Carol J. Bult, Janan T. Eppig. The Mouse Tumor Biology (MTB) Database: An electronic tool for identifying and evaluating mouse and PDX models of human cancer. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr A05.

Core promoter short tandem repeats as evolutionary switch codes for primate speciation.

Alteration in gene expression levels underlies many of the phenotypic differences across species. Because of their highly mutable nature, proximity to the +1 transcription start site (TSS), and the emerging evidence of functional impact on gene expression, core promoter short tandem repeats (STRs) may be considered an ideal source of variation across species. In a genome-scale analysis of the entire Homo sapiens protein-coding genes, we have previously identified core promoters with at least one STR of ≥ 6-repeats, with possible selective advantage in this species. In the current study, we performed reverse analysis of the entire Homo sapiens orthologous genes in mouse in the Ensembl database, in order to identify conserved STRs that have shrunk as an evolutionary advantage to humans. Two protocols were used to minimize ascertainment bias. Firstly, two species sharing a more recent ancestor with Homo sapiens (i.e. Pan troglodytes and Gorilla gorilla gorilla) were also included in the study. Secondly, four non-primate species encompassing the major orders across Mammals, including Scandentia, Laurasiatheria, Afrotheria, and Xenarthra were analyzed as out-groups. We introduce STR evolutionary events specifically identical in primates (i.e. Homo sapiens, Pan troglodytes, and Gorilla gorilla gorilla) vs. non-primate out-groups. The average frequency of the identically shared STR motifs across those primates ranged between 0.00005 and 0.06. The identified genes are involved in important evolutionary and developmental processes, such as normal craniofacial development (TFAP2B), regulation of cell shape (PALMD), learning and long-term memory (RGS14), nervous system development (GFRA2), embryonic limb morphogenesis (PBX2), and forebrain development (APAF1). We provide evidence of core promoter STRs as evolutionary switch codes for primate speciation, and the first instance of identity-by-descent for those motifs at the interspecies level.

Progressive hearing loss and vestibular dysfunction caused by a homozygous nonsense mutation in CLIC5.

In a consanguineous Turkish family diagnosed with autosomal recessive nonsyndromic hearing impairment (arNSHI), a homozygous region of 47.4 Mb was shared by the two affected siblings on chromosome 6p21.1-q15. This region contains 247 genes including the known deafness gene MYO6. No pathogenic variants were found in MYO6, neither with sequence analysis of the coding region and splice sites nor with mRNA analysis. Subsequent candidate gene evaluation revealed CLIC5 as an excellent candidate gene. The orthologous mouse gene is mutated in the jitterbug mutant that exhibits progressive hearing impairment and vestibular dysfunction. Mutation analysis of CLIC5 revealed a homozygous nonsense mutation c.96T>A (p.(Cys32Ter)) that segregated with the hearing loss. Further analysis of CLIC5 in 213 arNSHI patients from mostly Dutch and Spanish origin did not reveal any additional pathogenic variants. CLIC5 mutations are thus not a common cause of arNSHI in these populations. The hearing loss in the present family had an onset in early childhood and progressed from mild to severe or even profound before the second decade. Impaired hearing is accompanied by vestibular areflexia and in one of the patients with mild renal dysfunction. Although we demonstrate that CLIC5 is expressed in many other human tissues, no additional symptoms were observed in these patients. In conclusion, our results show that CLIC5 is a novel arNSHI gene involved in progressive hearing impairment, vestibular and possibly mild renal dysfunction in a family of Turkish origin.

The human δ2 glutamate receptor gene is not mutated in patients with spinocerebellar ataxia.

The human glutamate receptor delta 2 gene (GRID2) shares 90% homology with the orthologous mouse gene. The mouse Grid2 gene is involved with functions of the cerebellum and spontaneous mutation of Grid2 leads to a spinocerebellar ataxia-like phenotype. To investigate whether such mutations occur in humans, we screened for mutations in the coding sequence of GRID2 in 24 patients with familial or sporadic spinocerebellar ataxia and in 52 normal controls. We detected no point mutations or insertion/deletion mutations in the 16 exons of GRID2. However, a polymorphic 4 nucleotide deletion (IVS5-121_-118 GAGT) and two single nucleotide polymorphisms (c.1251G>T and IVS14-63C>G) were identified. The frequency of these polymorphisms was similar between spinocerebellar ataxia patients and normal controls. These data indicate that spontaneous mutations do not occur in GRID2 and that the incidence of spinocerebellar ataxia in humans is not associated with GRID2 mutation or polymorphisms.

Conservation/Mutation in the Splice Sites of Cytokine Receptor Genes of Mouse and Human

Conservation/mutation in the intronic initial and terminal hexanucleotides was studied in 26 orthologous cytokine receptor genes of Mouse and Human. Introns began and ended with the canonical dinucleotides GT and AG, respectively. Identical configurations were found in 57% of the 5′ hexanucleotides and 28% of the 3′ hexanucleotides. The actual conservation percentages of the individual variable nucleotides at each position in the hexanucleotides were determined, and the theoretical rates of conservation of groups of three nucleotides were calculated under the hypothesis of a mutual evolutionary independence of the neighboring nucleotides (random association). Analysis of the actual conservation of groups of variable nucleotides showed that, at 5′, GTGAGx was significantly more expressed and GTAAGx was significantly less expressed, as compared to the random association. At 3′, TTTxAG and xTGCAG were overexpressed as compared to a random association. Study of Mouse and Human transcript variants involving the splice sites showed that most variants were not inherited from the common ancestor but emerged during the process of speciation. In some variants the silencing of a terminal hexanucleotide determined skipping of the downstream exon; in other variants the constitutive splicing hexanucleotide was replaced by another potential, in-frame, splicing hexanucleotide, leading to alterations of exon lengths.

Localisation of the SMC loading complex Nipbl/Mau2 during mammalian meiotic prophase I

Evidence from lower eukaryotes suggests that the chromosomal associations of all the structural maintenance of chromosome (SMC) complexes, cohesin, condensin and Smc5/6, are influenced by the Nipbl/Mau2 heterodimer. Whether this function is conserved in mammals is currently not known. During mammalian meiosis, very different localisation patterns have been reported for the SMC complexes, and the localisation of Nipbl/Mau2 has just recently started to be investigated. Here, we show that Nipbl/Mau2 binds on chromosomal axes from zygotene to mid-pachytene in germ cells of both sexes. In spermatocytes, Nipbl/Mau2 then relocalises to chromocenters, whereas in oocytes it remains bound to chromosomal axes throughout prophase to dictyate arrest. The localisation pattern of Nipbl/Mau2, together with those seen for cohesin, condensin and Smc5/6 subunits, is consistent with a role as a loading factor for cohesin and condensin I, but not for Smc5/6. We also demonstrate that Nipbl/Mau2 localises next to Rad51 and γH2AX foci. NIPBL gene deficiencies are associated with the Cornelia de Lange syndrome in humans, and we find that haploinsufficiency of the orthologous mouse gene results in an altered distribution of double-strand breaks marked by γH2AX during prophase I. However, this is insufficient to result in major meiotic malfunctions, and the chromosomal associations of the synaptonemal complex proteins and the three SMC complexes appear cytologically indistinguishable in wild-type and Nipbl +/− spermatocytes.Electronic supplementary materialThe online version of this article (doi:10.1007/s00412-013-0444-7) contains supplementary material, which is available to authorized users.

Regulation of the F11, Klkb1, Cyp4v3 Gene Cluster in Livers of Metabolically Challenged Mice

Single nucleotide polymorphisms (SNPs) in a 4q35.2 locus that harbors the coagulation factor XI (F11), prekallikrein (KLKB1), and a cytochrome P450 family member (CYP4V2) genes are associated with deep venous thrombosis (DVT). These SNPs exert their effect on DVT by modifying the circulating levels of FXI. However, SNPs associated with DVT were not necessarily all in F11, but also in KLKB1 and CYP4V2. Here, we searched for evidence for common regulatory elements within the 4q35.2 locus, outside the F11 gene, that might control FXI plasma levels and/or DVT risk. To this end, we investigated the regulation of the orthologous mouse gene cluster under several metabolic conditions that impact mouse hepatic F11 transcription. In livers of mice in which HNF4α, a key transcription factor controlling F11, was ablated, or reduced by siRNA, a strong decrease in hepatic F11 transcript levels was observed that correlated with Cyp4v3 (mouse orthologue of CYP4V2), but not by Klkb1 levels. Estrogens induced hepatic F11 and Cyp4v3, but not Klkb1 transcript levels, whereas thyroid hormone strongly induced hepatic F11 transcript levels, and reduced Cyp4v3, leaving Klkb1 levels unaffected. Mice fed a high-fat diet also had elevated F11 transcription, markedly paralleled by an induction of Klkb1 and Cyp4v3 expression. We conclude that within the mouse F11, Klkb1, Cyp4v3 gene cluster, F11 and Cyp4v3 frequently display striking parallel transcriptional responses suggesting the presence of shared regulatory elements.

Comparative Analysis of Temporal and Dose-Dependent TCDD-Elicited Gene Expression in Human, Mouse, and Rat Primary Hepatocytes

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-elicited time- and dose-dependent differential gene expression was compared in human, mouse, and rat primary hepatocytes. Comprehensive time course (10 nM TCDD or dimethyl sulfoxide vehicle control for 1, 2, 4, 8, 12, 24, and 48h) studies identified 495, 2305, and 711 differentially expressed orthologous genes in human, mouse, and rat hepatocytes, respectively. However, only 16 orthologs were differentially expressed across all three species, with the majority of orthologs exhibiting species-specific expression (399 human, 2097 mouse, and 533 rat), consistent with species-specific expression reported in other in vitro and in vivo comparative studies. TCDD also elicited the dose-dependent induction of 397 human, 100 mouse, and 443 rat genes at 12h and 615 human, 426 mouse, and 314 rat genes at 24h. Comparable EC50 values were obtained for AhR battery genes including Cyp1a1 (0.1 nM human, 0.05 nM mouse, 0.08 nM rat at 24h) and Tiparp (0.97 nM human, 0.63 nM mouse, 0.14 nM rat at 12h). Overrepresented functions and pathways included amino acid metabolism in humans, immune response in mice, and energy homeostasis in rats. Differentially expressed genes functionally associated with lipid transport, processing, and metabolism were overrepresented in all three species but exhibited species-specific expression consistent with the induction of hepatic steatosis in mice but not in rats following a single oral gavage of TCDD. Furthermore, human primary hepatocytes showed lipid accumulation following 48h of treatment with TCDD, suggesting that AhR-mediated steatosis in mice more closely resembles human hepatic fat accumulation compared with that in rats. Collectively, these results suggest that species-specific gene expression profiles mediate the species-specific effects of TCDD despite the conservation of the AhR and its signaling mechanism.

GKaKs: the pipeline for genome-level Ka/Ks calculation

gKaKs is a codon-based genome-level Ka/Ks computation pipeline developed and based on programs from four widely used packages: BLAT, BLASTALL (including bl2seq, formatdb and fastacmd), PAML (including codeml and yn00) and KaKs_Calculator (including 10 substitution rate estimation methods). gKaKs can automatically detect and eliminate frameshift mutations and premature stop codons to compute the substitution rates (Ka, Ks and Ka/Ks) between a well-annotated genome and a non-annotated genome or even a poorly assembled scaffold dataset. It is especially useful for newly sequenced genomes that have not been well annotated. We applied gKaKs to estimate the genome-wide substitution rates in five pairs of closely related species. The average Ka and Ks computed by gKaKs were consistent with previous studies. We also compared the Ka, Ks and Ka/Ks of mouse and rat orthologous protein-coding genes estimated by gKaKs and based on the alignments generated by PAL2NAL. Results from two methods are compatible. gKaKs is implemented in Perl and is freely available on http://longlab.uchicago.edu/?q=gKaKs. The detailed user manual is available on the website.

Phenotype-Genotype Correlations in Mouse Models of Amelogenesis Imperfecta Caused by Amelx and Enam Mutations

Mutations in human and in mouse orthologous genes Amelx and Enam result in a diverse range of enamel defects. In this study we aimed to investigate the phenotype-genotype correlation between the mutants and the wild-type controls in mouse models of amelogenesis imperfecta using novel measurement approaches. Ten hemi-mandibles and incisors were dissected from each group of Amelx^WT, Amelx^X/Y64H, Amelx^Y/Y64H, Amelx^Y64H/Y64H, and Enam^WT, Enam^Rgsc395 heterozygous and Enam^Rgsc395 homozygous mice. Their macro-morphology, colour and micro-topography were assessed using bespoke 2D and 3D image analysis systems and customized colour and whiteness algorithms. The novel methods identified significant differences (p ≤ 0.05) between the Amelx groups for mandible and incisor size and enamel colour and between the Enam groups for incisor size and enamel colour. The Amelx^WT mice had the largest mandibles and incisors, followed in descending order of size by the Amelx^X/Y64H, Amelx^Y/Y64H and Amelx^Y64H/Y64H mice. Within the Enam groups the Enam^WT incisors were largest and the Enam^Rgsc395 heterozygous mice were smallest. The effect on tooth morphology was also reflected by the severity of the enamel defects in the colour and whiteness assessment. Amelogenin affected mandible morphology and incisor enamel formation, while enamelin only affected incisors, supporting the multifunctional role of amelogenin. The enamelin mutation was associated with earlier forming enamel defects. The study supported the critical involvement of amelogenin and enamelin in enamel mineralization.

Large-scale objective association of mouse phenotypes with human symptoms through structural variation identified in patients with developmental disorders

Copy number variants (CNVs) are thought to underlie many human developmental abnormalities. However, it is unclear how many of these CNVs exert their pathogenic effects or, in particular, how distinct CNVs at dispersed loci can give rise to the same abnormality. We hypothesize that the mouse orthologs of genes whose copy number change gives rise to the same human abnormality might also yield a similar phenotype when disrupted in mice. Thus, by bringing together a large number of disparate CNVs, we may be able to identify an unusually overrepresented phenotype among the affected genes' mouse orthologs. We obtained 1,624 de novo CNVs identified in patients with developmental abnormalities from Database of Chromosomal Imbalance and Phenotype in Humans Using Ensembl Resources and European Cytogeneticists Association Register of Unbalanced Chromosome Aberrations database. Forming CNV sets for each of 1,088 distinct human abnormalities, we were able to associate a total of 143 (13%) human abnormalities with mouse model phenotypes. Although many mouse phenotypes are readily comparable to their associated human abnormality, others are less so, generating novel biological hypotheses. Of the 2,086 candidate genes that contribute to these associations, 65% have not been previously associated with human disease in Online Mendelian Inheritance in Man, and their distribution suggests both extensive pleiotropy and epistasis while also proposing a small number of simple additive consequences.

A New Look at Vitamin D Metabolism and “Idiopathic” Hypercalcemia

A New Look at Vitamin D Metabolism and “Idiopathic” Hypercalcemia

Mutations in KAT6B, Encoding a Histone Acetyltransferase, Cause Genitopatellar Syndrome

Genitopatellar syndrome (GPS) is a skeletal dysplasia with cerebral and genital anomalies for which the molecular basis has not yet been determined. By exome sequencing, we found de novo heterozygous truncating mutations in KAT6B (lysine acetyltransferase 6B, formerly known as MYST4 and MORF) in three subjects; then by Sanger sequencing of KAT6B, we found similar mutations in three additional subjects. The mutant transcripts do not undergo nonsense-mediated decay in cells from subjects with GPS. In addition, human pathological analyses and mouse expression studies point to systemic roles of KAT6B in controlling organismal growth and development. Myst4 (the mouse orthologous gene) is expressed in mouse tissues corresponding to those affected by GPS. Phenotypic differences and similarities between GPS, the Say-Barber-Biesecker variant of Ohdo syndrome (caused by different mutations of KAT6B), and Rubinstein-Taybi syndrome (caused by mutations in other histone acetyltransferases) are discussed. Together, the data support an epigenetic dysregulation of the limb, brain, and genital developmental programs.

When orthologs diverge between human and mouse

Despite the common assumption that orthologs usually share the same function, there have been various reports of divergence between orthologs, even among species as close as mammals. The comparison of mouse and human is of special interest, because mouse is often used as a model organism to understand human biology. We review the literature on evidence for divergence between human and mouse orthologous genes, and discuss it in the context of biomedical research.

The Orphan Disease Networks

The low prevalence rate of orphan diseases (OD) requires special combined efforts to improve diagnosis, prevention, and discovery of novel therapeutic strategies. To identify and investigate relationships based on shared genes or shared functional features, we have conducted a bioinformatic-based global analysis of all orphan diseases with known disease-causing mutant genes. Starting with a bipartite network of known OD and OD-causing mutant genes and using the human protein interactome, we first construct and topologically analyze three networks: the orphan disease network, the orphan disease-causing mutant gene network, and the orphan disease-causing mutant gene interactome. Our results demonstrate that in contrast to the common disease-causing mutant genes that are predominantly nonessential, a majority of orphan disease-causing mutant genes are essential. In confirmation of this finding, we found that OD-causing mutant genes are topologically important in the protein interactome and are ubiquitously expressed. Additionally, functional enrichment analysis of those genes in which mutations cause ODs shows that a majority result in premature death or are lethal in the orthologous mouse gene knockout models. To address the limitations of traditional gene-based disease networks, we also construct and analyze OD networks on the basis of shared enriched features (biological processes, cellular components, pathways, phenotypes, and literature citations). Analyzing these functionally-linked OD networks, we identified several additional OD-OD relations that are both phenotypically similar and phenotypically diverse. Surprisingly, we observed that the wiring of the gene-based and other feature-based OD networks are largely different; this suggests that the relationship between ODs cannot be fully captured by the gene-based network alone.

Assessment of orthologous splicing isoforms in human and mouse orthologous genes

BackgroundRecent discoveries have highlighted the fact that alternative splicing and alternative transcripts are the rule, rather than the exception, in metazoan genes. Since multiple transcript and protein variants expressed by the same gene are, by definition, structurally distinct and need not to be functionally equivalent, the concept of gene orthology should be extended to the transcript level in order to describe evolutionary relationships between structurally similar transcript variants. In other words, the identification of true orthology relationships between gene products now should progress beyond primary sequence and "splicing orthology", consisting in ancestrally shared exon-intron structures, is required to define orthologous isoforms at transcript level.ResultsAs a starting step in this direction, in this work we performed a large scale human- mouse gene comparison with a twofold goal: first, to assess if and to which extent traditional gene annotations such as RefSeq capture genuine splicing orthology; second, to provide a more detailed annotation and quantification of true human-mouse orthologous transcripts defined as transcripts of orthologous genes exhibiting the same splicing patterns.ConclusionsWe observed an identical exon/intron structure for 32% of human and mouse orthologous genes. This figure increases to 87% using less stringent criteria for gene structure similarity, thus implying that for about 13% of the human RefSeq annotated genes (and about 25% of the corresponding transcripts) we could not identify any mouse transcript showing sufficient similarity to be confidently assigned as a splicing ortholog. Our data suggest that current gene and transcript data may still be rather incomplete - with several splicing variants still unknown. The observation that alternative splicing produces large numbers of alternative transcripts and proteins, some of them conserved across species and others truly species-specific, suggests that, still maintaining the conventional definition of gene orthology, a new concept of "splicing orthology" can be defined at transcript level.

Spatio-temporal patterns of Hox paralog group 3–6 gene expression during Japanese medaka ( Oryzias latipes) embryonic development

Clustered Hox genes encode transcription factors that pattern the regional identities of tissues along the anterior–posterior (A-P) axis of animals during embryonic development. They are expressed along the A-P axis collinear with their physical location within a cluster. Several studies have examined the expression of teleost Hox genes from paralog groups (PG) 1-4 in the rhombomeres of the hindbrain and the anterior pharyngeal arches. However, little is known about Hox gene expression within the posterior pharyngeal arches (PA3-7) of teleosts. Here we present the spatio-temporal expression patterns of Hox paralog group (PG) 3-6 in the neural tube and posterior arches of the Japanese medaka ( Oryzias latipes). We show that medaka Hox gene expression patterns in the hindbrain are divergent spatially from orthologous genes in mouse and other evolutionarily divergent teleosts, which suggests divergence of cis-regulatory sequences directing hindbrain expression. Further, our study is the first to show the complete teleost Hox PG3-6 expression code in the posterior arches up to the chondrogenic stage of the cranio-facial skeletal elements. This study will provide the basis for comparative teleost Hox gene expression profiles in PA3-7 and may help in understanding the mechanisms underlying development of divergent morphological pharyngeal arch skeletal structures among evolutionarily divergent teleosts.

Altered Function of the SCN1A Voltage-gated Sodium Channel Leads to γ-Aminobutyric Acid-ergic (GABAergic) Interneuron Abnormalities

Voltage-gated sodium channels are required for the initiation and propagation of action potentials. Mutations in the neuronal voltage-gated sodium channel SCN1A are associated with a growing number of disorders including generalized epilepsy with febrile seizures plus (GEFS+),(7) severe myoclonic epilepsy of infancy, and familial hemiplegic migraine. To gain insight into the effect of SCN1A mutations on neuronal excitability, we introduced the human GEFS+ mutation SCN1A-R1648H into the orthologous mouse gene. Scn1a(RH/RH) mice homozygous for the R1648H mutation exhibit spontaneous generalized seizures and premature death between P16 and P26, whereas Scn1a(RH/+) heterozygous mice exhibit infrequent spontaneous generalized seizures, reduced threshold and accelerated propagation of febrile seizures, and decreased threshold to flurothyl-induced seizures. Inhibitory cortical interneurons from P5-P15 Scn1a(RH/+) and Scn1a(RH/RH) mice demonstrated slower recovery from inactivation, greater use-dependent inactivation, and reduced action potential firing compared with wild-type cells. Excitatory cortical pyramidal neurons were mostly unaffected. These results suggest that this SCN1A mutation predominantly impairs sodium channel activity in interneurons, leading to decreased inhibition. Decreased inhibition may be a common mechanism underlying clinically distinct SCN1A-derived disorders.

Homozygosity Mapping Reveals Mutations of GRXCR1 as a Cause of Autosomal-Recessive Nonsyndromic Hearing Impairment

We identified overlapping homozygous regions within the DFNB25 locus in two Dutch and ten Pakistani families with sensorineural autosomal-recessive nonsyndromic hearing impairment (arNSHI). Only one of the families, W98-053, was not consanguineous, and its sibship pointed toward a reduced critical region of 0.9 Mb. This region contained the GRXCR1 gene, and the orthologous mouse gene was described to be mutated in the pirouette (pi) mutant with resulting hearing loss and circling behavior. Sequence analysis of the GRXCR1 gene in hearing-impaired family members revealed splice-site mutations in two Dutch families and a missense and nonsense mutation, respectively, in two Pakistani families. The splice-site mutations are predicted to cause frameshifts and premature stop codons. In family W98-053, this could be confirmed by cDNA analysis. GRXCR1 is predicted to contain a GRX-like domain. GRX domains are involved in reversible S-glutathionylation of proteins and thereby in the modulation of activity and/or localization of these proteins. The missense mutation is located in this domain, whereas the nonsense and splice-site mutations may result in complete or partial absence of the GRX-like domain or of the complete protein. Hearing loss in patients with GRXCR1 mutations is congenital and is moderate to profound. Progression of the hearing loss was observed in family W98-053. Vestibular dysfunction was observed in some but not all affected individuals. Quantitative analysis of GRXCR1 transcripts in fetal and adult human tissues revealed a preferential expression of the gene in fetal cochlea, which may explain the nonsyndromic nature of the hearing impairment.