Amleh A, Smith L, Chen H, Taketo T
Urology Research Laboratory, Department of Surgery, McGill University, Montreal, Quebec, H3A 1A1, Canada.
Dev Biol. 2000 Mar 15;219(2):277-86. doi: 10.1006/dbio.1999.9600.
In the mammalian gonadal primordium, activation of the Sry gene on the Y chromosome initiates a cascade of genetic events leading to testicular organization whereas its absence results in ovarian differentiation. An exception occurs when the Y chromosome of Mus musculus domesticus from Tirano, Italy (Y(TIR)), is placed on the C57BL/6J (B6) genetic background. The B6.Y(TIR) progeny develop only ovaries or ovotestes despite Sry transcription in fetal life. Consequently, the XY offspring with bilateral ovaries develop into apparently normal females, but their eggs fail to develop after fertilization. Our previous studies have shown that the primary cause of infertility can be attributed to oocytes rather than their surrounding somatic cells in the XY ovary. This study attempted to identify the defects in oocytes from the B6.Y(TIR) female mouse. We examined the developmental potential of embryos from XY and XX females after exchanging their nuclear components by microsurgery following in vitro maturation and fertilization. The results suggest that both nuclear and cytoplasmic components are defective in oocytes from XY females. In the XY fetal ovary, most germ cells entered meiosis and their autosomes appeared to synapse normally while the X and Y chromosomes remained unpaired during meiotic prophase. This lack of X-Y pairing probably caused aneuploidy in some secondary oocytes following in vitro maturation. However, normal numbers of chromosomes in the rest of the secondary oocytes indicate that aneuploidy alone can not explain the nuclear defect in oocytes.
在哺乳动物性腺原基中，Y染色体上Sry基因的激活引发一系列遗传事件，导致睾丸组织形成；而缺乏该基因则会导致卵巢分化。有一种例外情况，即来自意大利蒂拉诺的小家鼠（Mus musculus domesticus）的Y染色体（Y(TIR)）置于C57BL/6J（B6）遗传背景下时。尽管在胎儿期有Sry转录，但B6.Y(TIR)后代仅发育出卵巢或卵睾。因此，具有双侧卵巢的XY后代发育成明显正常的雌性，但它们的卵子在受精后无法发育。我们之前的研究表明，不育的主要原因可归因于XY卵巢中的卵母细胞而非其周围的体细胞。本研究试图确定B6.Y(TIR)雌性小鼠卵母细胞中的缺陷。我们在体外成熟和受精后，通过显微手术交换XY和XX雌性胚胎的核成分，检查了胚胎的发育潜力。结果表明，XY雌性的卵母细胞中核成分和细胞质成分均有缺陷。在XY胎儿卵巢中，大多数生殖细胞进入减数分裂，其常染色体似乎正常配对，而在减数分裂前期，X和Y染色体仍未配对。这种X-Y配对的缺乏可能导致体外成熟后一些次级卵母细胞出现非整倍体。然而，其余次级卵母细胞中正常数量的染色体表明，仅非整倍体不能解释卵母细胞中的核缺陷。
