Prevention of zona hardening in non-human primate oocytes cultured in protein-free medium

BACKGROUND: Development of a protein-free medium for in vitro maturation of oocytes that prevents zona hardening is essential for the study of components that affect the maturation process. METHODS: Immature macaque oocytes were cultured in modified CMRL medium with serum protein or without protein with or without polyvinyl alcohol (PVA)] for 24 hours. RESULTS: Sperm penetration of oocytes cultured for 24 hours prior to insemination was poor in CMRL medium alone, but was dramatically improved in CMRL medium with the addition of either PVA or BCS. In the second experiment, in vivo matured oocytes were cultured in CMRL with PVA or serum for 6 hours prior to insemination. The incidence of fertilization and embryo development to the blastocyst stage were similar in CMRL with PVA. CONCLUSIONS: These results indicate that fertilization failure occurs when macaque oocytes are cultured in medium without protein, but can be prevented with PVA.