Starfish oocyte maturation: from prophase to metaphase

The biochemical pathways underlying the prophase/metaphase transition have been studied extensively in isolated starfish oocytes. These cells are released from their meiotic prophase arrest by 1-methyladenine. This hormone interacts with plasma membrane receptors coupled to heterotrimeric G-proteins. Early events following 1-methyladenine/receptor interaction include a decrease of cAMP concentration and possibly involve tyrosine kinases, phospholipases A2 and C, proteases and phosphatase 2A. Later events include the activation of an M phase-Promoting Factor (MPF) through dephosphorylation/phosphorylation of its p34^cdc2 and cyclin B subunits, MPF translocation to the nucleus and activation of the MAP-kinase p44^mpk. Starfish oocytes provide an exceptional model to investigate a hormone-regulated cell cycle phase as well as a unique source for the purification of cell cycle control elements.