Cyclic changes in amphibian egg microvilli occur during the division cycle: implication of MPF.

The microvilli (MV) of Pleurodeles (amphibian) eggs were examined following fertilization and compared with those of artificially activated eggs and enucleated eggs using scanning and transmission electron microscopy. The MV pattern in fertilized eggs was found to undergo a cyclic transformation during the course of the first few division cycles. Similar changes also occurred in the MV of artificially activated eggs and enucleated eggs. The reorganization of the MV was sensitive to cycloheximide and cytochalasin B, but was unaffected by colchicine. Thus, this MV alteration requires protein synthesis and microfilaments but microtubules are not implicated in this process. In addition, the effects on the MV pattern of the maturation or mitosis promoting factor (MPF) were tested. Injection of MPF into eggs at different times during the first division cycle nearly always induced an elongation of the MV. This observation suggests that MPF could regulate either directly or indirectly, via a MPF-sensitive factor, the cyclic transformation of amphibian egg MV.