Effects of cell cycle dependent kinases inhibitor on nuclear and cytoplasmic maturation of porcine oocytes

The aims of this study were to assess the effectiveness of roscovitine, a p otent inhibitor of cell cyclin kinases, to prevent meiotic resumption in po rcine oocytes, and to test the subsequent fertilisability and developmental competence of these oocytes. Roscovitine blocked porcine oocytes at the GV stage during 22-44 hr of culture. This effect was dose-dependent, and a co ncentration of 25 muM was sufficient to prevent meiotic resumption in 92 +/ - 5% of the oocytes after 22 hr in the presence of EGF and FSH. Cumulus exp ansion was also inhibited under these conditions. The histone H1 kinase act ivity in oocytes was inhibited in a dose-dependent way, and maintained at a basal level with 25 VM of roscovitine. Synthesis of proteins of 29, 47 and 79 kDa, normally synthesized during maturation, was inhibited too. All the se effects were fully reversible. However, the kinetics of maturation were accelerated after roscovitine removal, and the acceleration was more pronou nced after 44 hr of inhibition than after 22 hr. Fertilization of oocytes b locked for 22 hr before a 44 hr maturation was decreased compared to contro l, but was not different from that of oocytes matured for 66 hr. The develo pmental competence was decreased for the oocytes cultured for 66 hr, includ ing or not an inhibition period, but it was less reduced for oocytes mainta ined under inhibition for 22 hr. Roscovitine may thus protect oocytes again st the aging mechanisms responsible for developmental competence loss, but not against loss of fertilisability. In conclusion, roscovitine provides a useful tool to study the morphological and biochemical basis of porcine ooc yte terminal differentiation.