Dimeric CPEB undergoes maturation-mediated destabilization in the native condition. (A) To examine the native status of CPEB, clarified lysate from dormant or GVBD oocytes were passed through a size exclusion column. Fractions of eluates were then assessed by Western blotting. Although most of CPEB was in complexes >150 kDa, in the dormant oocyte, there was a population of CPEB fractionating ∼130 kDa, potentially the dimers. In GVBD oocytes (P-CPEB), only a light peak ∼65 kDa, the monomer size, of CPEB could be detected, and the 130-kDa peak was not observed. These data suggest that, in the GVBD cells, CPEB undergoes an alteration such that the free dimeric CPEB is no longer stable. (B) Extracts from stage VI oocytes and GVBD oocytes were assessed by SDS-PAGE with low SDS in the sample buffer. The slow migrating CPEB species ∼130 kDa is evident from stage VI oocytes, but not from GVBD oocytes.
