Mechanism of the reprogramming of gene expression in mammalian oocytes

本研究旨在阐明受精前后卵母细胞基因表达重编程的机制。由于在有丝分裂过程中，分化细胞的基因表达模式是通过“细胞记忆”机制维持的，而卵母细胞中的基因表达模式被重新编程为顶位胚胎中的基因表达模式，因此我们推测，通过初始化程序来消除细胞记忆参与了基因表达的重新编程。我们检测了卵母细胞和胚胎中的组蛋白乙酰化作为细胞记忆的候选标记。免疫细胞化学显示，受精后的植入前胚胎和体细胞在有丝分裂过程中组蛋白的乙酰化保持不变，但在恢复减数分裂后，组蛋白的乙酰化在卵母细胞中消失，这种去乙酰化状态一直维持到中期II(MII)。由于已经证明，当体细胞核转移到MII期卵母细胞时，基因表达模式被重新编程，因此我们检测了这些细胞核中的组蛋白乙酰化。结果表明，移植后所有被检测的赖氨酸残基均被脱乙酰化。这些结果表明，全局组蛋白去乙酰化参与了卵母细胞中基因表达的重新编程。这种减数分裂特异性的组蛋白去乙酰化似乎是由组蛋白去乙酰酶I(HDAC1)与减数分裂染色体结合而诱导的，因为HDAC1在减数分裂过程中与染色体共存，而不是有丝分裂。最后，我们发现在减数分裂过程中，组蛋白去乙酰化受p34^&lt；cdc2&gt；蛋白激酶的调控。

The purpose of this research project is to clarify the mechanism of reprogramming of gene expression in the oocytes before and/or after fertilizaion. Since the gene expression patterns of differentiated cells are maintained by the mechanism of "cell memory" during mitosis and those in the oocytes are reprogrammed into the ones in the totopotent embryos, we postulated that erasing the cell memory is involved in the reprogramming of gene expression by initializing the program.We examined histone acetylations in the oocytes and embryos as a candidate marker of cell memory. Immunocytochemistry with specific antibody against various lysine residues of histories revealed that acetylation of histones was maintained during mitosis in the preimplantaion embryos after fertilization as well as somatic cells but that it disappeared in the oocytes when they resumed meiosis and this deacetylated state was maintained until metaphase II (MII). Since it has been shown that the the gene expression pattern is reprogrammed when the somatic nuclei transferred into MII stage oocytes, we examined histone acetylation in these nuclei. The results showed that all lysine residues examined were deacetylated after transplantation. These results suggested that global histone deacetylation is involved in the reprogramming of gene expression in the oocytes.This meiosis-specific histone deacetylation seemed to be induced by the association of histone deacetylase I (HDAC1) with meiotic chromosomes, since HDAC1 was co-localized with chromosomes during meiosis but not mitosis. Finally, we showed that histone deacetylation is regulated by p34^<cdc2> protein kinase during meiosis.