Abstract
Hamster cumulus-oocyte complexes (COCs) were recovered by dissection of antral follicles of ovaries for the germinal vesicle (GV) or metaphase I (MI) stages, and by flushing the oviduct for the metaphase II (MII) stage. The surface morphological characteristics of the oocyte and its investments at each time point were evaluated by scanning electron microscopy (SEM). Oocyte diameter was also measured during the SEM analysis. The cumulus cells had a compact structure with minimal intercellular spaces among them in the GV-stage oocytes. They became greatly expanded with increased intercellular spaces at the MI and MII stages. The zona pellucida (ZP) had an open mesh-like structure, and the size and number of mesh holes increased at the MII stage. The vitelline surface of oocytes at the GV stage was characterized by relatively sparse distribution of microvilli (MV). After maturation, the MV increased in density. The diameter of oocytes decreased significantly during maturation from 82 to 77 μm (P<0.01). Thus the hamster oocyte maturation processes were found to involve the expansion of cumulus cells, an increase in the mesh holes of the ZP and development of MV on the vitelline membrane.
