Intracellular Signal Transduction and Amplification Mechanisms in the Regulation of Oocyte Maturation

Abstract

Meiotic cell division can be induced by various extracellular signals in different organisms. The inducing signals interact with surface receptors. The signal is transduced across the oocyte plasma membrane, into the cytoplasm, where it is amplified by protein phosphorylation. Maturation-promoting factor appears in all meiotic and mitotic cells and is associated with protein phosphorylation. Cells use at least two systems for the activation of protein phosphorylation in response to extracellular stimuli: direct activation of a receptor-associated protein kinase and indirect activation via guanine nucleotide-binding proteins (G-proteins). G-proteins indirectly activate or inhibit protein kinases dependent on cAMP, Ca2+, or diacylglycerol. Oocytes appear to use each of these signals and several different kinases to regulate meiotic cell division. The evidence for the involvement of each of these cellular signal transduction and amplification mechanisms in the regulation of meiotic cell division is discussed. Models are presented to account for possible interactions between various positive and negative modulators.