Ultrastructure of Goat Oocytes Cultured with "Two-step" Protocol

It is hypothesized that if oocyte can be cultured in vitro under condition that maintains meiotic arrest at the germinal vesicle (GV) stage, then they may have the opportunity to acquire greater developmental competence. In this study, goat oocytes were cultured within follicle hemi-sections, which can inhibit GVBD and prolong the duration of GV stage. The changes of ultrastructure of goat oocyte before and after co-culture with follicle hemi-section and after resumption culture were observed. The purpose is to find out the proofs of further capacitation of oocytes, and to observe the feasibility of two-step protocol for oocytes maturation. Before co-culture with follicle hemi-section: perivitelline space have not been formed in the oocyte, neither have the microvilli been released from the zona pellucida, the cortical region have a lot of oraganelles, clusters of cortical granules exit in the cortical region, mitochondrias amass in the cortical region, a number of vacuoles are presented. After co-culture with follicle hemi-section, the results are as follows: perivitelline space is obvious, the microvilli have been released from the zona pellucida and pile up in stacks in the perivitelline space, mitochondria have begun to migrate toward the center of oocyte inclusters, the bulk of the cortical granules are distributed at solitary positions along the oolemma in the part, the number of vacuoles increase obviously, part of cortical region lack organelles. After resumption culture: perivitelline space develops further, the number of microvilli stacks have decreased and become more erect, mitochondria have distributed evenly in the central oolemma, cortical granules are distributed at solitary positions along the oolemma, the number of vacuoles decrease obviously, more parts of cortical region are free of organelles. In contrast to maturation in vitro, inhibition culture by follicle hemi-section contributes more to the formation of perivitelline space, decrease of number and erection of microvilli and the further formation of organelle-free cortex.