翘嘴鲌Sox9基因的克隆及CpG岛甲基化与基因表达的关系

为了揭示翘嘴鲌(Culter alburnus)性别决定与分化的作用机制, 进而更好地发展性别控制育种技术, 研究重点分析了Sox9基因在翘嘴鲌性腺分化过程中的作用。通过RT-PCR和RACE方法获得了翘嘴鲌2个旁系同源基因Sox9a和Sox9b的cDNA序列: Sox9a全长1642 bp, 编码458个氨基酸; Sox9b全长1673 bp, 编码456个氨基酸。序列分析表明两者相似度达到73.95%, 编码HMG盒区域极其保守。蛋白质次级结构预测显示Sox9a和Sox9b除了保守的HMG盒结构域外, 还存在2个核定位信号; 两者的三维结构都存在多个螺旋结构。系统进化树分析发现翘嘴鲌Sox9a与罗非鱼关系最近, 但Sox9b形成单独的一支。利用实时荧光定量PCR技术分析了翘嘴鲌Sox9a和Sox9b基因在各成体组织中的表达水平, 结果显示Sox9a在脑和精巢中表达量最高, 其次是肌肉、鳍条、眼睛和卵巢, 在肾脏、脾脏、肝脏中相对较低; Sox9b只在脑、鳍条、眼睛和精巢中检测到一定水平的表达。通过重亚硫酸氢盐DNA测序方法分析了翘嘴鲌性腺组织Sox9a启动子CpG岛甲基化修饰模式, 结果显示在精巢中CG位点几乎不发生甲基化, 然而卵巢中的甲基化程度非常高。这些结果表明启动子CpG甲基化可以调控Sox9a的性别异形表达, 表观遗传修饰在翘嘴鲌性腺发育过程中可能具有重要的生物学功能。     

Antagonism of the testis- and ovary-determining pathways during ovotestis development in mice

Ovotestis development in B6-XY^POS mice provides a rare opportunity to study the interaction of the testis- and ovary-determining pathways in the same tissue. We studied expression of several markers of mouse fetal testis (SRY, SOX9) or ovary (FOXL2, Rspo1) development in B6-XY^POS ovotestes by immunofluorescence, using normal testes and ovaries as controls. In ovotestes, SOX9 was expressed only in the central region where SRY is expressed earliest, resulting in testis cord formation. Surprisingly, FOXL2-expressing cells also were found in this region, but individual cells expressed either FOXL2 or SOX9, not both. At the poles, even though SOX9 was not up-regulated, SRY expression was down-regulated normally as in XY testes, and FOXL2 was expressed from an early stage, demonstrating ovarian differentiation in these areas. Our data (1) show that SRY must act within a specific developmental window to activate Sox9; (2) challenge the established view that SOX9 is responsible for down-regulating Sry expression; (3) disprove the concept that testicular and ovarian cells occupy discrete domains in ovotestes; and (4) suggest that FOXL2 is actively suppressed in Sertoli cell precursors by the action of SOX9. Together these findings provide important new insights into the molecular regulation of testis and ovary development.     

Identification of SRY‐box 30 as an age‐related essential gatekeeper for male germ‐cell meiosis and differentiation

Although important factors governing the meiosis have been reported in the embryonic ovary, meiosis in postnatal testis remains poorly understood. Herein, we first report that SRY‐box 30 (Sox30) is an age‐related and essential regulator of meiosis in the postnatal testis. Sox30‐null mice exhibited uniquely impaired testis, presenting the abnormal arrest of germ‐cell differentiation and irregular Leydig cell proliferation. In aged Sox30‐null mice, the observed testicular impairments were more severe. Furthermore, the germ‐cell arrest occurred at the stage of meiotic zygotene spermatocytes, which is strongly associated with critical regulators of meiosis (such as Cyp26b1, Stra8 and Rec8) and sex differentiation (such as Rspo1, Foxl2, Sox9, Wnt4 and Ctnnb1). Mechanistically, Sox30 can activate Stra8 and Rec8, and inhibit Cyp26b1 and Ctnnb1 by direct binding to their promoters. A different Sox30 domain required for regulating the activity of these gene promoters, providing a “fail‐safe” mechanism for Sox30 to facilitate germ‐cell differentiation. Indeed, retinoic acid levels were reduced owing to increased degradation following the elevation of Cyp26b1 in Sox30‐null testes. Re‐expression of Sox30 in Sox30‐null mice successfully restored germ‐cell meiosis, differentiation and Leydig cell proliferation. Moreover, the restoration of actual fertility appeared to improve over time. Consistently, Rec8 and Stra8 were reactivated, and Cyp26b1 and Ctnnb1 were reinhibited in the restored testes. In summary, Sox30 is necessary, sufficient and age‐associated for germ‐cell meiosis and differentiation in testes by direct regulating critical regulators. This study advances our understanding of the regulation of germ‐cell meiosis and differentiation in the postnatal testis.     

Demethylation of CpG islands in the 5' upstream regions mediates the expression of the human testis-specific gene MAGEB16 and its mouse homolog Mageb16

Tissue-specific gene expression is regulated by epigenetic modification involving trans-acting factors. Here, we identified that the human MAGEB16 gene and its mouse homolog, Mageb16, are only expressed in the testis. To investigate the mechanism governing their expression, the promoter methylation status of these genes was examined in different samples. Two CpG islands (CGIs) in the 5'' upstream region of MAGEB16 were highly demethylated in human testes, whereas they were methylated in cells without MAGEB16 expression. Similarly, the CGI in Mageb16 was hypomethylated in mouse testes but hypermethylated in other tissues and cells without Mageb16 expression. Additionally, the expression of these genes could be activated by treatment with the demethylation agent 5''-aza-2''-deoxycytidine (5''-aza-CdR). Luciferase assays revealed that both gene promoter activities were inhibited by methylation of the CGI regions. Therefore, we propose that the testis-specific expression of MAGEB16 and Mageb16 is regulated by the methylation status of their promoter regions. [BMB Reports 2014; 47(2): 86-91]     

Sox3 is required for gonadal function, but not sex determination, in males and females

Sox3 is expressed in developing gonads and in the brain. Evolutionary evidence suggests that the X-chromosomal Sox3 gene may be the ancestral precursor of Sry, a sex-determining gene, and Sox3 has been proposed to play a role in sex determination. However, patients with mutations in SOX3 exhibit normal gonadal determination but are mentally retarded and have short stature secondary to growth hormone (GH) deficiency. We used Cre-LoxP targeted mutagenesis to delete Sox3 from mice. Null mice of both sexes had no overt behavioral deficits and exhibited normal GH gene expression. Low body weight was observed for some mice; overgrowth and misalignment of the front teeth was observed consistently. Female Sox3 null mice (-/-) developed ovaries but had excess follicular atresia, ovulation of defective oocytes, and severely reduced fertility. Pituitary (luteinizing hormone and follicle-stimulating hormone) and uterine functions were normal in females. Hemizygous male null mice (-/Y) developed testes but were hypogonadal. Testis weight was reduced by 42%, and there was extensive Sertoli cell vacuolization, loss of germ cells, reduced sperm counts, and disruption of the seminiferous tubules. We conclude that Sox3 is not required for gonadal determination but is important for normal oocyte development and male testis differentiation and gametogenesis.     

Investigation of the fate of Sry-expressing cells using an in vivo Cre/loxP system

Sry (sex-determining region on Y chromosome) is expressed in the undifferentiated, bipotential genital ridges of mammalian XY fetuses. The expression of Sry initiates testis development, but the lineage of Sry-expressing cells is unclear. In this study, double-transgenic mice were analyzed using the Cre/loxP system. Cre under the control of the Sry promoter was expressed in the fetal gonads of transgenic mice similarly to endogenous Sry. The Sry/Cre-transgenic mice were crossed with CAG(cytomegalovirus immediate-early enhancer, chicken beta-actin promoter and fusion intron of chicken beta-actin and rabbit beta-globin)/loxP/CAT/loxP/LacZ-transgenic mice, in which the transgene expressed beta-galactosidase after a Cre-mediated recombination event. Sertoli cells, germ cells of testes and granulosa cells of ovaries of double-transgenic mice stained positive with X-gal. Cre expression was detected in germ cells and peritubular/Sertoli cells in adult testes. It is not clear whether beta-galactosidase expression in the Sertoli cells of the testes occurred as a result of Cre expression in the adult or in the fetal gonads. These analyses indicate that cells expressing Sry-inducing factors in female fetal gonads become granulosa cells.     

In Vitro Spermatogenesis in Explanted Adult Mouse Testis Tissues

Research on in vitro spermatogenesis is important for elucidating the spermatogenic mechanism. We previously developed an organ culture method which can support spermatogenesis from spermatogonial stem cells up to sperm formation using immature mouse testis tissues. In this study, we examined whether it is also applicable to mature testis tissues of adult mice. We used two lines of transgenic mice, Acrosin-GFP and Gsg2-GFP, which carry the marker GFP gene specific for meiotic and haploid cells, respectively. Testis tissue fragments of adult GFP mice, aged from 4 to 29 weeks old, which express GFP at full extension, were cultured in medium supplemented with 10% KSR or AlbuMAX. GFP expression decreased rapidly and became the lowest at 7 to 14 days of culture, but then slightly increased during the following culture period. This increase reflected de novo spermatogenesis, confirmed by BrdU labeling in spermatocytes and spermatids. We also used vitamin A-deficient mice, whose testes contain only spermatogonia. The testes of those mice at 13-21 weeks old, showing no GFP expression at explantation, gained GFP expression during culturing, and spermatogenesis was confirmed histologically. In addition, the adult testis tissues of Sl/Sl^d mutant mice, which lack spermatogenesis due to Kit ligand mutation, were cultured with recombinant Kit ligand to induce spermatogenesis up to haploid formation. Although the efficiency of spermatogenesis was lower than that of pup, present results showed that the organ culture method is effective for the culturing of mature adult mouse testis tissue, demonstrated by the induction of spermatogenesis from spermatogonia to haploid cells.     

Homozygous inactivation of Sox9 causes complete XY sex reversal in mice

In the presence of the Y-chromosomal gene Sry, the bipotential mouse gonads develop as testes rather than as ovaries. The autosomal gene Sox9, a likely and possibly direct Sry target, can induce testis development in the absence of Sry. Sox9 is thus sufficient but not necessarily essential for testis induction. Mutational inactivation of one allele of SOX9/Sox9 causes sex reversal in humans but not in mice. Because Sox9(-/-) embryos die around Embryonic Day 11.5 (E11.5) at the onset of testicular morphogenesis, differentiation of the mutant XY gonad can be analyzed only ex vivo in organ culture. We have therefore conditionally inactivated both Sox9 alleles in the gonadal anlagen using the CRE/loxP recombination system, whereby CRE recombinase is under control of the cytokeratin 19 promoter. Analysis of resulting Sox9(-/-) XY gonads up to E15.5 reveals immediate, complete sex reversal, as shown by expression of the early ovary-specific markers Wnt4 and Foxl2 and by lack of testis cord and Leydig cell formation. Sry expression in mutant XY gonads indicates that downregulation of Wnt4 and Foxl2 is dependent on Sox9 rather than on Sry. Our results provide in vivo proof that, in contrast to the situation in humans, complete XY sex reversal in mice requires inactivation of both Sox9 alleles and that Sox9 is essential for testogenesis in mice.