Chapter 7 Mechanisms of Activation of Sperm and Egg During Fertilization of Sea Urchin Gametes

Abstract

Publisher Summary This chapter discusses the fertilization of the sea urchin egg. The metabolic and morphological changes of sea urchin gametes during fertilization are the best characterized of all embryos. In organization, this chapter explains the activation of both gametes, first considering the activation of the sperm upon its contact with egg jelly and the resultant cascade of the events leading to sperm–egg attachment and sperm–egg fusion. It then examines the consequences of sperm fusion with the egg that leads: (1) to the responses, excluding other sperm from fusing with the egg and (2) to the responses that result in the activation of embryonic development. The chapter describes the important roles played by intracellular calcium and cytoplasmic pH in turning on the cell metabolism. In sperm plasma membrane, the receptors interact with some component of the egg jelly or egg surface. This leads to increased Ca2+ content, the induction of membrane fusion, and the acrosomal exocytosis. At the same time, there is an acid efflux, polymerization of internal actin, and exposure of sperm lysins and sperm bindins that are attached to the newly formed membrane of the acrosomal process.