ULTRASTRUCTURE OF HUMAN OOCYTES DURING IN VITRO MATURATION / 解剖学报

ABSTRACT

Objective To study the ultrastructure of human oocytes cultured in vitro.Methods Ultrastructure of oocytes at different stages and of different quality were observed under transmission electron microscope(TEM).Immature oocytes at germinal vesicle(GV) stage and at MI stage after germinal vesicle break-down before and after being cultured in vitro,as well as mature oocytes at MⅡ stage after being cultured were evaluated according to their morphology under light microscope,and then studied by TEM. Results At GV stage the microvilli on oocyte surface were rare and shorter.Nucleus with a dense nucleolus was located in the periphery of oocyte.After culture the oocyte microvilli became denser and increased in number.There were rich ooplasm with organelles,such as large numbers of secretion vesicles,mitochondria and lipid droplets in the GV oocyte.The end of cumulus cell expanded and penetrated into the oocyte zone,forming gap junctions with oocyte microvilli.Functional connection of the adjacent cumulus cells was by desmosomes. In mature oocytes the rough endoplasmic reticulum and Golgi apparatus decreased while the smooth endoplasmic reticulum increased in number.Mitochondria degenerated and lipid droplets fused to form bigger ones.Cortical granules were distributed beneath the cytoplasm membrane in a line manner.The cell junctions between oocytes and cumulus cells were interrupted.There were various organelles in the first polar body.The mature oocytes with lower quality appeared to have lots of swollen mitochondria with blurred cristae and membrane.Some of these oocytes had fractured first polar bodies and deformed zona pellucida.Their surrounding cumulus cells showed higher frequency of cell apoptosis.Conclusion The ultrastructure of human oocytes at different stages and of different quality cultured in vitro was revealed.