Intracellular signals trigger ultrastructural events characteristic of meiotic maturation in oocytes of Xenopus laevis

Abstract

Oocytes of Xenopus laevis were treated with agents which induce individual intracellular signals normally evoked during the process of meiotic maturation. Ultrastructural analysis of these oocytes allowed identification of specific second messengers that individually trigger single ultrastructural changes characteristic of the meiotic maturation process: Manipulation of intracellular cAMP levels induced changes in cortical granule position. Cytoplasmic alkalinization triggered a disruption of the annulate lamellae, a specialized organelle in the periphery of oocytes. Activation of protein kinase C caused rapid formation of a cortical endoplasmic reticulum and subsequent disruption of cortical granules. Manipulation of transmembrane calcium flux had varied results dependent upon the agent employed. Two of the treatments, Verapamil and zero external calcium, induced a reorganization in the oocyte periphery. The results indicate that these ultrastructural events are under the control of specific intracellular signals known to be elicited during meiotic maturation.