Receptor for activated C kinase (RACK) and protein kinase C (PKC) in egg activation

In somatic cells, translocation of PKCs is facilitated by receptor for activated C kinase (RACK); however its involvement in egg activation is still elusive. We have followed the translocation pattern of conventional and novel PKCs (cPKCs and nPKCs, respectively) upon egg activation. Confocal microscopy indicated the expression and localization of RACK1, a specific receptor protein for cPKCs. Activation of MII eggs, led to translocation to the egg cortex of PKCα, βII and δ and the co-translocation of RACK1, with both PKCα and PKCβII. The association of PKC and actin, both known to be involved in cortical granules exocytosis (CGE) with RACK1, was demonstrated by co-immunoprecipitation. Egg activation resulted in an increased RACK1 level along with a decreased level of PKCβII. Based on these results, we suggest that upon egg activation, RACK1 shuttles activated cPKCs to the egg cortex, thus facilitating CGE.