Progesterone acts through protein kinase C to remodel the cytoplasm as the amphibian oocyte becomes the fertilization-competent egg.

The fertilization-competent Xenopus egg undergoes a contraction of its cortex towards the apex of the pigmented animal hemisphere within 10 min of fertilization. Evidence suggests that protein kinase C (PKC) is involved in the assembly of this contractile network and we show that PKC is rapidly activated as a result of exposure of oocytes to progesterone. Xenopus oocytes contain at least five different isotypes of PKC. Three actin-binding proteins (i.e. vinculin, talin and ankyrin) appear to play an early role in the assembly of the contractile network and one of the proteins (vinculin) becomes phosphorylated shortly after progesterone treatment as the contractile network is assembling. Our results indicated that progesterone acts through a phospholipase to activate PKC and that PKC participates in the remodeling of the cytoplasmic compartment as the oocyte becomes the egg.