Intracytoplasmic sperm injection of frozen-thawed bovine oocytes and subsequent embryo development

Oocyte cryopreservation and intracytoplasmic sperm injection (ICSI) are advantageous to expand their usefulness in genetic engineering. Oocytes matured for 22 hr were vitrified in droplets of cryoprotectants (3.2 M ethylene glycol (EG), 2.36 M dimethyl sulfoxide (DMSO), 0.6 M sucrose) on copper electron microscope (EM) grids. After being warmed, the oocytes were cultured in IVM medium for an additional 2 hr. Sperm treated with dithiothreitol were utilized for ICSI. Oocytes injected with sperm were activated by combination of ionomycin with cycloheximide (CHX). The ICSI oocytes were compared for the rates of pronuclear formation, development, cell number, and the ratio of ICM to those of fresh ICSI and IVF control. The proportion of 2PN formation was significantly higher in IVF control (Group 1) than those in other treated groups. Among the treated groups a significant lower 2PN formation was observed in IVF-frozen-thawed than in ICSI-fresh and frozen-thawed groups. Cleavage rates in IVF-frozen-thawed and ICSI-frozen-thawed groups were significantly lower than those of IVF control and ICSI-fresh groups. In ICSI groups, the rates of cleavage and blastocyst in fresh oocytes were significantly higher than in frozen-thawed. Development rates into blastocysts in the ICSI-fresh and frozen-thawed groups were significantly lower than that of IVF control. Total cell number was significantly lower in both frozen-thawed IVF and ICSI groups than those in IVF-control and ICSI-fresh groups. However, the rates of the remaining cells that were found in the ICM were significantly higher in both frozen-thawed IVF and ICSI than in the IVF-control and ICSI-fresh groups. The results indicated that frozen-thawed bovine oocytes were suitable for ICSI procedure.