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Biomedical subjects

Yoichi Gondo

Publications and source records attributed to Yoichi Gondo.

11 recordsLinked to original sources
PubMed2006

A series of ENU-induced single-base substitutions in a long-range cis-element altering Sonic hedgehog expression in the developing mouse limb bud.

Mammal-fish-conserved-sequence 1 (MFCS1) is a highly conserved sequence that acts as a limb-specific cis-acting regulator of Sonic hedgehog (Shh) expression, residing 1 Mb away from the Shh coding sequence in mouse. Using gene-driven screening of an ENU-mutagenized mouse archive, we obtained mice with three new point mutations in MFCS1: M101116, M101117, and M101192. Phenotype analysis revealed that M101116 mice exhibit preaxial polydactyly and ectopic Shh expression at the anterior margin of the limb buds like a previously identified mutant, M100081. In contrast, M101117 and M101192 show no marked abnormalities in limb morphology. Furthermore, transgenic analysis revealed that the M101116 and M100081 sequences drive ectopic reporter gene expression at the anterior margin of the limb bud, in addition to the normal posterior expression. Such ectopic expression was not observed in the embryos carrying a reporter transgene driven by M101117. These results suggest that M101116 and M100081 affect the negative regulatory activity of MFCS1, which suppresses anterior Shh expression in developing limb buds. Thus, this study shows that gene-driven screening for ENU-induced mutations is an effective approach for exploring the function of conserved, noncoding sequences and potential cis-regulatory elements.

Animals↗
PubMed2006

Decreased mutant frequency in embryonic brain of DNA polymerase beta null mice.

DNA polymerase beta (Polbeta) knockout mouse embryos exhibit extensive apoptosis in postmitotic neuronal cells and die immediately after birth. In contrast, no apoptosis has been observed in other tissues as well as liver in the mutant embryos. To study the relationship of Polbeta deficiency and mutagenesis during development and neurogenesis, we examined spontaneous mutations in Polbeta null (Polbeta-/-) and wild-type (Polbeta+/+) mouse embryos, by using the transgenic mutation detection system consisting of a pSSW shuttle vector with the Escherichia coli rpsL reporter gene. Unexpectedly, we found a significant decrease in the mutant frequency of Polbeta-/- brain (1.63+/-0.67x10(-5)) compared with wild-type controls (3.12+/-0.83x10(-5)) (P<0.001). In contrast, no such difference was found between livers from Polbeta-/- (0.92+/-0.38x10(-5)) and wild-type (0.71+/-0.31x10(-5)) embryos. Analysis of mutation spectra revealed that mutations in brains from the two genotypes were almost exclusively single-base deletions and that these sites fell within runs of 2-6 identical bases and a two base repeat in the rpsL sequence, while mutations in the corresponding livers contained base substitutions as well as single-base deletions. Taken together with the extensive neuronal apoptosis associated with Polbeta deficiency, we suggest that the lower mutant frequency observed in Polbeta-/- embryonic brain may be caused by the elimination of neuronal cells with unrepaired DNA damage through apoptosis.

Animals↗
PubMed2005

Implementation of the modified-SHIRPA protocol for screening of dominant phenotypes in a large-scale ENU mutagenesis program.

SHIRPA is a three-stage protocol for the comprehensive assessment of primarily mouse behavior. The first stage consists of high-throughput phenotyping of 33 behavioral observations and 7 metabolic or disease observations. We modified this part of the protocol by integrating new morphologic observations into the initial phenotype assay of behavior and dysmorphology. Behavioral observations assessed by this protocol, now referred to as the "modified-SHIRPA," are compatible with the original "SHIRPA" protocol. Using modified-SHIRPA, we screened dominant phenotypes of more than 10,000 G(1) progeny generated by crossing DBA/2J females with ENU-treated C57BL/6J males. To date, we have obtained 136 hereditary-confirmed mutants that exhibit behavioral and morphologic defects. Some independent mutant lines exhibited similar phenotypes, suggesting that they may represent alleles of the same gene or mutations in the same genetic pathway. They could hold great potential for the unraveling of the molecular mechanisms of certain phenotypes.

Animals↗
PubMed2005

Molecular characterization of ENU mouse mutagenesis and archives.

The large-scale mouse mutagenesis with ENU has provided forward-genetic resources for functional genomics. The frozen sperm archive of ENU-mutagenized generation-1 (G1) mice could also provide a "mutant mouse library" that allows us to conduct reverse genetics in any particular target genes. We have archived frozen sperm as well as genomic DNA from 9224 G1 mice. By genome-wide screening of 63 target loci covering a sum of 197 Mbp of the mouse genome, a total of 148 ENU-induced mutations have been directly identified. The sites of mutations were primarily identified by temperature gradient capillary electrophoresis method followed by direct sequencing. The molecular characterization revealed that all the identified mutations were point mutations and mostly independent events except a few cases of redundant mutations. The base-substitution spectra in this study were different from those of the phenotype-based mutagenesis. The ENU-based gene-driven mutagenesis in the mouse now becomes feasible and practical.

Animals↗
PubMed2005

Enamelin (Enam) is essential for amelogenesis: ENU-induced mouse mutants as models for different clinical subtypes of human amelogenesis imperfecta (AI).

Amelogenesis imperfecta (AI) is a group of commonly inherited defects of dental enamel formation, which exhibits marked genetic and clinical heterogeneity. The genetic basis of this heterogeneity is still poorly understood. Enamelin, the affected gene product in one form of AI (AIH2), is an extracellular matrix protein that is one of the components of enamel. We isolated three ENU-induced dominant mouse mutations, M100395, M100514 and M100521, which caused AI-like phenotypes in the incisors and molars of the affected individuals. Linkage analyses mapped each of the three mutations to a region of chromosome 5 that contained the genes encoding enamelin (Enam) and ameloblastin (Ambn). Sequence analysis revealed that each mutation was a single-base substitution in Enam. M100395 (Enam(Rgsc395)) and M100514 (Enam(Rgsc514)) were putative missense mutations that caused S to I and E to G substitutions at positions 55 and 57 of the translated protein, respectively. Enam(Rgsc395) and Enam(Rgsc514) heterozygotes showed severe breakage of the enamel surface, a phenotype that resembled local hypoplastic AI. The M100521 mutation (Enam(Rgsc521)) was a T to A substitution at the splicing donor site in intron 4. This mutation resulted in a frameshift that gave rise to a premature stop codon. The transcript of the Enam(Rgsc521) mutant allele was degraded, indicating that Enam(Rgsc521) is a loss-of-function mutation. Enam(Rgsc521) heterozygotes showed a hypomaturation-type AI phenotype in the incisors, possibly due to haploinsufficiency of Enam. Enam(Rgsc521) homozygotes showed complete loss of enamel on the incisors and the molars. Thus, we report here that the Enam gene is essential for amelogenesis, and that mice with different point mutations at Enam may provide good animal models to study the different clinical subtypes of AI.

Amelogenesis↗
PubMed2004

A series of maturity onset diabetes of the young, type 2 (MODY2) mouse models generated by a large-scale ENU mutagenesis program.

Mutant mouse models are indispensable tools for clarifying the functions of genes and for elucidating the underlying pathogenic mechanisms of human diseases. Currently, several large-scale mutagenesis projects that employ the chemical mutagen N-ethyl-N-nitrosourea (ENU) are underway worldwide. One specific aim of our ENU mutagenesis project is to generate diabetic mouse models. We screened 9375 animals for dominant traits using a clinical biochemical test and thereby identified 11 mutations in the glucokinase (Gk) gene that were associated with hyperglycemia. GK is a key regulator of insulin secretion in the pancreatic beta-cell. Approximately 190 heterozygous mutations in the human GK gene have been reported to cause maturity onset diabetes of the young, type 2 (MODY2). In addition, five mutations have been reported to cause permanent neonatal diabetes mellitus (PNDM) when present on both alleles. The mutations in our 11 hyperglycemic mutants are located at different positions in Gk. Four have also been found in human MODY2 patients, and another mutant bears its mutation at the same location that is mutated in a PNDM patient. Thus, ENU mutagenesis is effective for developing mouse models for various human genetic diseases, including diabetes mellitus. Some of our Gk mutant lines displayed impaired glucose-responsive insulin secretion and the mutations had different effects on Gk mRNA levels and/or the stability of the GK protein. This collection of Gk mutants will be valuable for understanding GK gene function, for dissecting the function of the enzyme and as models of human MODY2 and PNDM.

Amino Acid Sequence↗
PubMed2004

Development and implementation of a database system to manage a large-scale mouse ENU-mutagenesis program.

A mouse ENU-mutagenesis program at RIKEN GSC has been initiated to conduct a large-scale, genome-wide, early- and late-onset phenotypic screen of mutant mice. We screened about a hundred mice every week with a comprehensive set of phenotype assays including behavioral tests based on a modified SHIRPA protocol, blood tests (both clinical biochemical testing and hemogram), and measurement of locomotor activity in their home cages. To manage the entire program, we developed a client/server architecture database system and named it MUSDB (Mutagenesis Universal Support DataBase). It manages mouse husbandry, mating protocols, procedures for ENU injection and phenotypic screens, phenotype inheritance tests, preservation of sperm and organs, and other materials generated during the program. We have implemented MUSDB in quite a large-scale system that includes 150 client computers. It has, helped reduce typographical errors and provided simple and efficient operation via its front-end user interface. It significantly contributed to the communication within and between workgroups in the program and in the accumulation of various phenotypic and inheritance data.

Animals↗
PubMed2004

Phylogenetic conservation of a limb-specific, cis-acting regulator of Sonic hedgehog ( Shh).

Polarized expression of the Sonic hedgehog ( Shh) gene in the posterior mesenchyme is essential for pattern formation in the appendages of higher vertebrates, from teleost fins to tetrapod limb buds. We report on a sequence in intron 5 of the Lmbr1 gene, which resides approximately 1 Mb from the Shh coding region in the mouse genome and is highly conserved among teleost fishes and throughout the tetrapod lineage. Positional cloning revealed that two mouse mutations, Hx and M100081, characterized by mirror-image digit duplication and ectopic anterior Shh expression, have base substitutions in this sequence. Absence of the conserved sequence in limbless reptiles and amphibians and a cis- trans test using the Hx and Shh KO alleles suggest that the sequence is a cis-acting regulator that controls the polarized expression of Shh.

Animals↗
PubMed2002

Unstable transmission of the RS447 human megasatellite tandem repetitive sequence that contains the USP17 deubiquitinating enzyme gene.

The RS447 megasatellite DNA, which maps to human chromosome 4p16.1, is a highly polymorphic conserved tandem repetitive sequence containing a functional deubiquitinating enzyme gene, USP17. To characterize the hypervariability seen in RS447 fully, we have conducted a pedigree analysis of RS447 transmission by high-resolution pulsed-field gel electrophoresis. We have identified 44 distinct alleles in 74 unrelated chromosomes containing 20-103 copies of the 4.7-kb RS447 unit. Five of 60 parent-to-offspring transmissions clearly show changes in copy number, indicating a high frequency (approximately 8.3%) of meiotic instability. Evidence for somatic mosaicism has also been observed. Searches of the database have revealed the presence of minor RS447 sequences mapping to chromosome 8p23, raising the possibility of a rearrangement or transposition of RS447 within the human genome. These results suggest that the unstable nature of RS447 megasatellite DNA gives rise to its hypervariability and may contribute to the structural dynamics of this repetitive DNA in the genome.

Cell Line↗
PubMed2002

Persistent induction of somatic reversions of the pink-eyed unstable mutation in F1 mice born to fathers irradiated at the spermatozoa stage.

Untargeted mutation and delayed mutation are features of radiation-induced genomic instability and have been studied extensively in tissue culture cells. The mouse pink-eyed unstable (p(un)) mutation is due to an intragenic duplication of the pink-eyed dilution locus and frequently reverts back to the wild type in germ cells as well as in somatic cells. The reversion event can be detected in the retinal pigment epithelium as a cluster of pigmented cells (eye spot). We have investigated the reversion p(um) in F1 mice born to irradiated males. Spermatogonia-stage irradiation did not affect the frequency of the reversion in F1 mice. However, 6 Gy irradiation at the spermatozoa stage resulted in an approximately twofold increase in the number of eye spots in the retinal pigment epithelium of F1 mice. Somatic reversion occurred for the paternally derived p(un) alleles. In addition, the reversion also occurred for the maternally derived, unirradiated p(un) alleles at a frequency equal to that for the paternally derived allele. Detailed analyses of the number of pigmented cells per eye spot indicated that the frequency of reversion was persistently elevated during the proliferation cycle of the cells in the retinal pigment epithelium when the male parents were irradiated at the spermatozoa stage. The present study demonstrates the presence of a long-lasting memory of DNA damage and the persistent up-regulation of recombinogenic activity in the retinal pigment epithelium of the developing fetus.

Animals↗