Fig. 6. Phosphorylation of CPEB in early meiosis correlates with transient, low level MAPK activation, which is independent of Mos synthesis. (A) Oocytes were injected with either Mos sense oligonucleotides (Mos-S) or Mos antisense oligonucleotides (Mos-AS). After 1 hour, progesterone was added and oocytes were collected at times indicated (hr in pg). Protein extracts were analyzed by SDS-PAGE and immunoblotted with anti-P-MAPK and anti-MAPK antibodies. (B) In vitro phosphorylation assay of His-CPEB. Oocytes were cultured in the presence of DMSO or U0126 for 1 hour prior to progesterone addition. Extracts from 90 oocytes selected at the indicated times (hr in pg) were used in His-CPEB phosphorylation assays. CS, Coomassie staining; ³²P, autoradiography.