Ducibella T, Kurasawa S, Rangarajan S, Kopf G S, Schultz R M
Department of Obstetrics and Gynecology, New England Medical Center, Boston, Massachusetts 02111.
Dev Biol. 1990 Jan;137(1):46-55. doi: 10.1016/0012-1606(90)90006-5.
Fertilization results in cortical granule exocytosis, which is thought to be involved in modifications of the zona pellucida that constitute the zona pellucida block to polyspermy. A previous report demonstrated that a decrease in the number of Lens culinaris agglutinin-staining granules, which are likely to be cortical granules, occurred during in vivo mouse oocyte maturation with arrest at metaphase II, as well as the formation of a cortical granule-free domain in the area of the metaphase II spindle (T. Ducibella, E. Anderson, D.F. Albertini, J. Aalberg, and S. Rangarajan, 1988, Dev. Biol. 130, 184-197). We extend these observations by reporting here that germinal vesicle-intact oocytes matured in vitro to metaphase II in either the absence or the presence of serum develop a cortical granule-free domain and have reduced numbers of cortical granules when compared to germinal vesicle-intact oocytes; these changes are similar to those of oocytes matured in vivo. The reduction in the number of cortical granules requires germinal vesicle breakdown, since it is prevented by dibutyryl cAMP, which inhibits germinal vesicle breakdown in vitro. The ability of oocytes to respond to the calcium ionophore A23187 with a reduction in the number of cortical granules is also associated with meiotic maturation and develops between 7 and 12 hr after initiation of maturation. The maturation-associated reduction in the number of cortical granules is likely to represent cortical granule exocytosis, since this reduction is accompanied by the formation of a cortical granule-free domain and a conversion of ZP2 to ZP2f when the oocytes are matured in vitro in serum-free medium; this zona pellucida modification occurs following fertilization and is thought to be due to cortical granule exocytosis. In contrast, the loss of cortical granules and development of the cortical granule-free domain of oocytes matured in vitro in the presence of serum is not accompanied by the modification of ZP2. The inhibitory effect of serum on the ZP2 modification may afford in vivo a physiological mechanism to prevent a precocious modification of the zona pellucida that could result in a premature block to polyspermy and hence inhibit fertilization.
受精导致皮质颗粒胞吐，这被认为与透明带的修饰有关，这些修饰构成了对多精受精的透明带阻断。先前的一份报告表明，在体内小鼠卵母细胞成熟并停滞于中期II的过程中，可能是皮质颗粒的菜豆凝集素染色颗粒数量减少，同时在中期II纺锤体区域形成了一个无皮质颗粒区（T. 杜西贝拉、E. 安德森、D.F. 阿尔贝蒂尼、J. 阿尔伯格和S. 兰加拉扬，1988年，《发育生物学》130卷，184 - 197页）。我们在此扩展这些观察结果，报告如下：与生发泡完整的卵母细胞相比，无论有无血清，在体外成熟至中期II的生发泡完整卵母细胞都会形成一个无皮质颗粒区，且皮质颗粒数量减少；这些变化与体内成熟的卵母细胞相似。皮质颗粒数量的减少需要生发泡破裂，因为二丁酰环磷腺苷（dibutyryl cAMP）可阻止其减少，二丁酰环磷腺苷在体外可抑制生发泡破裂。卵母细胞对钙离子载体A23187作出反应导致皮质颗粒数量减少的能力也与减数分裂成熟相关，且在成熟开始后7至12小时之间出现。与成熟相关的皮质颗粒数量减少可能代表皮质颗粒胞吐，因为当卵母细胞在无血清培养基中体外成熟时，这种减少伴随着无皮质颗粒区的形成以及ZP2向ZP2f的转化；这种透明带修饰在受精后发生，被认为是由于皮质颗粒胞吐所致。相比之下，在有血清存在的情况下体外成熟的卵母细胞皮质颗粒的丢失和无皮质颗粒区的形成并未伴随着ZP2的修饰。血清对ZP2修饰的抑制作用可能在体内提供了一种生理机制，以防止透明带过早修饰，这种过早修饰可能导致对多精受精的过早阻断，从而抑制受精。
