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.

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 spindleshaped 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.

Background: Rev7 encodes a subunit of Pol for translesion DNA synthesis (TLS). Results: We found a Rev7 mutation in mice that causes developmental defects and increases susceptibility for genotoxicity. Conclusion: Rev7 is essential for mouse development through its function in cell proliferation.Significance: These findings demonstrate a unique function of Pol in development that is absent in other TLS polymerases.

Abstract.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. Key words: ENU mutagenesis, Infertility, Mouse, Mutation, Spermatogenesis, Syntaxin 2/Epimorphin (Stx2/Epim) gene (J. Reprod. Dev. 54: [122][123][124][125][126][127][128] 2008) ammalian spermatogenesis is one of the most dynamic proc e s s e s o f c e l l p r o l i f e r a t i o n , d i f f e r e n t i a t i o n a n d morphogenesis and involves numerous cellular and molecular steps. In order to understand the mechanisms underlying mammal i a n s p e r m a t o g e n e s i s , a n i m a l m o d e l s w i t h d e f e c t i v e spermatogenesis are essential tools to identify the signaling pathways and molecules involved in regulation of spermatogenesis [1,2]. So far, a large number of infertile genetic animal models have been established by spontaneous mutations and gene targeting technologies [2]. These animal models have contributed to understanding of the mechanisms involved in mammalian spermatogenesis [1][2][3][4][5][6]. They are also valuable for better understanding of the pathogenesis of human male infertility, which is mostly caused by defe...

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.

Background: sks is a mouse mutant showing sterility caused by defects in meiosis. Results: We found a mutation of the Tmem48 gene encoding nuclear pore complex protein. The mutation causes aberrant splicing, resulting in deletion of an exon. Conclusion: Tmem48 is essential for meiosis and gametogenesis. Significance: This is the first report to demonstrate that the nuclear pore complex has an important role in mammalian gametogenesis.

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 to wild type. 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 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 mouse is consistent with the recently reported phenotype of the Rnf212 knockout mouse; slight differences may be due to genetic background effects. Thus, the repro57 nonsense mutation provides a new allele of the mouse Rnf212 gene.

Abstract.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-3β-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. Key words: ENU mutagenesis, Germ cell, Infertility, Leydig cell, Mouse, Testosterone (J. Reprod. Dev. 54: [225][226][227][228] 2008) nfertility is a major health problem worldwide that influences more than 10% of couples, and approximately 50% of cases of infertility are caused by male factors. In particular, Sertoli cellonly syndrome, a form of non-obstructive azoospermia, is the most serious male infertility, as patients with this disorder show germ cell depletion and are untreatable using assisted reproduction techniques. Although a significant portion of male infertilities is believed to be caused by autosomal recessive mutations [1], the genetic factors that underlay most nonsyndromic male infertilities have not yet been identified, with a few exceptions [2,3]. Mutant mice established by gene targeting technology, chemical mutagenesis and spontaneous mutations [4][5][6][7], showing various features of infertility are expected to be useful animal models for investigating the pathogenesis and genetic factors of human infertilities. However, only a limited number of mouse models for Sertoli cell-only syndrome or germ cell depletion have been reported [8][9][10][11]. Repro22 is a mutation in mice recently produced by N-ethyl-Nnitrosourea (ENU)-induced mutagenesis at The Jackson Laboratory, showing depletion of germ cells in both the male and female. In the present study, we investigated male phenotypes of the mutant mouse at the adult stage and found that the mutant mouse showed Leydig cell hyperplasia and an elevated plasma testosterone level in addition to germ cell depletion. Materials and MethodsThe mice bearing the repro22 mutation were produced and provided by the ReproGenomics Program at The Jackson Laboratory. The mice have a mixed g...