Interaction of cell cycle kinases, microtubules, and chromatin in ascidianoocytes during meiosis

We used kinase assays and confocal microscopy to study the interaction of c ell cycle proteins with microtubule organising centres (MTOC) and chromatin in ascidian oocytes during meiosis. The activity of maturation promoting f actor (MPF) and mitogen activated protein kinase (MAPK) appear not to be co rrelated in control oocytes. MPF activity peaks during metaphase I and II o f the meiotic cell cycle whereas the activity of MAPK peaks at telophase I and is subsequently degraded to remain at low levels for the remainder of m eiosis. The protein synthesis inhibitor emetine induces the degradation in MPF activity in unfertilized metaphase-I (M-I) oocytes, while MAPK is unaff ected. Emetine does not alter the activities of these cell cycle kinases in fertilized oocytes during meiosis I but MPF activity remains low while MAP K activity is high for an elongated time period and oocytes do not complete meiosis I. Emetine induces maternal MTOC duplication in unfertilized M-I o ocytes and prevents sperm aster growth in fertilized oocytes, but it does n ot alter the M-I meiotic apparatus in unfertilized oocytes. These experimen ts suggest that neither MPF alone nor emetine-sensitive proteins are respon sible for M-I arrest in ascidian oocytes, MAPK may ensure this stability. I n addition, we showed that the maternal MTOC is present at M-l but suppress ed from duplicating in an emetine-sensitive manner. Mel. Reprod. Dev. 56:15 5-162, 2000. (C) 2000 Wiley-Liss, Inc.