RESUMO
Rev7 is a subunit of Polζ, one of the translesion DNA synthesis (TLS) polymerases involved in DNA damage repair. We recently found that Rev7 is also essential for germ cell development in mouse. In the present study, we found the development of ovarian tumors in Rev7 mutant mouse, suggesting the involvement of TLS deficiency in the etiology of ovarian tumor. The Rev7 mutant mice showed complete lack of oocytes and follicles in the ovary. The lack of follicles causes a significant increase of gonadotropin level and an increase in the proliferation of ovarian cells. As a result, the weight of the ovaries of Rev7 mutant mice increased with age and they developed tubulostromal adenomas. However, the remarkable overgrowth of ovaries occurred after gonadotropin level decreases at older ages, suggesting gonadotropin-independent progression of the ovarian tumors. In addition, the Rev7 mutant fibroblasts and ovarian cells showed significant accumulation of DNA damage. These findings suggest that not only increased gonadotropin levels but also lack of DNA damage repair function could be responsible for the development of ovarian tumors in the Rev7 mutant mouse.
Assuntos
Adenoma/genética , Proteínas Mad2/genética , Neoplasias Ovarianas/genética , Adenoma/metabolismo , Adenoma/patologia , Animais , Carcinogênese , Células Cultivadas , Dano ao DNA , Feminino , Fibroblastos/metabolismo , Hormônio Foliculoestimulante/sangue , Hormônio Luteinizante/sangue , Proteínas Mad2/metabolismo , Camundongos Transgênicos , Mutação de Sentido Incorreto , Neoplasias Ovarianas/metabolismo , Neoplasias Ovarianas/patologia , Ovário/metabolismo , Ovário/patologiaRESUMO
The ENU-induced repro57 mutation was identified in an unbiased screen for the discovery of novel genes for fertility. Male repro57 homozygous mice are infertile and exhibit significantly reduced testis weight compared with WT mice. Histological examination of mutant testes revealed that spermatocytes degenerated during late prophase, and no mature spermatozoa were found in the seminiferous epithelium, suggesting that infertility is caused by the arrest of spermatogenesis at late meiotic prophase. Consistent with this hypothesis, the number of foci with MLH1, a protein essential for crossing over, is greatly reduced in repro57 mutant spermatocytes, which also lack chiasmata between homologs and exhibit premature dissociation of XY chromosomes. In repro57 mutant mice, we identified a mutation in the Rnf212 gene, encoding Ring finger protein 212. The overall phenotype of repro57 mice is consistent with the recently reported phenotype of the Rnf212 knockout mice; slight differences may be due to genetic background effects. Thus, the repro57 nonsense mutation provides a new allele of the mouse Rnf212 gene.
Assuntos
Etilnitrosoureia/toxicidade , Infertilidade Masculina/etiologia , Ligases/fisiologia , Meiose/fisiologia , Mutação de Sentido Incorreto/genética , Alquilantes/toxicidade , Animais , Western Blotting , Células Cultivadas , Técnicas Imunoenzimáticas , Infertilidade Masculina/patologia , Masculino , Meiose/efeitos dos fármacos , Camundongos , Camundongos Endogâmicos C3H , Camundongos Endogâmicos C57BL , Camundongos Knockout , RNA Mensageiro/genética , Reação em Cadeia da Polimerase em Tempo Real , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Espermatócitos/citologia , Espermatócitos/efeitos dos fármacos , Espermatócitos/metabolismo , EspermatogêneseRESUMO
The development of the axial skeleton is a complex process, consisting of segmentation and differentiation of somites and ossification of the vertebrae. The autosomal recessive skeletal fusion with sterility (sks) mutation of the mouse causes skeletal malformations due to fusion of the vertebrae and ribs, but the underlying defects of vertebral formation during embryonic development have not yet been elucidated. For the present study, we examined the skeletal phenotypes of sks/sks mice during embryonic development and the chromosomal localization of the sks locus. Multiple defects of the axial skeleton, including fusion of vertebrae and fusion and bifurcation of ribs, were observed in adult and neonatal sks/sks mice. In addition, we also found polydactyly and delayed skull ossification in the sks/sks mice. Morphological defects, including disorganized vertebral arches and fusions and bifurcations of the axial skeletal elements, were observed during embryonic development at embryonic day 12.5 (E12.5) and E14.5. However, no morphological abnormality was observed at E11.5, indicating that defects of the axial skeleton are caused by malformation of the cartilaginous vertebra and ribs at an early developmental stage after formation and segmentation of the somites. By linkage analysis, the sks locus was mapped to an 8-Mb region of chromosome 4 between D4Mit331 and D4Mit199. Since no gene has already been identified as a cause of malformation of the vertebra and ribs in this region, the gene responsible for sks is suggested to be a novel gene essential for the cartilaginous vertebra and ribs.
Assuntos
Padronização Corporal/genética , Infertilidade/genética , Mutação , Costelas/anormalidades , Costelas/embriologia , Coluna Vertebral/anormalidades , Coluna Vertebral/embriologia , Animais , Mapeamento Cromossômico , Cromossomos de Mamíferos/genética , Feminino , Gametogênese/genética , Genes Recessivos/genética , Masculino , Camundongos , Camundongos Mutantes , Fenótipo , EsqueletoRESUMO
Repro22 is a mutant mouse produced via N-ethyl-N-nitrosourea-induced mutagenesis that shows sterility with germ cell depletion caused by defective proliferation of primordial germ cells, decreased body weight, and partial lethality during embryonic development. Using a positional cloning strategy, we identified a missense mutation in Rev7/Mad2l2 (Rev7(C70R)) and confirmed that the mutation is the cause of the defects in repro22 mice through transgenic rescue with normal Rev7. Rev7/Mad2l2 encodes a subunit of DNA polymerase ζ (Polζ), 1 of 10 translesion DNA synthesis polymerases known in mammals. The mutant REV7 did not interact with REV3, the catalytic subunit of Polζ. Rev7(C70R/C70R) cells showed decreased proliferation, increased apoptosis, and arrest in S phase with extensive γH2AX foci in nuclei that indicated accumulation of DNA damage after treatment with the genotoxic agent mitomycin C. The Rev7(C70R) mutation does not affect the mitotic spindle assembly checkpoint. These results demonstrated that Rev7 is essential in resolving the replication stalls caused by DNA damage during S phase. We concluded that Rev7 is required for primordial germ cell proliferation and embryonic viability and development through the translesion DNA synthesis activity of Polζ preserving DNA integrity during cell proliferation, which is required in highly proliferating embryonic cells.
Assuntos
Dano ao DNA , DNA Polimerase II/metabolismo , Proteínas Mad2/metabolismo , Mitomicina/farmacologia , Mutação de Sentido Incorreto , Inibidores da Síntese de Ácido Nucleico/farmacologia , Animais , Apoptose/efeitos dos fármacos , Apoptose/genética , Pontos de Checagem do Ciclo Celular/efeitos dos fármacos , Pontos de Checagem do Ciclo Celular/genética , Proliferação de Células/efeitos dos fármacos , DNA Polimerase II/genética , DNA Polimerase Dirigida por DNA/genética , DNA Polimerase Dirigida por DNA/metabolismo , Feminino , Células Germinativas/citologia , Células Germinativas/metabolismo , Proteínas Mad2/genética , Masculino , Camundongos , Camundongos Mutantes , Proteínas de Ligação a Poli-ADP-Ribose , Fase S/efeitos dos fármacos , Fase S/genética , Fuso Acromático/genética , Fuso Acromático/metabolismoRESUMO
Skeletal fusions with sterility (sks) is an autosomal recessive mutation of mouse that results in male and female sterility because of defects in gametogenesis. The mutants also have skeletal malformations with fused vertebrae and ribs. We examined testicular phenotypes of sks/sks mice to investigate the defects in spermatogenesis. Histological and immunocytochemical analyses and expression analyses of the marker genes demonstrated that spermatogenesis is arrested at mid to late pachytene stage of meiotic prophase with defective synapsis of the homologous chromosomes. Next, we determined the precise chromosomal localization of the sks locus on a 0.3-Mb region of mouse chromosome 4 by linkage analysis. By sequencing the positional candidate genes in this region and whole exome sequencing, we found a GG to TT nucleotide substitution in exon 6 of the Tmem48 gene that encodes a putative transmembrane protein with six transmembrane domains. The nucleotide substitution causes aberrant splicing, which deletes exon 6 of the Tmem48 transcript. Specific expression of TMEM48 was observed in germ cells of males and females. Furthermore, the phenotypes of the sks mutant were completely rescued by the transgenesis of a genomic fragment containing the wild-type Tmem48 gene. These findings indicate that the Tmem48 mutation is responsible for the gametogenesis defects and skeletal malformations in the sks mice. The TMEM48 protein is a nuclear membrane protein comprising the nuclear pore complex; its exact function in the nuclear pore complex is still unknown. Our finding suggested that the nuclear pore complex plays an important role in mammalian gametogenesis and skeletal development.
Assuntos
Doenças Ósseas , Doenças Genéticas Inatas , Infertilidade Feminina , Infertilidade Masculina , Complexo de Proteínas Formadoras de Poros Nucleares , Espermatogênese/genética , Animais , Doenças Ósseas/genética , Doenças Ósseas/metabolismo , Doenças Ósseas/patologia , Pareamento Cromossômico/genética , Análise Mutacional de DNA , Feminino , Doenças Genéticas Inatas/genética , Doenças Genéticas Inatas/metabolismo , Doenças Genéticas Inatas/patologia , Loci Gênicos , Infertilidade Feminina/genética , Infertilidade Feminina/metabolismo , Infertilidade Feminina/patologia , Infertilidade Masculina/genética , Infertilidade Masculina/metabolismo , Infertilidade Masculina/patologia , Masculino , Camundongos , Camundongos Mutantes , Complexo de Proteínas Formadoras de Poros Nucleares/genética , Complexo de Proteínas Formadoras de Poros Nucleares/metabolismo , Mutação PuntualRESUMO
Oocyte meiosis is arrested at prophase I by factors secreted from surrounding somatic cells after oocytes acquire meiotic competence at an early antral stage, and meiosis resumes in preovulatory follicles as a result of the luteinizing hormone (LH) surge. Recently, signaling by C-type natriuretic peptide (CNP) through its receptor, natriuretic peptide receptor 2 (NPR2), was found to be essential for meiotic arrest at the late antral stage. Whether or not CNP/NPR2 signaling maintains oocyte meiotic arrest in earlier follicular stages and how it is associated with meiotic resumption induced by the LH surge is unclear. In this study, we examined the expression of Nppc and Npr2, respectively encoding CNP and NPR2, in the ovaries of immature mice. Nppc and Npr2 mRNA were specifically expressed in the outer and inner granulosa cell layers, respectively, in early antral follicles. Histological analysis of mice with a mutation in Npr2 revealed precocious resumption of oocyte meiosis in early antral follicles. Ovaries of mice treated with excess human chorionic gonadotropin (hCG) exhibited markedly decreased Nppc mRNA levels in granulosa cells of preovulatory follicles. Moreover, we found that amphiregulin, a mediator of LH/hCG activity through epidermal growth factor receptor (EGFR), suppressed Nppc mRNA levels in cultured granulosa cells. These results suggest that CNP/NPR2 signaling is essential for oocyte meiotic arrest in early antral follicles and that activated LH/amphiregulin/EGFR signaling pathway suppresses this signal by downregulating Nppc expression.
Assuntos
Receptores ErbB/metabolismo , Células da Granulosa/metabolismo , Peptídeo Natriurético Tipo C/metabolismo , Folículo Ovariano/metabolismo , Receptores do Fator Natriurético Atrial/metabolismo , Anfirregulina , Animais , Células Cultivadas , Gonadotropina Coriônica/farmacologia , Família de Proteínas EGF , Feminino , Glicoproteínas/metabolismo , Gonadotropinas/farmacologia , Células da Granulosa/efeitos dos fármacos , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Hormônio Luteinizante/metabolismo , Meiose/efeitos dos fármacos , Prófase Meiótica I , Camundongos , Camundongos Endogâmicos C57BL , Peptídeo Natriurético Tipo C/biossíntese , Peptídeo Natriurético Tipo C/genética , Oócitos/metabolismo , Folículo Ovariano/fisiologia , Ovulação/fisiologia , RNA Mensageiro/biossíntese , RNA Mensageiro/efeitos dos fármacos , Receptores do Fator Natriurético Atrial/biossíntese , Receptores do Fator Natriurético Atrial/genética , Transdução de SinaisRESUMO
Development of the male gonads is a complex process with interaction of various cells in the gonads including germ, Sertoli, Leydig, and myoid cells. TF is a mutant rat strain showing male pseudohermaphroditism, with agenesis of Leydig cells and androgen deficiency controlled by an autosomal single recessive gene (mp). The mp locus was mapped on the distal region of rat chromosome 7 by linkage analysis, but the gene responsible for the mp mutation has not been identified. In this study, we performed fine linkage mapping and sequence analysis to determine the causative gene of the mp mutation, and performed an immunohistochemical study using a Leydig cell-specific marker to investigate detailed phenotypes of the mutant rats during the testicular development. As a result, we found a missense mutation of the gene encoding Desert hedgehog (Dhh) in the mutant rat, which could result in loss of function of the DHH signaling pathway. Histochemical examination revealed remarkably reduced number of fetal Leydig cells and lack of typical spindle-shaped adult Leydig cell in the mp/mp rats. These phenotypes resembled those of the Dhh-null mice. Additionally, testosterone levels were significantly lower in the mp/mp fetus, indicating androgen deficiency during embryonic development. These results indicate that the mutation of the Dhh gene may be responsible for the pseudohermaphrodite phenotypes of the mutant rat, and that the Dhh gene is probably essential for the development of Leydig cells.
Assuntos
Transtorno 46,XY do Desenvolvimento Sexual/genética , Proteínas Hedgehog/genética , Células Intersticiais do Testículo/patologia , Mutação de Sentido Incorreto/genética , Testículo/citologia , Animais , Mapeamento Cromossômico , Cromossomos de Mamíferos , Feto/citologia , Feto/metabolismo , Proteínas Hedgehog/metabolismo , Masculino , RNA Mensageiro/genética , Ratos , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Testosterona/deficiênciaRESUMO
repro23 is an autosomal recessive mutation of the mouse generated by the N-ethyl-N-nitrosourea (ENU)-induced mutagenesis program at The Jackson Laboratory. The repro23/repro23 homozygous mouse shows male-specific infertility caused by defective spermatogenesis. In the present study, we investigated the testicular pathology of the affected mouse and performed linkage analysis to determine the chromosomal localization of the repro23 locus. Histological examination of the affected testis showed that the seminiferous epithelium of the repro23/repro23 mice contained spermatogonia and early stage spermatocytes, but no spermatids or spermatozoa. Immunohistochemical staining for Hsc70t, a spermatid specific protein, confirmed the absence of elongating spermatids. These findings indicated interruption of the spermatogenesis during meiosis in the repro23/repro23 mouse. By linkage analysis using 137 affected mice of F(2) progeny obtained from crosses between repro23/repro23 female and JF1/Ms (+/+) male mice, the repro23 locus was mapped to 2.2-Mb region of mouse chromosome 7. Although this region contains several potential candidate genes for the repro23 mutation, no gene already identified as a cause of defective spermatogenesis was in this region. Therefore, the gene responsible for the repro23 mutation is suggested to be a novel gene which plays an essential role in mammalian spermatogenesis.
Assuntos
Alquilantes/farmacologia , Etilnitrosoureia/farmacologia , Ligação Genética/genética , Infertilidade Masculina/genética , Espermatogênese/genética , Animais , Mapeamento Cromossômico , Feminino , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Regulação da Expressão Gênica no Desenvolvimento/genética , Ligação Genética/efeitos dos fármacos , Genitália Masculina/crescimento & desenvolvimento , Proteínas de Choque Térmico HSC70/metabolismo , Homozigoto , Masculino , Camundongos , Camundongos Endogâmicos C3H , Camundongos Endogâmicos C57BL , Camundongos Mutantes , Tamanho do Órgão/genética , Espermatócitos/metabolismo , Espermatócitos/patologia , Espermatogênese/fisiologia , Testículo/metabolismo , Testículo/patologiaRESUMO
BACKGROUND: Koala (Koa) is a dominant mutation in mice causing bushy muzzle and pinna, and is associated with a chromosomal inversion on the distal half of chromosome 15. To identify the gene responsible for the Koa phenotypes, we investigated phenotypes of Koa homozygous mice and determined the breakpoints of the inversion with a genetic method using recombination between two different chromosomal inversions. RESULTS: Skeletal preparation of Koa homozygotes showed marked deformity of the ribs and a wider skull with extended zygomatic arches, in addition to a general reduction in the lengths of long bones. They also had open eyelids at birth caused by a defect in the extension of eyelid anlagen during the embryonic stages. The proximal and distal breakpoints of the Koa inversion were determined to be 0.8-Mb distal to the Trsps1 gene and to 0.1-Mb distal to the Hoxc4 gene, respectively, as previously reported. The phenotypes of mice with the recombinant inverted chromosomes revealed the localization of the gene responsible the Koa phenotype in the vicinity of the proximal recombinant breakpoint. Expression of the Trsps1 gene in this region was significantly reduced in the Koa homozygous and heterozygous embryos. CONCLUSION: While no gene was disrupted by the chromosomal inversion, an association between the Koa phenotype and the proximal recombinant breakpoint, phenotypic similarities with Trps1-deficient mice or human patients with TRSP1 mutations, and the reduced expression of the Trsps1 gene in Koa mice, indicated that the phenotypes of the Koa mice are caused by the altered expression of the Trps1 gene.
Assuntos
Osso e Ossos/anormalidades , Quebra Cromossômica , Inversão Cromossômica , Animais , Cromossomos de Mamíferos , Embrião de Mamíferos/anormalidades , Fatores de Transcrição GATA/genética , Perfilação da Expressão Gênica , Proteínas de Homeodomínio/genética , Camundongos , Camundongos Mutantes/genética , Repetições de Microssatélites , Fenótipo , Proteínas RepressorasRESUMO
Repro22 is an N-ethyl-N-nitrosourea (ENU)-induced mutation in mice showing depletion of both male and female germ cells. In the present study, we investigated the male phenotypes of the mutant mouse at the adult stage. The repro22/repro22 homozygous mice showed reduced body weights as well as markedly reduced testis weights. Histological examination of the testes at 4 and 10 months of age showed no germ cells in the seminiferous tubules of the affected testis while a number of Sertoli cells were observed in the tubules. In addition to the germ cell depletion, the testes of the affected mouse contained expanded intertubular spaces that were filled by Leydig cell-like interstitial cells. These interstitial cells were confirmed to be Leydig cells by immunohistochmical staining using anti-3beta-HSD antibody. The estimated number of Leydig cells in the affected testes at 10 months of age increased approximately 2 fold compared with those of normal testes. Furthermore, the plasma testosterone levels of the affected mice at 10 months of age were significantly higher than those of the normal mice. These findings indicated that the repro22/repro22 mouse developed hyperplasia of Leydig cells that was presumably caused by the absence of germ cells in the seminiferous tubules.
Assuntos
Infertilidade Masculina/genética , Infertilidade Masculina/fisiopatologia , Células Intersticiais do Testículo/patologia , Células Intersticiais do Testículo/fisiologia , Espermatogênese/fisiologia , Alquilantes/toxicidade , Animais , Contagem de Células , Modelos Animais de Doenças , Etilnitrosoureia/toxicidade , Homozigoto , Hiperplasia , Infertilidade Masculina/induzido quimicamente , Masculino , Camundongos , Camundongos Endogâmicos C3H , Camundongos Endogâmicos C57BL , Camundongos Mutantes , Fenótipo , Células de Sertoli/citologia , Espermatozoides/citologia , Testosterona/sangueRESUMO
Repro34 is an N-ethyl-N-nitrosourea (ENU)-induced mutation in mice showing male-specific infertility caused by defective spermatogenesis. In the present study, we investigated pathogenesis and molecular lesions in relation to spermatogenesis in the repro34/repro34 homozygous mouse. Histological examination of the testis showed that the seminiferous epithelium of the repro34/repro34 mouse contained spermatogonia and spermatocytes but no round and elongating spermatids. Instead of these haploid cells, multinucleated giant cells occupied the niche of the seminiferous tubules. Immunohistochemical staining for Hsc70t, an elongating spermatid specific protein, confirmed the absence of elongating spermatids. Furthermore, RT-PCR showed that there were significantly reduced expressions of the marker genes specifically expressed in the spermatid and that there was no difference in the expressions of the spermatocyte specific marker genes. These findings indicated interruption of the spermatogenesis during transition from the spermatocyte to spermatid in the repro34/repro34 mouse. The repro34 locus has been mapped on a 7.0-Mb region of mouse chromosome 5 containing the Syntaxin 2/Epimorphin (Stx2/Epim) gene, and targeted disruption of this gene has been reported to cause defective spermatogenesis. We therefore sequenced the entire coding region of the Stx2/Epim gene and found a nucleotide substitution that results in a nonsense mutation of this gene. The expression pattern of the Stx2/Epim gene during the first wave of spermatogenesis, increased expression at later stages of spermatogenesis, was in agreement with the affected phase of spermatogenesis in the adult repro34/repro34 testis. We therefore concluded that the male infertility of the repro34/repro34 mouse is caused by the interruption of spermatogenesis during transition from the spermatocyte to spermatid and that the nonsense mutation of the Stx2/Epim gene is responsible for the interruption of spermatogenesis.
Assuntos
Códon sem Sentido , Etilnitrosoureia/farmacologia , Glicoproteínas de Membrana/genética , Espermatogênese/genética , Sintaxina 1/genética , Animais , DNA/metabolismo , Células Gigantes/metabolismo , Proteínas de Choque Térmico HSC70/biossíntese , Infertilidade Masculina/genética , Masculino , Camundongos , Camundongos Mutantes , RNA/metabolismo , Espermatócitos/metabolismoRESUMO
Koala (Koa) and hairy ears (Eh) mutations of mice are associated with chromosomal inversions in the distal half of chromosome 15. Since these two mutant mice show some common phenotypic features including extra hair on pinna and craniofacial dysmorphogenesis and have similar inverted regions, we determined the inverted regions of these two chromosomal inversions to examine whether a common gene is responsible for the phenotypes of these two mutants. The inverted regions were identified as the recombination-suppressed regions by linkage analysis. The length of the recombination-suppressed regions of Koa and Eh were approximately 52 and 47 Mb, respectively, and these inverted regions were not the same. These results indicate that the phenotypes of Koa and Eh mutant mice are likely to be caused by different genes.
Assuntos
Inversão Cromossômica/genética , Camundongos Mutantes/genética , Recombinação Genética/genética , Animais , Feminino , Ligação Genética/genética , Masculino , Camundongos , FenótipoRESUMO
The hairy ears (Eh) mutation in the mouse originated from neutron irradiation experiments and is associated with chromosomal inversion on chromosome 15. Eh/+ mice have small pinna and extra hairs on the pinna but the phenotypic features of Eh/Eh mice are unclear. In this study we found that Eh/Eh mice died shortly after birth and had a cleft palate caused by impaired growth of palate shelves. Because genes located on the breakpoints of inversion are likely to be responsible for the defects associated with chromosomal inversions, we determined the breakpoints of the Eh inversion. We used a new genetic method that uses recombinant chromosomes resulting from crossing over between two overlapping inversions to determine the breakpoints. Koa is a mouse mutation associated with inversion of chromosome 15, which partially overlaps with the Eh inversion. We made Eh +/+ Koa double heterozygotes and obtained the recombinant chromosomes possessing deletion and duplication of the regions flanked by the breakpoints of both inversions, which were generated by crossing over within the overlapped region of these inversions. By defining the deleted regions we identified the breakpoints of the Eh inversion. We then examined the expression of genes in the vicinities of the breakpoints and found ectopic expression of the Hoxc5 gene and a transcript with unknown function in the developing palate of Eh/Eh mice, which is likely to be responsible for the cleft palate.
Assuntos
Inversão Cromossômica/genética , Fissura Palatina/genética , Mutação/genética , Animais , Animais Recém-Nascidos , Apoptose , Pareamento de Bases , Proliferação de Células , Quebra Cromossômica , Deleção Cromossômica , Cromossomos de Mamíferos/genética , Fissura Palatina/embriologia , Fissura Palatina/patologia , Troca Genética/genética , Viabilidade Fetal , Regulação da Expressão Gênica , Genótipo , Proteínas de Homeodomínio/genética , Camundongos , Camundongos Mutantes , Fenótipo , RNA Mensageiro/genética , RNA Mensageiro/metabolismoRESUMO
The aspermia mutation of the rat exhibits male sterility caused by arrest of spermatogenesis, which is controlled by an autosomal single recessive gene (as). The as locus has been mapped on rat chromosome 12. We recently identified a causative mutation for the aspermia phenotype of the as homozygous rats in the gene encoding Fkbp6, a member of the immunophilins FK506 binding proteins. In this paper, we report the fine mapping of the as locus by linkage analysis combined with comparative mapping using rat, mouse, and human genomic sequences and expression analysis of genes located in the as region. We constructed a fine linkage map of the region of rat chromosome 12 close to the as locus by using 13 microsatellite markers and localized the as locus to a 1.0-cM interval. Comparison of the linkage map with physical maps of rat, mouse, and human refined the as critical region in a 2.2-Mb segment of the rat physical map between the D12Nas3 and D12Nas8 genes, which includes the Fkbp6 gene. A centromeric part of this segment corresponds to the region commonly deleted in Williams syndrome, a human complex developmental disorder, on human chromosome 7q11.23. The expression analysis of 23 genes located on the 2.2-Mb segments in various mouse tissues identified genes exclusively or strongly expressed in the testis.