DEVELOPMENTAL CAPACITY OF BOVINE OOCYTES FOLLOWING INHIBITION OF MEIOTIC RESUMPTION BY CYCLOHEXIMIDE OR 6-DIMETHYLAMINOPURINE

This study was conducted to assess the fertilizability and development al capacity of bovine oocytes which had been maintained in meiotic arr est by either a protein synthesis inhibitor, cycloheximide (CHX), or a n inhibitor of serine/threonine protein kinases, 6-dimethylaminopurine (6-DMAP). Both CHX and 6-DMAP reversibly prevented nuclear maturation of nearly all oocytes for 24 h. After the reversal of arrest, CHX-tre ated oocytes could be successfully matured and fertilized. They develo ped to the blastocyst stage at slightly lower rates than oocytes cultu red without inhibition for 22 h prior to sperm addition but at higher rates than those incubated in a medium containing no inhibitors for 46 h prior to fertilization. Oocytes inhibited by CHX for 48 h matured a nd fertilized normally but failed to develop into blastocysts. Even th ough 6-DMAP-treated oocytes completed meiosis I after removal from the drug, the rates of fertilization and blastocyst formation were lower than for untreated oocytes or CHX-treated oocytes. Effects of adding F SH and/or estradiol-17 beta (E-2) during CHX-inhibition for 24 h were also examined. Embryos from oocytes treated with CHX and E-2 or with C HX and FSH+E-2 developed into blastocysts at similar rates as the cont rols. Further development of inhibited oocytes was examined by transfe rring blastocysts derived from oocytes inhibited by CHX with FSH and E -2 for 24 h to recipient heifers. Two calves were obtained following t ransfer. These results indicate that CHX-inhibited oocytes retain deve lopmental competence, while 6-DMAP-inhibited oocytes after the reversa l of arrest have reduced capacities for fertilization and further deve lopment. The addition of FSH and E-2 during CHX-inhibition improves de velopment to the blastocyst stage of the oocytes that are capable of i nitiating and maintaining pregnancy after embryo transfer to recipient animals. (C) 1997 by Elsevier Science Inc.