Eppig J J, Schultz R M, O'Brien M, Chesnel F
Jackson Laboratory, Bar Harbor, Maine 04609.
Dev Biol. 1994 Jul;164(1):1-9. doi: 10.1006/dbio.1994.1175.
This paper focuses on the relationship between the developmental programs that regulate nuclear and cytoplasmic maturation of mouse oocytes. As oocytes near completion of their growth phase, they become competent to resume meiosis when isolated from the small antral follicles and cultured, but the progression of meiosis in many of these oocytes stops at metaphase I (MI). With further growth and development at the germinal vesicle (GV) stage, however, these oocytes become competent to complete nuclear maturation and progress to metaphase II (MII). In this study, about 44% of the oocytes were arrested at MI after isolation from the small antral follicles of 18-day-old mice and culture for 16 to 17 hr. Upon insemination, these MI-arrested oocytes produced the first polar body, formed pronuclei, cleaved, and developed to the blastocyst stage. Seventy five percent of these blastocysts were triploid, the remainder were diploid. Treatment of MI-arrested oocytes with calcium ionophore resulted in the completion of the first meiotic division and parthenogenetic activation. Moreover, while the pattern of proteins synthesized in MI-arrested oocytes was quite different from that of normal MI oocytes as determined by [35S]methionine labeling and two-dimensional gel electrophoresis, it was similar to that of MII-arrested oocytes. It was therefore concluded that some critical aspects of cytoplasmic maturation can occur in oocytes whose nuclear maturation is arrested at MI. In addition, triggers that promote entry of MII-arrested oocytes into anaphase II are sufficient to drive MI-arrested oocytes into anaphase I and to produce the first polar body when the triggers are generated in mature cytoplasm. The developmental capacity of MII oocytes that matured in vitro after isolation from 18- or 26-day-old mice were compared. The frequency of fertilization and cleavage to the 2-cell stage was equal in both groups. In surprising contrast, the ability to complete the 2-cell stage to blastocyst transition occurred much more frequently when the oocytes were from the 26- than the 18-day-old mice (82 and 27%, respectively). Thus, even though both groups of oocytes had completed nuclear maturation by progressing to MII, oocytes from the smaller follicles of the younger mice were deficient in maternal factors essential for development of embryos beyond the 2-cell stage. Further differentiation of these GV-stage oocytes of small antral follicles is therefore required to produce eggs competent of completing preimplantation development.
本文聚焦于调控小鼠卵母细胞核成熟与细胞质成熟的发育程序之间的关系。当卵母细胞接近其生长阶段尾声时，从小腔卵泡中分离并培养后，它们具备了恢复减数分裂的能力，但许多此类卵母细胞的减数分裂进程会在中期I（MI）停止。然而，在生发泡（GV）期随着进一步生长发育，这些卵母细胞能够完成核成熟并进入中期II（MII）。在本研究中，从18日龄小鼠的小腔卵泡中分离并培养16至17小时后，约44%的卵母细胞停滞在MI期。授精后，这些停滞在MI期的卵母细胞排出第一极体，形成原核，进行卵裂，并发育至囊胚期。这些囊胚中有75%是三倍体，其余为二倍体。用钙离子载体处理停滞在MI期的卵母细胞可导致第一次减数分裂完成及孤雌激活。此外，通过[35S]甲硫氨酸标记和双向凝胶电泳确定，停滞在MI期的卵母细胞中合成的蛋白质模式与正常MI期卵母细胞的模式有很大不同，但与停滞在MII期的卵母细胞的模式相似。因此得出结论，在核成熟停滞在MI期的卵母细胞中，细胞质成熟的一些关键方面可以发生。此外，当在成熟细胞质中产生促使停滞在MII期的卵母细胞进入后期II的触发因素时，这些触发因素足以驱动停滞在MI期的卵母细胞进入后期I并排出第一极体。比较了从18日龄或26日龄小鼠分离后体外成熟的MII期卵母细胞的发育能力。两组中受精和卵裂至2细胞期的频率相同。令人惊讶的是，与18日龄小鼠相比，当卵母细胞来自26日龄小鼠时，完成从2细胞期到囊胚期转变的能力出现得更为频繁（分别为82%和27%）。因此，即使两组卵母细胞都通过进入MII期完成了核成熟，但来自较年幼小鼠较小卵泡的卵母细胞缺乏胚胎发育至2细胞期之后所必需的母体因子。因此，需要对这些小腔卵泡的GV期卵母细胞进行进一步分化，以产生能够完成植入前发育的卵子。
