Czołowska R, Borsuk E
Department of Embryology, University of Warsaw, Warsaw 64, 00-927, Poland.
Dev Biol. 2000 Jul 1;223(1):205-15. doi: 10.1006/dbio.2000.9747.
Growing mouse oocytes are physiologically arrested in the G2 phase of prophase of the first meiotic division. Growing oocytes were isolated from ovaries of 9- to 12-day-old mice and fused with parthenogenetic one-cell eggs or two-cell embryos derived from fertilized eggs. Resulting hybrids were injected with Dig-11-dUTP and examined for DNA replication using immunofluorescence. Parthenogenetic one-cell eggs fused at telophase II, G1, and middle-to-late S phase, and also S-phase two-cell blastomeres, were able to trigger DNA synthesis in oocyte germinal vesicle (GV) in the majority of hybrids cultured to the end of the first cell cycle. Activation of replication in the GV occurred within 2-3 h after fusion of growing oocytes with S-phase eggs. We show indirectly that the reactivation of replication in GVs was not dependent on the breakdown of the GV envelope. Although GVs had the ability to renew DNA replication after fusion, the G2 blastomere nuclei were incapable of reinitiating DNA replication under the influence of S-phase one-cell eggs. We hypothesize that the nuclei of growing oocytes arrested in meiotic prophase are in a physiological state that is equivalent to replication-competent G1, and not G2, nuclei.
生长中的小鼠卵母细胞在第一次减数分裂前期的G2期处于生理停滞状态。从9至12日龄小鼠的卵巢中分离出生长中的卵母细胞，并将其与孤雌生殖的单细胞卵或受精卵来源的二细胞胚胎融合。将所得杂种注射地高辛-11-dUTP，并使用免疫荧光检查DNA复制情况。在大多数培养至第一个细胞周期结束的杂种中，处于减数第二次分裂末期、G1期和S期中期至后期融合的孤雌生殖单细胞卵以及处于S期的二细胞卵裂球，能够触发卵母细胞生发泡（GV）中的DNA合成。生长中的卵母细胞与S期卵融合后2至3小时内，GV中的复制被激活。我们间接表明，GV中复制的重新激活不依赖于GV包膜的破裂。尽管GV在融合后有能力重新进行DNA复制，但G2期卵裂球细胞核在S期单细胞卵的影响下无法重新启动DNA复制。我们推测，停滞在减数分裂前期的生长中卵母细胞核处于一种生理状态，等同于具有复制能力的G1期而非G2期细胞核。
