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De novo mutations accumulate with zygotic cell divisions. However, the occurrence of these mutations and the way they are inherited by somatic cells and germ cells remain unclear. Here, we present a novel method to reconstruct cell lineages. We identified mosaic mutations in mice using deep whole-genome sequencing and reconstructed embryonic cell lineages based on the variant allele frequencies of the mutations. The reconstructed trees were confirmed using nuclear transfer experiments and the genotyping of approximately 50 offspring of each tree. The most detailed tree had 32 terminal nodes and showed cell divisions from the fertilized egg to germ cell– and somatic cell–specific lineages, indicating at least five independent cell lineages that would be selected as founders of the primordial germ cells. The contributions of each lineage to germ cells and offspring varied widely. At the emergence of the germ cell–specific lineages, 10–15 embryonic mutations had accumulated, suggesting that the pregastrulation mutation rate is 1.0 mutation per mitosis. Subsequent mutation rates were 0.7 for germ cells and 13.2 for tail fibroblasts. Our results show a new framework to assess embryonic lineages; further, we suggest an evolutionary strategy for preserving heterogeneity owing to postzygotic mutations in offspring.

Cysteine-rich transmembrane bone morphogenetic protein regulator 1 (CRIM1) is a type I transmembrane protein involved in the organogenesis of many tissues via its interactions with growth factors including BMP, TGF-β, and VEGF. In this study, we used whole-exome sequencing and linkage analysis to identify a novel Crim1 mutant allele generated by ENU mutagenesis in mice. This allele is a missense mutation that causes a cysteine-to-serine substitution at position 140, and is referred to as Crim1

TDP-43 (encoded by the gene TARDBP) is an RNA binding protein central to the pathogenesis of amyotrophic lateral sclerosis (ALS). However, how TARDBP mutations trigger pathogenesis remains unknown. Here, we use novel mouse mutants carrying point mutations in endogenous Tardbp to dissect TDP-43 function at physiological levels both in vitro and in vivo. Interestingly, we find that mutations within the C-terminal domain of TDP-43 lead to a gain of splicing function. Using two different strains, we are able to separate TDP-43 loss- and gain-of-function effects. TDP-43 gain-of-function effects in these mice reveal a novel category of splicing events controlled by TDP-43, referred to as "skiptic" exons, in which skipping of constitutive exons causes changes in gene expression. In vivo, this gain-of-function mutation in endogenous Tardbp causes an adult-onset neuromuscular phenotype accompanied by motor neuron loss and neurodegenerative changes. Furthermore, we have validated the splicing gain-of-function and skiptic exons in ALS patient-derived cells. Our findings provide a novel pathogenic mechanism and highlight how TDP-43 gain of function and loss of function affect RNA processing differently, suggesting they may act at different disease stages. Keywords: ALS; cryptic exon; skiptic exon; splicing; TDP-43

The mouse has been widely used as a model organism for studying human diseases and for evaluating drug safety and efficacy. Many diseases and drug effects exhibit tissue specificity that may be reflected by tissue-specific gene-expression profiles. Here we construct a comprehensive mouse transcriptomic BodyMap across 17 tissues of six-weeks old C57BL/6JJcl mice using RNA-seq. We find different expression patterns between protein-coding and non-coding genes. Liver expressed the least complex transcriptomes, that is, the smallest number of genes detected in liver across all 17 tissues, whereas testis and ovary harbor more complex transcriptomes than other tissues. We report a comprehensive list of tissue-specific genes across 17 tissues, along with a list of 4,781 housekeeping genes in mouse. In addition, we propose a list of 27 consistently and highly expressed genes that can be used as reference controls in expression-profiling analysis. Our study provides a unique resource of mouse gene-expression profiles, which is helpful for further biomedical research.

A complex interaction of signalling events, including the Wnt pathway, regulates sprouting of blood vessels from pre-existing vasculature during angiogenesis. Here we show that two distinct mutations in the (uro)chordate-specific gumby (also called Fam105b) gene cause an embryonic angiogenic phenotype in gumby mice. Gumby interacts with disheveled 2 (DVL2), is expressed in canonical Wnt-responsive endothelial cells and encodes an ovarian tumour domain class of deubiquitinase that specifically cleaves linear ubiquitin linkages. A crystal structure of gumby in complex with linear diubiquitin reveals how the identified mutations adversely affect substrate binding and catalytic function in line with the severity of their angiogenic phenotypes. Gumby interacts with HOIP (also called RNF31), a key component of the linear ubiquitin assembly complex, and decreases linear ubiquitination and activation of NF-κB-dependent transcription. This work provides support for the biological importance of linear (de)ubiquitination in angiogenesis, craniofacial and neural development and in modulating Wnt signalling. This study identifies a deubiquitinase (DUB) that specifically recognises and cleaves linear ubiquitin chains, implicating linear (de)ubiquitination in Wnt signalling and angiogenesis; mutations in gumby cause defects in angiogenesis in mice, and structural and biochemical analysis shows that gumby encodes a linear-ubiquitin-specific DUB. The gumby mutation in mice is associated with lethal angiogenic defects in the embryo. Here Sabine Cordes and colleagues show that the gumby gene encodes a deubiquitinase that specifically recognizes and cleaves linear ubiquitin chains and they implicate linear (de)ubiquitination in Wnt signalling and angiogenesis. In humans, gumby-containing deletions on chromosome 5p15.2 are associated with mental retardation and craniofacial anomalies observed in cri du chat syndrome (CdCS) patients. Although not the only gene deleted, gumby might contribute to some CdCS symptoms via its effects on linear deubiquitination. This work identifies gumby and the pathways regulating the deubiquitination–ubiquitination balance as of possible relevance to antiangiogenic therapies.

CRISPR-Cas9 is efficient enough to knock out both alleles directly by introducing out-of-frame mutations. We succeeded in making biallelic on-target frameshift mutations of the endogenous Gli3 gene; however, the GLI3 protein was expressed in all six of the established cell lines carrying homozygous out-of-frame mutations. We developed a dual-tagged expression vector and proved that illegitimate translation (ITL) was the cause of the unexpected Gli3 expression. Thus, gene expression must be examined even if designed on-target out-of-frame sequences are introduced by genome editing. In addition, it is highly recommended to pre-examine the occurrence of ITL in vitro prior to the design and construction of any genome-editing vectors. In vitro assay systems such as the dual-tagged ITL assay system developed in this study should aid the identification and elucidation of ITL-based human diseases and gene expression.

Camurati-Engelmann disease (CED) is a rare sclerosing bone disorder in humans with autosomal dominant inheritance. Mutations in the gene (TGFB1) that encodes transforming growth factor-β1 (TGF-β1) are causative for CED. TGF-β1 signaling is enhanced by the CED-causing mutations. In this study, we performed Tgfb1 mutation screening in an ENU-mutagenized mouse genomic DNA library. We identified a missense mutation in which cysteine was substituted by serine at position 225 (p.C225S), that corresponded to the CED-causing mutation (p.C225R). TGF-β1 mutant protein carrying p.C225S was secreted normally into the extracellular space. Reporter gene assays showed that the p.C225S mutants enhanced TGF-β signaling at the same level as p.C225R mutants. We generated p.C225S homozygous mice and confirmed that the mature TGF-β1 levels in the culture supernatants of the calvarial cells from the homozygotes were significantly higher than those from wild-type mice. Although the skull and femur are sclerotic in CED, these phenotypes were not observed in p.C225S homozygous mice. These results suggest that human and mouse bone tissue react differently to TGF-β1. These findings are useful to pharmacological studies using mouse models in developing drugs that will target TGF-β signaling.

The neoblasts are the only somatic stem cells in planarians possessing pluripotency, and can give rise to all types of cells, including germline cells. Recently, accumulated knowledge about the transcriptome and expression dynamics of various pluripotent somatic stem cells has provided important opportunities to understand not only fundamental mechanisms of pluripotency, but also stemness across species at the molecular level. The neoblasts can easily be eliminated by radiation. Also, by using fluorescence activated cell sorting (FACS), we can purify and collect many neoblasts, enabling identification of neoblast-related genes by comparison of the gene expression level among intact and X-ray-irradiated animals, and purified neoblasts. In order to find such genes, here we employed the high coverage expression profiling (HiCEP) method, which enables us to observe and compare genome-wide gene expression levels between different samples without advance sequence information, in the planarian D. japonica as a model organism of pluripotent stem cell research. We compared expression levels of ~17,000 peaks corresponding to independent genes among different samples, and obtained 102 peaks as candidates. Expression analysis of genes identified from those peaks by in situ hybridization revealed that at least 42 genes were expressed in the neoblasts and in neoblast-related cells that had a different distribution pattern in the body than neoblasts. Also, single-cell PCR analysis of those genes revealed heterogeneous expression of some genes in the neoblast population. Thus, using multidimensional gene expression analyses, we were able to obtain a valuable data set of neoblast-related genes and their expression patterns.

In order to elucidate ultimate biological function of the genome, the model animal system carrying mutations is indispensable. Recently, large-scale mutagenesis projects have been launched in various species. Especially, the mouse is considered to be an ideal model to human because it is a mammalian species accompanied with well-established genetic as well as embryonic technologies. In 1990's, large-scale mouse mutagenesis projects firstly initiated with a potent chemical mutagen, N-ethyl-N-nitrosourea (ENU) by the phenotype-driven approach or forward genetics. The knockout mouse mutagenesis projects with trapping/conditional mutagenesis have then followed as Phase II since 2006 by the gene-driven approach or reverse genetics. Recently, the next-generation gene targeting system has also become available to the research community, which allows us to establish and analyze mutant mice carrying an allelic series of base substitutions in target genes as another reverse genetics. Overall trends in the large-scale mouse mutagenesis will be reviewed in this article particularly focusing on the new advancement of the next-generation gene targeting system. The drastic expansion of the mutant mouse resources altogether will enhance the systematic understanding of the life. The construction of the mutant mouse resources developed by the forward and reverse genetic mutagenesis is just the beginning of the annotation of mammalian genome. They provide basic infrastructure to understand the molecular mechanism of the gene and genome and will contribute to not only basic researches but also applied sciences such as human disease modelling, genomic medicine and personalized medicine.

ROS1-fusion genes, resulting from chromosomal rearrangement, have been reported in 1–2% of human non-small cell lung cancer cases. More than 10 distinct ROS1-fusion genes, including break-point variants, have been identified to date. In this study, to investigate the in vivo oncogenic activities of one of the most frequently detected fusions, CD74-ROS1, as well as another SDC4-ROS1 fusion that has also been reported in several studies, we generated transgenic (TG) mouse strains that express either of the two ROS1-fusion genes specifically in lung alveolar type II cells. Mice in all TG lines developed tumorigenic nodules in the lung, and a few strains of both TG mouse lines demonstrated early-onset nodule development (multiple tumor lesions present in the lung at 2–4 weeks after birth); therefore, these two strains were selected for further investigation. Tumors developed progressively in the untreated TG mice of both lines, whereas those receiving oral administration of an ALK/MET/ROS1 inhibitor, crizotinib, and an ALK/ROS1 inhibitor, ASP3026, showed marked reduction in the tumor burden. Collectively, these data suggest that each of these two ROS1-fusion genes acts as a driver for the pathogenesis of lung adenocarcinoma in vivo. The TG mice developed in this study are expected to serve as valuable tools for exploring novel therapeutic agents against ROS1-fusion-positive lung cancer.

To study the transcriptome of embryonic stem cells, we used a new gene expression profiling method that can measure the expression levels of unknown and rarely expressed transcripts precisely. We detected a total of 33,136 signal peaks representing transcripts in mouse embryonic stem cells, E14. Subsequent random cloning of the peaks suggests that mouse embryonic stem cells express at least 40,000 transcripts, of which about 2,000 are still unknown. In addition, we identified 1,022 noncoding transcripts, several of which change depending on differentiation in gene expression. Our database provides a high-resolution expression profile of E14 cells and is applicable to other mouse embryonic stem cell analyses. It includes most transcription regulation factor-encoding genes and a significant number of unknown and noncoding transcripts.

Mutations in the Recql4 gene are very likely responsible for a subset of Rothmund-Thomson syndrome (RTS) cases, but until now there has been no animal model to confirm this. Knockout mice in which the Recql4 gene is disrupted at exons 5-8 exhibit embryonic lethality at embryonic day 3.5-6.5. We generated a helicase activity-inhibited mouse by deleting exon 13 of Recql4, which is one of the coding exons of the consensus RecQ-helicase domain. This domain is the primary site of mutations that have been identified in RTS patients. The exon 13-deleted Recql4-deficient mice are viable, but exhibit severe growth retardation and abnormalities in several tissues, and embryonic fibroblasts show a defect in cell proliferation. Abnormalities in the Recql4-deficient mice are similar to those in RTS patients, suggesting that defects in the Recql4 gene may indeed be responsible for RTS. We speculate that the loss of Recql4 helicase activity results in the prematurely aged appearance observed in some RecQ helicase diseases.

Background Disrupted-in-schizophrenia 1 (DISC1) is a promising candidate susceptibility gene for psychiatric disorders, including schizophrenia, bipolar disorder and major depression. Several previous studies reported that mice with N-ethyl-N-nitrosourea (ENU)-induced L100P mutation in Disc1 showed some schizophrenia-related behavioral phenotypes. This line originally carried several thousands of ENU-induced point mutations in the C57BL/6 J strain and single nucleotide polymorphisms (SNPs) from the DBA/2 J inbred strain. Methods To investigate the effect of Disc1 L100P, background mutations and SNPs on phenotypic characterization, we performed behavioral analyses to better understand phenotypes of Disc1 L100P mice and comprehensive genetic analyses using whole-exome resequencing and SNP panels to map ENU-induced mutations and strain-specific SNPs, respectively. Results We found no differences in spontaneous or methamphetamine-induced locomotor activity, sociability or social novelty preference among Disc1 L100P/L100P, L100P/+ mutants and wild-type littermates. Whole-exome resequencing of the original G1 mouse identified 117 ENU-induced variants, including Disc1 L100P per se. Two females and three males from the congenic L100P strain after backcrossing to C57BL/6 J were deposited to RIKEN BioResource Center in 2008. We genotyped them with DBA/2 J × C57BL/6 J SNPs and found a number of the checked SNPs still remained. Conclusion These results suggest that causal attribution of the discrepancy in behavioral phenotypes to the Disc1 L100P mutant mouse line existing among different research groups needs to be cautiously investigated in further study by taking into account the effect(s) of other ENU-induced mutations and/or SNPs from DBA/2 J. Electronic supplementary material The online version of this article (doi:10.1186/1744-9081-10-45) contains supplementary material, which is available to authorized users.

Wnt/β-catenin signalling regulates numerous developmental and homeostatic processes. Ctnnb1 (also known as β-catenin) is the only protein that transmits signals from various Wnt ligands to downstream genes. In this study, we report that our newly established mouse strain, which harbours a Cys429 to Ser missense mutation in the β-catenin gene, exhibited specific organ defects in contrast to mice with broadly functioning Wnt/β-catenin signalling. Both homozygous mutant males and females produced normal gametes but were infertile because of abnormal seminal vesicle and vaginal morphogenesis. An ins-TOPGAL transgenic reporter spatiotemporally sustained Wnt/β-catenin signalling during the corresponding organogenesis. Therefore, β-cateninC429S should provide new insights into β-catenin as a universal component of Wnt/β-catenin signal transduction.

Spontaneous germline mutations generate genetic diversity in populations of sexually reproductive organisms and are thus regarded as a driving force of evolution. However, the cause and mechanism remain unclear. 8-oxoguanine (8-oxoG) is a candidate molecule that causes germline mutations, because it makes DNA more prone to mutation and is constantly generated by reactive oxygen species in vivo. We show here that endogenous 8-oxoG caused de novo spontaneous and heritable G to T mutations in mice, which occurred at different stages in the germ cell lineage and were distributed throughout the chromosomes. Using exome analyses covering 40.9 Mb of mouse transcribed regions, we found increased frequencies of G to T mutations at a rate of 2 × 10−7 mutations/base/generation in offspring of Mth1/Ogg1/Mutyh triple knockout (TOY-KO) mice, which accumulate 8-oxoG in the nuclear DNA of gonadal cells. The roles of MTH1, OGG1 and MUTYH are specific for the prevention of 8-oxoG-induced mutation and 99% of the mutations observed in TOY-KO mice were G to T transversions caused by 8-oxoG; therefore, we concluded that 8-oxoG is a causative molecule for spontaneous and inheritable mutations of the germ lineage cells.

Five members of the RecQ helicase family, RECQL, WRN, BLM, RTS and RECQL5, have been found in human and three of them (WRN, BLM and RTS) were disclosed to be the genes responsible for Werner, Bloom and Rothmund-Thomson syndromes, respectively. RECQL5 (RecQ helicase protein-like 5) was isolated as the fifth member of the family in humans through a search of homologous expressed sequence tags. The gene is expressed with at least three alternative splicing products, alpha, beta and gamma. Here, we isolated mouse RECQL5 beta and determined the DNA sequence of full-length cDNA as well as the genome organization and chromosome locus. The mouse RECQL5 beta gene consists of 2949 bp coding 982 amino acid residues. Comparison of amino acid sequence among human (Homo sapiens), mouse (Mus musculus), Drosophila melanogaster and Caenorhabditis elegans RECQL5 beta homologs revealed three portions of highly conserved regions in addition to the helicase domain. Nineteen exons are dispersed over 40 kbp in the genome and all of the acceptor and donor sites for the splicing of each exon conform to the GT/AG rule. The gene is localized to the mouse chromosome 11E2, which has a syntenic relation to human 17q25.2-q25.3 where human RECQL5 beta exists. Our genetic characterizations of the mouse RECQL5 beta gene will contribute to functional studies on the RECQL5 beta products.

Five members of the RecQ helicase family, RECQL, WRN, BLM, RECQL4 and RECQL5 have been identified in humans. WRN and BLM have been demonstrated to be the responsible genes in Werner and Bloom syndromes, respectively. RECQL4 (RecQ helicase protein–like 4) was identified as a fourth member of the human RecQ helicase family bearing the helicase domain, and it was subsequently shown to be the responsible gene in Rothmund–Thomson syndrome. Here, we isolated mouse RECQL4 and determined the DNA sequence of full-length cDNA as well as the genome organization and chromosome locus. The mouse RECQL4 consists of 3651 base pairs coding 1216 amino acid residues and shares 63.4% of identical and 85.8% of homologous amino acid sequences with human RECQL4. The RECQL4 gene was localized to mouse chromosome 15D3 distal-E1 and rat chromosome 7q34 proximal. They were mapped in the region where the conserved linkage homology has been identified between the two species. Twenty-two exons dispersed over 7 kilo base pairs and all of the acceptor and donor sites for splicing of each exon conformed to the GT/AG rule. Our observations regarding mouse RECQL4 gene will contribute to functional studies on the RECQL4 products.

We previously obtained a monoclonal antibody (Th-10a mAb) that recognizes a single 95-kDa mouse nuclear protein (NP95). Immunostaining analyses revealed that the NP95 was specifically stained in the S phase of normal mouse thymocytes. In contrast, mouse T cell lymphoma cells exhibited a constantly high level of NP95 accumulation irrespective of cell stages during the cell cycle. In the present study, we isolated the cDNA encoding the NP95 from a lambdagt-11 cDNA expression library, using the Th-10a mAb. Sequencing of the whole 3.5-kb cDNA revealed that NP95 is a novel nuclear protein with an open reading frame (ORF) consisting of 782 amino acids. The ORF contains a zinc finger motif, a potential ATP/GTP binding site, a putative cyclin A/E-cdk2 phosphorylation site, and the retinoblastoma protein (RB)-binding motif "IXCXE". The chromosomal location of Np95 gene was determined by fluorescence in situ hybridization. Np95 gene locates on mouse Chromosome (Chr) 17DE1.1. and rat Chr 9q11.2-q12.1. Np95 was strongly expressed in the testis, spleen, thymus, and lung tissues, but not in the brain, liver, or skeletal muscles. These results collectively implicate this novel nuclear protein in cell cycle progression and/or DNA replication.

We established the radiosensitive cell line SX9 from mammary carcinoma cell line FM3A. In SX9 cells a defect of DNA-dependent protein kinase (DNA-PK) activity was suggested. Additionally, a complementation test suggested that the SX9 cell line belongs to a x-ray cross-complementing group (XRCC) 7. Isolation and sequence analyses of DNA-dependent protein kinase catalytic subunit (dna-pkcs) cDNA in SX9 cells disclosed nucleotide “T” (9572) to “C” transition causing substitution of amino acid residue leucine (3191) to proline. Interestingly, the mutation occurs in one allele, and transcripts of the dna-pkcs expressed exclusively from mutated allele. V(D)J recombination assay using extrachromosomal vector revealed the defects of not only coding but also signal joint formation. The frequency of the signal joint decreased to approximately one-tenth and the fidelity drastically decreased to 12.2% as compared with the normal cell line. To confirm the responsibility of thedna-pkcs gene for abnormal V(D)J recombination in SX9, the full-length dna-pkcs gene was introduced into SX9. As a result, restoration of V(D)J recombination by wild typedna-pkcs cDNA was observed. SX9 is a noveldna-pkcs-deficient cell line.

The reticulon-4 receptor, encoded by RTN4R, limits axonal sprouting and neural plasticity by inhibiting the outgrowth of neurites. Human association studies have implicated mutations in RTN4R in the development of schizophrenia, including the identification of several rare nonconservative missense mutations of RTN4R in schizophrenia patients. To investigate the effects of missense mutation of the reticulon-4 receptor on phenotypes relevant to schizophrenia, we behaviourally characterized a novel Rtn4r mutant mouse line with an amino acid substitution (R189H) in the Nogo-66 binding site. Behavioural assays included prepulse inhibition of acoustic startle, locomotor activity, social interaction and spatial cognition. When compared with wildtype littermates, Rtn4r mutant mice exhibited greater social preference, which may reflect a social-anxyolitic effect, and a mild impairment in spatial cognition. Given the mild effect of the R189H mutation of Rtn4r on behavioural phenotypes relevant to schizophrenia, our results do not support missense mutation of RTN4R as a strong risk factor in the pathogenesis of schizophrenia.

In this chapter, mutant mouse resources which have been developed by classical genetics as well as by modern large-scale mutagenesis projects are summarized. Various spontaneous and induced mouse mutations have been archived since the rediscovery of Mendel's genetics in 1900. Moreover, genome-wide, large-scale mutagenesis efforts have recently been expanding the available mutant mouse resources. Forward genetics projects using ENU mutagenesis in the mouse were started in the mid-1990s. The widespread adoption of reverse genetics, using knockouts and conditional mutagenesis based on gene-targeting technology, followed. ENU mutagenesis has now evolved to provide a further resource for reverse genetics, with multiple point mutations in a single gene and this new approach is described. Researchers now have various options to obtain mutant mice: point mutations, transgenic mouse strains, and constitutional or conditional knockout mice. The established mutant strains have already contributed to modeling human diseases by elucidating the underlying molecular mechanisms as well as by providing preclinical applications. Examples of mutant mice, focusing on neurological and behavioral models for human diseases, are reviewed. Human diseases caused by a single gene or a small number of major genes have been well modeled by corresponding mutant mice. Current evidence suggests that quantitative traits based on polygenes are likely to be associated with a range of psychiatric diseases, and these are now coming within the range of modeling by mouse mutagenesis.

As a new mouse mutant resource, the RIKEN ENU-based gene-driven mutagenesis system in the mouse has been available to the research community since 2002. By using random base-substitution mutagenesis with ENU, a new reverse genetics infrastructure has been developed as a next-generation gene-targeting system. The construction of a large-scale mutant mouse library and high-throughput mutation discovery systems were the keys making it practically feasible. The RIKEN mutant mouse library consists of ~ 10,000 G1 mice, within which 100-150 mutant strains have been established based on users' requests every year. Use of the system is very simple: users 1) download an application form from our web site and send to us, and 2) design the PCR primers for the target gene. Then, we screen the RIKEN mutant mouse library and report all the detected mutations to the user. From among the allelic series of discovered mutations, users decide which mutant strain(s) to analyze and request the live mutant strain for functional studies of the target gene. Users have been reporting various functional mutations in the RIKEN mutant mouse library: e.g., missense, knockout-type and even functional non-coding mutations. In the near future, next-generation re-sequencing systems should drastically enhance the utility of the ENU-based gene-driven mutagenesis not only for the mouse but also for other species.

By the N-ethyl-N-nitrosourea (ENU)-based gene-driven mutagenesis, it is now possible to obtain allelic series of mutant mouse strains, each of which carries a different base substitution in any target gene. This new reverse genetic tool has become available based on the ENU mutant mouse library. The ENU mutant mouse library consists of dual archives of frozen sperm and corresponding genomic DNA derived from Generation-1 (G1) male mice, each of which carries thousands of ENU-induced base substitutions. Firstly, ENU-induced mutations in the target gene are screened from the genomic DNA archive by using one of the high-throughput mutation discovery systems. The identified mutations are then revived as live mice by the in vitro fertilization (IVF) and embryo transfer (ET) technology. Just like the knockout (KO) mouse system, the revived mutant strains are finally subjected to the three-generation scheme to reveal the gene function(s) of the target gene. This new reverse genetics or "next-generation gene-targeting system" allows us to elucidate the biological roles of the mouse genome in terms of single base-pair effects not only for the protein-coding sequences but also for any genomic sequences.

Abnormal N-methyl-d-aspartate receptor (NMDAR) function has been implicated in the pathophysiology of schizophrenia. d-serine is an important NMDAR modulator, and to elucidate the role of the d-serine synthesis enzyme serine racemase (Srr) in schizophrenia, we identified and characterized mice with an ENU-induced mutation that results in a complete loss of Srr activity and dramatically reduced d-serine levels. Mutant mice displayed behaviors relevant to schizophrenia, including impairments in prepulse inhibition, sociability and spatial discrimination. Behavioral deficits were exacerbated by an NMDAR antagonist and ameliorated by d-serine or the atypical antipsychotic clozapine. Expression profiling revealed that the Srr mutation influenced several genes that have been linked to schizophrenia and cognitive ability. Transcript levels altered by the Srr mutation were also normalized by d-serine or clozapine treatment. Furthermore, analysis of SRR genetic variants in humans identified a robust association with schizophrenia. This study demonstrates that aberrant Srr function and diminished d-serine may contribute to schizophrenia pathogenesis.

Most biological phenomena, including behavior and metabolic pathways, are governed by an internal clock system that is circadian (i.e., with a period of approximately 24 h) and is reset by light exposure from outside. In order to understand the molecular basis of the resetting mechanism of the clock, we attempted to isolate light-inducible transcripts in the suprachiasmatic nucleus, where the master clock resides, using a new gene expression profiling procedure. We identified 87 such transcripts, successfully cloned 60 of them and confirmed their light inducibility. Six of the 60 were already known to be light inducible and 17 are protein-coding transcripts registered in the public database that were not known to be light inducible. Induction is subjective night specific in most of the transcripts. Interestingly, 6 of the transcripts exhibit rhythmic expression in a circadian manner in the suprachiasmatic nucleus.

The regulatory factor X (RFX) family of transcription factors is characterized by a unique and highly conserved 76-amino acid residue DNA-binding domain. Mammals have five RFX genes, but the physiological functions of their products are unknown, with the exception of RFX5. Here a mouse RFX4 transcript was identified that encodes a peptide of 735 amino acids, including the DNA-binding domain. Its expression was localized in the suprachiasmatic nucleus, the central pacemaker site of the circadian clock. Also, light exposure was found to induce its gene expression in a subjective night-specific manner. Polyclonal antibodies were prepared, and an 80-kDa band was detected in the suprachiasmatic nucleus by Western hybridization. A histochemical study showed a localization of the products in the nucleus. This is the first report on mouse RFX4, which contains the RFX DNA-binding motif. Our investigation may provide clues to the physiological function of RFX4.

We identified the Dexamethasone-induced RAS protein 1 (Dexras1) gene as a cycling gene in the suprachiasmatic nucleus (SCN). Investigation of the whole brain using in situ hybridization demonstrated the localization of the expression of the gene in the SCN, thalamus, piriform cortex and hippocampus. However, rhythmic expression of the gene was observed only in the SCN. The rhythmic change in gene expression during 1 day was approximately five-fold, and the maximum expression was observed during subjective night. Real-time PCR using the SCN, paraventricular nucleus and cortex confirmed these results. Next, we analyzed the expression of the Dexras1 gene in the SCN of cryptochrome (Cry) 1 and 2 double knockout mice. We found that the rhythmic expression disappeared. The results indicate that Dexras1 rhythmicity and levels are dependent upon CRYs. This is the first time that the G protein, which may be involved in the input pathway, has been isolated as a cycling gene in the SCN.

The catalytic subunit of DNA-dependent protein kinase plays critical roles in nonhomologous end joining in repair of DNA double-strand breaks and V(D)J recombination. In addition to the SCID phenotype, it has been suggested that the molecule contributes to the polymorphic variations in radiosensitivity and susceptibility to cancer in mouse strains. Here we show the nucleotide sequence of approximately 193-kbp and 84-kbp genomic regions encoding the entire Prkdc gene (also known as DNA-PKcs) in the mouse and chicken, respectively. A large retroposon was found in intron 51 in the mouse but not in the human or chicken. Comparative analyses of the genome strongly suggested that the region contains only two genes for Prkdc and Mcm4; however, several conserved sequences and cis elements were also predicted.

The effort to elucidate the mechanism of V(D)J recombination has given rise to a dispute as to whether DNA-dependent protein kinase catalytic subunit (DNA-PKcs) contributes to signal joint formation (sjf). Observations reported to date are confusing. Analyses using DNA-PKcs-deficient cells could not conclude the requirement of DNA-PKcs for sjf, because sjf can be formed by end-joining activities which are diverse among cells other than those participating in V(D)J recombination. Here, we observed V(D)J recombination in DNA-PKcs knockout cells and showed that both signal and coding joint formation were clearly impaired in the cells. Subsequently, to directly demonstrate the requirement of DNA-PKcs for sjf, we introduced full-length cDNA of DNA-PKcs into the knockout cells. Furthermore, several mutant DNA-PKcs cDNA constructs designed from mutant cell lines (irs-20, V3, murine scid, and SX9) were also introduced into the cells to obtain further evidence indicating the involvement of DNA-PKcs in sjf. We found as a result that the full-length cDNA complemented the aberrant sjf and that the mutant cDNAs constructs also partially complemented it. Lastly, we looked at whether the kinase activity of DNA-PKcs is necessary for sjf and, as a result, demonstrated a close relationship between them. Our observations clearly indicate that the DNA-PKcs controls not only coding joint formation but also the sjf in V(D)J recombination through its kinase activity.

The gene for the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) is responsible for severe combined immune deficiency (SCID) and its products associate with Ku70/Ku86 autoantigens, c-Abl, and other factors to exert its roles. Investigations to date suggest that DNA-PKcs comprises several regions which specifically interact with these known and other as yet unidentified factors. Nevertheless, the relationship between the structure and function of the DNA-PKcs molecule is poorly understood. Here we report cloning of the entire DNA-PKcs cDNA from chicken and Xenopus laevis. Comparative study of the DNA-PKcs polypeptides from four different vertebrates revealed at least three novel conserved regions in addition to the carboxyl-terminal region containing the phosphatidylinositol-3 kinase domain. We also demonstrated that the four vertebrates share the common genomic organization between a licensing factor, MCM4, and DNA-PKcs, both of which locate in a head-to-head manner within a few kilobase intervals. These data provide useful clues for the further genetic study of this huge multifunctional enzyme.

The DNA-PKcs gene encodes the 465-kDa catalytic subunit of DNA-dependent protein kinase (DNA-PK), which associates with heterodimeric autoantigens Ku70 and Ku80 and exhibits protein kinase activity depending on DNA double-strand breaks. The gene is also responsible for the aberration in severe combined immune deficiency (SCID) mice, which exhibit a high sensitivity to ionizing radiation and abnormal DNA rearrangement of immunoglobulin and T cell receptor genes. There is further evidence that DNA-PKcs phosphorylates various proteins involved in DNA replication, transcription, repair, and recombination. Nevertheless the structure/function relationship in this huge molecule is virtually unknown. We determined the exons and introns of the murine DNA-PKcs gene by the long-distance polymerase chain reaction method. The murine DNA-PKcs gene consists of 86 exons distributed in a region of more than 250 kb. The average size of the exons is 140 bp. All the splicing sites conform to the GT/AG rule. The SCID mutation site (Tyr4046) has been identified in exon 85. The genomic structure of the DNA-PKcs gene provides clues for the study of various functional domains in this macromolecule.

The severe combined immune deficiency (SCID) mouse was reported as an animal model for human immune deficiency. Through the course of several studies, the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) gene came to be considered a candidate for the SCID-responsible gene. We isolated an ORF of the murine DNA-PKcs gene from SCID mice and their parent strain C.B-17 mice and determined the DNA sequences. The ORF of the murine DNA-PKcs gene contained 4128-aa residues and had 78.9% homology with the human DNA-PKcs gene. A particularly important finding is that a T to A transversion results in the substitution of termination codon in SCID mice for the Tyr-4046 in C.B-17 mice. No other mutation was detected in the ORF of the gene. The generality of this transversion was confirmed using four individual SCID and wild-type mice. The substitution took place in the phosphatidylinositol 3-kinase domain, and the mutated gene encodes the truncated products missing 83 residues of wild-type DNA-PKcs products. Furthermore, the quantity of DNA-PKcs transcript in wild-type and SCID cells was almost equal. These observations indicate that the DNA-PKcs gene is the SCID-responsible gene itself and that the detected mutation leads to the SCID aberration.

We have developed an AFLP-based gene expression profiling method called 'high coverage expression profiling' (HiCEP) analysis. By making improvements to the selective PCR technique we have reduced the rate of false positive peaks to approximately 4% and consequently the number of peaks, including overlapping peaks, has been markedly decreased. As a result we can determine the relationship between peaks and original transcripts unequivocally. This will make it practical to prepare a database of all peaks, allowing gene assignment without having to isolate individual peaks. This precise selection also enables us to easily clone peaks of interest and predict the corresponding gene for each peak in some species. The procedure is highly reproducible and sensitive enough to detect even a 1.2-fold difference in gene expression. Most importantly, the low false positive rate enables us to analyze gene expression with wide coverage by means of four instead of six nucleotide recognition site restriction enzymes for fingerprinting mRNAs. Therefore, the method detects 70-80% of all transcripts, including non-coding transcripts, unknown and known genes. Moreover, the method requires no sequence information and so is applicable even to eukaryotes for which there is no genome information available.

Comparative sequence analyses have identified highly conserved genomic DNA sequences, including noncoding sequences, between humans and other species. By performing whole-genome comparisons of human and mouse, we have identified 611 conserved noncoding sequences longer than 500 bp, with more than 95% identity between the species. These long conserved noncoding sequences (LCNS) include 473 new sequences that do not overlap with previously reported ultraconserved elements (UCE), which are defined as aligned sequences longer than 200 bp with 100% identity in human, mouse, and rat. The LCNS were distributed throughout the genome except for the Y chromosome and often occurred in clusters within regions with a low density of coding genes. Many of the LCNS were also highly conserved in other mammals, chickens, frogs, and fish; however, we were unable to find orthologous sequences in the genomes of invertebrate species. In order to examine whether these conserved sequences are functionally important or merely mutational cold spots, we directly measured the frequencies of ENU-induced germline mutations in the LCNS of the mouse. By screening about 40.7 Mb, we found 35 mutations, including mutations at nucleotides that were conserved between human and fish. The mutation frequencies were equivalent to those found in other genomic regions, including coding sequences and introns, suggesting that the LCNS are not mutational cold spots at all. Taken together, these results suggest that mutations occur with equal frequency in LCNS but are eliminated by natural selection during the course of evolution.