Effects of sex chromosomes on the developmental potential of the mouse oocyte

性染色体对小鼠卵母细胞发育潜力的影响

• 批准号: RGPIN-2018-04464
• 负责人: TaketoHosotani, Teruko
• 金额: $ 5.25万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=765821
• 关键词: Effects; sex; chromosomes; developmental; potential

My long-term objective is to delineate how sex chromosomes affect the developmental potential of mouse oocytes. In mammalian development, germ cells undergo sexual differentiation according to their gonadal environment, testis or ovary, which is determined by the presence or absence of the Y-linked Sry gene. Therefore, spermatogenesis and oogenesis take place in the presence of XY and XX chromosomes, respectively. The gonadal sex also dictates the phenotypic sex by secretion of sex steroid hormones. When the gonadal sex is reversed, however, the germ cell sex becomes discordant with the chromosomal sex. Both XX males and XY females in humans are infertile, while XY females are fertile in certain rodent species. In Mus musculus, XY females are variably fertile depending on the cause of sex-reversal and genetic background. The B6.YTIR mouse, which develops into an infertile female with an intact Y chromosome, provides an excellent model for studying the effects of sex chromosomes on female fertility. We previously reported that the cause of infertility in the B6.YTIR female is intrinsic to its oocytes; they can reach the Metaphase II (MII) but fail to complete the second meiotic division and rarely develop beyond the zytote-stage after fertilization. This developmental incompetence can be attributed to their defective ooplasm; when XY oocyte nuclei have been transferred into enucleated XX oocytes, the reconstructed oocytes generate healthy offspring. Thus, the Y chromosome in the oocyte makes the ooplasm defective, which leaves the first meiotic division largely intact but disrupts the second meiotic division. In the next 5 years, we will investigate the molecular mechanisms underlying the second meiotic defects in the XY oocyte and investigate the involvement of Y-linked gene(s). (1) To characterize the nature of ooplasmic defects, whether it lies in a deficiency in critical components or the presence of detrimental components, we will transfer a small volume of cytoplasm from an XX oocyte into an XY oocyte or vice versa, followed by maturation in vitro, and examine the second meiotic division after parthenogenic activation (or fertilization). (2) To clarify the molecular mechanism underlying the failure in the second meiotic cytokinesis, we will compare the activity of ARP2/3 pathways, which are essential for maintaining the MII-spindle near the cytokinesis furrow, in XX and XY oocytes before and after activation. (3) To evaluate the role of Y-encoded transcription factor ZFY2 in the ooplasmic defects, we will knock-down its transcripts in the XY oocyte by siRNAs expression in vitro or by shRNAs expression from a transgene in vivo. The results of proposed studies will shed light on the mechanism coordinating the sister-chromatid separation and the second polar body extrusion, and evolution of the Y chromosome associated with the loss of fertility in Mus musculus XY females.

我的长期目标是描述性染色体如何影响小鼠卵母细胞的发育潜力。在哺乳动物发育中，生殖细胞根据其性腺环境、睾丸或卵巢进行性别分化，这是由 Y 连锁 Sry 基因的存在或不存在决定的。因此，精子发生和卵子发生分别在 XY 和 XX 染色体存在的情况下发生。性腺性别还通过分泌性类固醇激素来决定表型性别。然而，当性腺性别逆转时，生殖细胞性别与染色体性别不一致。人类的 XX 雄性和 XY 雌性都是不育的，而 XY 雌性在某些啮齿类动物中是具有生育能力的。在小家鼠中，XY 雌性的生育能力因性逆转的原因和遗传背景而异。 B6.YTIR 小鼠发育成具有完整 Y 染色体的不育雌性，为研究性染色体对雌性生育力的影响提供了一个极好的模型。我们之前报道过 B6.YTIR 雌性不孕的原因是其卵母细胞固有的；它们可以达到中期 II (MII)，但无法完成第二次减数分裂，并且在受精后很少发育超过受精卵阶段。这种发育无能可归因于它们的卵质缺陷。当 XY 卵母细胞核转移到去核 XX 卵母细胞中时，重建的卵母细胞会产生健康的后代。因此，卵母细胞中的 Y 染色体使卵质有缺陷，从而使第一次减数分裂基本完整，但破坏了第二次减数分裂。未来5年，我们将研究XY卵母细胞第二次减数分裂缺陷的分子机制，并研究Y连锁基因的参与。 (1) 为了表征卵质缺陷的性质，无论是关键成分的缺乏还是有害成分的存在，我们将少量细胞质从XX卵母细胞转移到XY卵母细胞中，反之亦然，然后在体外成熟，并检查孤雌激活（或受精）后的第二次减数分裂。 (2) 为了阐明第二次减数分裂胞质分裂失败的分子机制，我们将比较激活前后 XX 和 XY 卵母细胞中 ARP2/3 途径的活性，这些途径对于维持胞质分裂沟附近的 MII 纺锤体至关重要。 (3)为了评估Y编码的转录因子ZFY2在卵质缺陷中的作用，我们将通过体外siRNA表达或通过体内转基因的shRNA表达来敲低其在XY卵母细胞中的转录物。拟议研究的结果将揭示协调姐妹染色单体分离和第二极体挤出的机制，以及与小家鼠 XY 雌性丧失生育能力相关的 Y 染色体的进化。