Dimerization of CPEB facilitates GVBD-regulated protein destruction. (A) WT, dimeric form, or monomeric form of CPEB were expressed in dormant oocytes, which were then induced into GVBD by progesterone. Quantification from up to five independent experiments is shown in the lower panel. Compared with endogenous and WT CPEB, which were down-regulated after GVBD, the monomeric form of CPEBs, i.e., ΔRRM, CPEB-RRM2, and 6A, were stable along the time course. (B) HA-tagged CPEB and FLAG-tagged cdk1, plx1, and β-TrCP were co-expressed in oocytes, followed by IP with HA antibodies and Western blotting. Monomeric CPEBs were deficient of binding to destruction-related factors, including E3 ligase β-TrCP and its upstream kinase plx1, which explains the deficiency of the regulated destruction. In addition, the dimeric CPEBs bound to polyadenylation factors, symplekin, CPSF100, and ePAB, more efficiently. A triangle to the left of the HA(CPEB) blot indicates nonspecific reactivity of HA antibodies. Actin served as a negative control for IP.
