Ultrastructure changes in buffalo (Bubalus bubalis) oocytes before and after maturation in vitro with sericin

The aim of this research was to identify the changes in the cytoplasmic ultrastructure of immature and matured oocytes in buffalo (Bubalus bubalis). Oocytes were matured in vitro in tissue culture medium-199 with and without sericin, and then analyzed by light and transmission electron microscopy. The experiment result showed that the nuclear maturation rate of buffalo oocytes was significantly higher in the presence of sericin (80.6%) than without sericin (68.1%) (P < 0.05). The immature oocytes were characterized by cortical granule clusters in the ooplasm and the absence of perivitelline space (PVS). In contrast, the oocytes matured either with or without sericin showed the formation of PVS, erected microvilli, the migration of cortical granules to the cytoplasmic periphery, and the clear appearance of the mitochondria and vesicle in the oolemma. Interestingly, matured oocytes with sericin have smaller cortical granules than do immature oocytes (P < 0.05). In conclusion, supplementation of 0.05% sericin in the maturation medium can enhance the maturation rate of buffalo oocytes. Several cytoplasmic ultrastructures were relocated and modulated during the in vitro maturation process of buffalo oocytes: PVS development, cortical granules migration to periphery, and mitochondria and vesicles in the cortical region. The ultrastructure was similar between the groups with and without sericin.