Tan Jing-He, Wang Hui-Li, Sun Xing-Shen, Liu Yong, Sui Hong-Shu, Zhang Jie
Laboratory for Animal Reproduction and Embryology, College of Animal Science and Veterinary Medicine, Shandong Agricultural University, Tai-an City, Shandong Province 271018, Peolple's Republic of China.
Mol Hum Reprod. 2009 Jan;15(1):1-9. doi: 10.1093/molehr/gan069. Epub 2008 Nov 18.
In all the studied mammalian species, chromatin in the germinal vesicle (GV) is initially decondensed with the nucleolus not surrounded by heterochromatin (the NSN configuration). During oocyte growth, the GV chromatin condenses into perinucleolar rings (the SN configuration) or other corresponding configurations with or without the perinucleolar rings, depending on species. During oocyte maturation, the GV chromatin is synchronized in a less condensed state before germinal vesicle breakdown (GVBD) in species that has been minutely studied. Oocytes may also take on a SN/corresponding configuration during early atresia, but they undergo GVBD at the advanced stage of atresia. As not all the species show the SN configuration while in all the species, gene transcription always stops at the late stage of oocyte growth, it is suggested that not the formation of perinucleolar rings but a thorough condensation of GV chromatin is essential for transcriptional repression. The GV chromatin configuration is highly correlated with oocyte competence; oocytes must end the NSN configuration before they gain the full meiotic competence, and they must take on the SN/corresponding configurations and stop gene transcription before they acquire the competence for early embryonic development. While factors inhibiting follicle atresia tend to synchronize oocytes in a chromatin configuration toward maturation, factors inducing follicle atresia tend to synchronize oocytes in a chromatin configuration reminiscent of early atresia. Furthermore, although condensation of GV chromatin is associated with transcriptional repression, both processes may not be associated with histone deacetylation during oocyte growth.
在所有研究的哺乳动物物种中，生发泡（GV）中的染色质最初是解聚的，核仁不被异染色质包围（NSN构型）。在卵母细胞生长过程中，GV染色质凝聚成核仁周围环（SN构型）或其他有或没有核仁周围环的相应构型，这取决于物种。在卵母细胞成熟过程中，在经过详细研究的物种中，GV染色质在生发泡破裂（GVBD）之前会同步到一种凝聚程度较低的状态。卵母细胞在早期闭锁时也可能呈现SN/相应构型，但它们在闭锁的晚期会经历GVBD。由于并非所有物种都呈现SN构型，而在所有物种中，基因转录总是在卵母细胞生长后期停止，因此有人提出，对于转录抑制而言，关键不是核仁周围环的形成，而是GV染色质的彻底凝聚。GV染色质构型与卵母细胞的能力高度相关；卵母细胞在获得完全减数分裂能力之前必须结束NSN构型，并且在获得早期胚胎发育能力之前必须呈现SN/相应构型并停止基因转录。虽然抑制卵泡闭锁的因素倾向于使卵母细胞在染色质构型上同步向成熟发展，但诱导卵泡闭锁的因素倾向于使卵母细胞在染色质构型上同步到类似于早期闭锁的状态。此外，虽然GV染色质的凝聚与转录抑制有关，但在卵母细胞生长过程中，这两个过程可能都与组蛋白去乙酰化无关。
