Ultrustructural Changes Of Early Bovine Oocytes And Oocytes Before And After In Vitro Maturation

The aim of this study was to investigate the ultrastructureal change of bovine oocytes in development. The oocytes on ovaries at different stage and those before and after in vitro maturation were studied by transmission electromicrocopy. The results showed that the oogonium had a big and round nucleus. At early leptonema and late leptonema of elementary oocytes, a dense and linear structure in nucleus and ooplasm, was observed, and the nucleus yawed to one side. In contrast, at diplonema, lampbrush chromosome was found. Few mitochondrias were seen in the cytoplasm of oogonium and these mitochondrias'density was at middle level. At leptonema, the oocytes contained lots of granule and fibrin materials located between mitochondrias. In diplonema oocytes, the mitochondrias were round and had few cristas. In diplonema of elementary oocytes, the mitochondrias were round with few cristas .When the oocytes developed, the amount of mitochondrias became increased, and they were round and the density of plasm was high. In the follicles whose diameter was above 2mm, the mitochondrias formed hood. The distance between oogonium and cumulus oophorus was short. The nucleus of cumulus cells had many figures. There was only a narrow space between elementary oocytes and cumulus oophorus. The distance between antral follicle and cumulus oophorus became big, and the nucleus of cumulus oophorus was round. There were only a few lysosomes in the oogonium; when the oocytes reached early leptonema and leptonema, the number of lysosomes increased. Moreover, the lysosomes clang to mitochondrias. The lysosomes and mitochondrias densely distributed in the cumulus oophorus. In diplonema of elementary oocytes, there were lots of dense lysosomes. These lysosomes formed a large vesicle. In antral follicles, the globular lysosomes turned to linear lysosomes. Few vesicles distributed uniformity in the cytoplasm of the oogonium. The amount of vesicles significantly increased and yawed to one side in the early leptonema and leptonema's oocytes. Many vesicles congregated most of which was besieged by membrane in the diplonema oocytes. There were materials in the vesicles of the antral follicle oocytes, and the vesicles diminished. CGs were not found in the cytoplasm of bovine oogonium. However, there were light CGs in the oolemna of early leptonema and leptonema oocytes. CGs congregated in the diplonema oocytes. In antral follicle oocytes, there were lots of dark CGs, most of which distributed in the oolemna. Some oocytes in the ovary degenerated; Some nucleus of antral follicle oocytes accompanied lipid droplets; Moreover, the halos appeared in the cytoplasm of cumulus oophorus.Zona pellucida (ZP) of oocytes matured in vitro had a tendency to become thicker. But ZP of oocytes with first pobar body was thinner than that of oocytes without first polar body (PB1) after in vitro maturation. Microvilli of oocytes cultured in vitro appeared falling. However, the microvilli of oocytes matured in vitro was thinner and longer, and the microvilli of oocytes without PB1 become shorter and thicker; The oocytes whose nucleus was removed had few microvilli. Lipid droplets'diameter of oocytes cultured in vitro was big. Lipid droplet of ooctyes matured in vitro had two types, moreover these lipid droplets showed up accompanying and become slightly bigger. Lipid droplet of oocytes without PB1 appeared heterogeneous and become markedly bigger. Lipid droplets'density of oocytes without nucleus after maturation appeared dark, and the diameter of these had a descendent tendency. The hooded mitochondrias showed up in three types of oocytes; the proportion of abnormal mitochondrias all descended. The decadency arrangement was largest in oocytes matured in vitro; the amount of mature mitochondrias in oocytes matured in vitro and oocytes after enucleation improved markedly; these mitochondrias in oocytes unmatured in vitro decreased. Oocytes matured in vitro emerged lysosomes-like residual materials. Cytoplasm of oocytes which is deleted after matured in vitro appeared partly solid state. These results show the characteristic of ultrastructural changes during bovine oocyte development, and provide histology and morphologic gist for bovine oocytes development.