Developmental Genetics of the Mammalian Ovary

哺乳动物卵巢的发育遗传学

• 批准号: 6983611
• 负责人: JURRIEN DEAN
• 金额: --
• 依托单位: NATIONAL INSTITUTE OF DIABETES AND DIGESTIVE AND KIDNEY DISEASES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/6983611
• 关键词: animal genetic material tag; cell differentiation; developmental genetics; egg /ovum; embryogenesis; female; fertilization; gene expression; genetic library; genetically modified animals; germ cells; graafian follicles; human genetic material tag; laboratory mouse; mammalian embryology; molecular cloning; oogenesis; ovary; protein structure; reproductive development; sex differentiation; sperm; transcription factor; zona pellucida glycoproteins

Mammalian female germ cells must successfully complete developmental programs to initiate folliculogenesis that lead to mature gametes capable of fertilization and the transfer of genetic material to the next generation. 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 basic helix-loop-helix transcription factor, FIG-alpha (Factor In the Germline, alpha) and female mice lacking this regulatory factor are sterile because of germ cell depletion secondary to an inability to form primordial follicles. Identification of downstream targets of FIG-alpha should provide additional insights into the molecular basis of follicle formation and other developmental programs important for successful oogenesis. After the onset of folliculogenesis, FIG-alpha also modulates the expression of the single-copy genes that encode ZP1, ZP2 and ZP3. Together they form the zona pellucida surrounding ovulated mouse eggs and two (ZP2 and ZP3), are reported 'sperm receptors'. After fertilization, the zona pellucida is modified ad minimum by cleavage of ZP2 and sperm no longer bind. Cross-taxa sperm binding is limited among mammals and human sperm do not bind to mouse eggs. Using transgenesis to replace mouse ZP2 and/or ZP3 with human homologues, mouse lines with human-mouse chimeric zonae pellucidae have been established. Unexpectedly, human sperm do not bind to huZP2 and huZP2/huZP3 rescue eggs, but mouse sperm bind, in vitro fertilized eggs progress to two-cell embryos, and rescue mice are fertile. Also unanticipated, human ZP2 remains uncleaved after fertilization and mouse sperm continue to bind early rescue embryos. These observations are consistent with a model in which the supramolecular structure of the zona pellucida necessary for sperm binding is modulated by the cleavage status of ZP2. Late in oogenesis, the oocyte becomes transcriptionally inactive and much of the maternal RNA is degraded during meiotic maturation and ovulation. At fertilization, both gametes are transcriptionally inert and the major activation of the embryonic genome occurs at the two-cell stage. The sperm brings little but its genome to fertilization and the activation of early development programs must depend on maternal factors. MATER (Maternal Antigen That Embryos Require) is a cytoplasmic protein that is present in growing oocytes and persists in early embryos. Mice lacking MATER have normal folliculogenesis and ovulate eggs. Although fertilization takes place, embryos do not progress beyond the early cleavage stage. Males are unaffected and MATER represents a maternal effect gene product critical for mammalian development. Investigations are underway to determine its role in transition of the terminally differentiated germ cell into the totipotent stem cells of the early embryo.

哺乳动物雌性生殖细胞必须成功地完成发育程序，以启动卵泡发生，导致能够受精的成熟配子和遗传物质转移到下一代。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基本的螺旋-环-螺旋转录因子，FIG-alpha（Factor In the Germline，alpha），缺乏这种调节因子的雌性小鼠是不育的，因为生殖细胞耗竭继发于无法形成原始卵泡。FIG-alpha的下游靶点的鉴定应该为卵泡形成的分子基础和其他对成功卵子发生重要的发育程序提供额外的见解。在卵泡发生开始后，FIG-alpha还调节编码ZP 1、ZP 2和ZP 3的单拷贝基因的表达。它们共同形成围绕排卵小鼠卵子的透明带，其中两个（ZP 2和ZP 3）被报道为“精子受体”。受精后，透明卵被ZP 2的分裂修饰，精子不再结合。跨分类群精子结合在哺乳动物中是有限的，人类精子不与小鼠卵子结合。使用转基因用人同源物替换小鼠ZP 2和/或ZP 3，已经建立了具有人-小鼠嵌合透明带的小鼠系。出乎意料的是，人类精子不与huZP 2和huZP 2/huZP 3拯救卵结合，但小鼠精子结合，体外受精卵进展为二细胞胚胎，拯救小鼠具有生育能力。同样出乎意料的是，人类ZP 2在受精后仍然未被切割，小鼠精子继续结合早期拯救胚胎。这些观察结果是一致的模型，其中精子结合所需的透明质酸的超分子结构是由ZP 2的分裂状态调制。在卵子发生的后期，卵母细胞在转录上变得不活跃，并且在减数分裂成熟和排卵期间，许多母体RNA被降解。在受精时，两个配子都是转录惰性的，胚胎基因组的主要激活发生在两细胞阶段。精子除了其基因组外，几乎没有给受精带来什么，早期发育程序的激活必须取决于母体因素。MATER（胚胎需要的母体抗原）是一种细胞质蛋白，存在于生长的卵母细胞中，并持续存在于早期胚胎中。缺乏MATER的小鼠具有正常的卵泡发生和排卵卵。虽然受精发生，但胚胎不会超过早期卵裂阶段。雄性不受影响，MATER代表对哺乳动物发育至关重要的母性效应基因产物。研究正在进行中，以确定其在终末分化的生殖细胞向早期胚胎全能干细胞转变中的作用。