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. Author manuscript; available in PMC: 2018 Jun 4.
Published in final edited form as: Results Probl Cell Differ. 2017;59:175–200. doi: 10.1007/978-3-319-44820-6_6

Fig. 6.7.

Fig. 6.7

Sequential activation of polyadenylation during oocyte maturation in Xenopus. (a) Outline of the transcriptional and translational status at the key stages of oocyte maturation. (b) Summary of the signaling cascade activated by progesterone during oocyte maturation. Progesterone stimulation releases Ringo mRNA from Pum2-mediated repression. Ringo associates with Cdc-2, phosphorylates CPEB, Cdc-2, and Musashi. Phosphorylated Musashi recruits the PAP Gld2 and activates translation of early class mRNAs. One of them is Mos mRNA. Mos activates the MAPK pathway by phosphorylating MEK. MAPK in turn phosphorylates CPEB at a site distinct from the one phosphorylated by Ringo/cyclin B-Cdc-2. (c) Phosphorylation of CPEB activates translation of masked mRNAs. Translationally inactive (masked) mRNAs are bound by CPEB, ePAB, PARN, Gld-2, and Maskin. Maskin binds to CPEB and eIF4E, blocking association of eIF4E with eIF4G. Polyadenylation–deadenylation cycles by GLD2 and PARN keep the polyA tail short. Phosphorylation of CPEB expels PARN, leading to polyA tail extension. Another factor released from the complex is ePAB, which now binds to the polyA tail and associates with eIF4E by competing out Maskin and recruits eIF4G leading to translation activation