Mammalian Gonadogenesis, Folliculogenesis and Fertilization

小鼠妊娠期超过20天。在第7.25天的小鼠胚胎中首次检测到生殖细胞，在第13天，XX雌性动物从胚外尿囊迁移到生殖嵴，在生殖嵴处原始性腺分化为卵巢。利用高通量测序和现代信息学技术筛选泌尿生殖系统cDNA文库，我们已经确定了一个新的基因位于X染色体上。该基因，命名为Nt 2，在性别决定时优先在雌性性腺的体细胞中表达。所得蛋白质在其羧基末端附近含有同源异型框结构域，这提高了NT 2可能在性腺发生中发挥作用的可能性。该基因已成功地在胚胎干细胞中靶向，目前正用于建立小鼠品系，以分析无效表型。出生时，卵巢含有完整的生殖细胞，每个生殖细胞被单层颗粒细胞包围，颗粒细胞共同形成原始卵泡。我们已经确定了一个新的，卵母细胞特异性，碱性螺旋-环-螺旋转录因子，FIG（因子在生殖系，α）。单拷贝Fig基因在胚胎干细胞中被破坏，这些细胞已被用于建立小鼠品系。缺乏FIG的雌性小鼠是不育的，因为生殖细胞耗竭继发于围产期不能形成原始卵泡。FIG下游靶点的鉴定应该为卵泡形成的分子基础提供额外的见解。在卵泡发生开始后，FIG还调节编码ZP 1、ZP 2和ZP 3的单拷贝基因的卵母细胞特异性表达（即，在Fig无效小鼠中未检测到转录物）。正常情况下，这三种卵母细胞糖蛋白在卵泡发生期间分泌以形成透明卵母细胞，透明卵母细胞是一种介导订单特异性精子与卵子结合的细胞外基质（例如，人类精子不会与小鼠透明质酸结合）。使用转基因，我们已经确定，小鼠ZP 1是不需要的透明卵母细胞，订单特定的精子结合或生育能力的形成。相比之下，ZP 2和ZP 3都是基质形成所需的，没有基质形成，小鼠是不育的。尽管小鼠ZP 2或小鼠ZP 3被它们的人同源物替换恢复了透明带基质，但它不影响精子结合的特异性（即，小鼠而不是人的精子结合并使封闭在人源化透明带中的卵受精）。正在进行建立表达人ZP 2和ZP 3或小鼠ZP 3蛋白突变形式的小鼠品系的育种研究，以进一步研究精卵相互作用的分子基础。- 卵透明细胞，受精，性别决定，卵母细胞特异性基因表达，生殖系因子

Mouse gestation takes place over 20 days. Germ cells, first detected in mouse embryos at day 7.25, migrate from the extra-embryonic allantois to the genital ridge where the primitive gonad differentiates into an ovary by day 13 in XX females. Using high through-put sequencing and modern informatics to screen urogenital cDNA libraries, we have identified a novel gene located on the X chromosome. This gene, designated Nt2, is expressed preferentially in the somatic cells of female gonads at the time of sex determination. The resultant protein contains a homeobox domain near its carboxyl terminus raising the possibility that NT2 may play a role in gonadogenesis. The gene has been successfully targeted in embryonic stem cells that are currently being used to establish mouse lines for analysis of the null phenotype.At birth the ovary contains its full complement of germ cells, each surrounded by a single layer of granulosa cells which together form the primordial follicles. We have identified a novel, oocyte-specific, basic helix-loop-helix transcription factor, FIG (Factor In the Germline, alpha). The single-copy Fig gene has been disrupted in embryonic stem cells and these cells have been used to establish mouse lines. Female mice lacking FIG are sterile because of germ cell depletion secondary to an inability to form primordial follicles perinatally. Identification of downstream targets of FIG should provide additional insights into the molecular basis of follicle formation. After the onset of folliculogenesis, FIG also modulates the oocyte-specific expression of the single-copy genes that encode ZP1, ZP2 and ZP3 (i.e., zona transcripts are not detected in Fig null mice). Normally, the three zona glycoproteins are secreted during folliculogenesis to form the zona pellucida, an extracellular matrix that mediates order-specific sperm binding to the egg (e.g., human sperm will not bind to the mouse zona pellucida). Using transgenesis, we have determined that mouse ZP1 is not required for formation of the zona pellucida, order-specific sperm binding or fertility. In contrast, both ZP2 and ZP3 are required for matrix formation without which mice are infertile. Although the replacement of either mouse ZP2 or mouse ZP3 with their human homologue restores the zona pellucida matrix, it does not affect the specificity of sperm binding (i.e., mouse, but not human, sperm bind and fertilize eggs enclosed in humanized zonae pellucidae). Breeding studies to establish mouse lines expressing both human ZP2 and ZP3 or mutant forms of the mouse zona proteins are being pursued to further investigate the molecular basis of sperm-egg interactions. - zona pellucida, fertilization, sex determination, oocyte-specific gene expression, factor in the germline,