Sperm-egg interaction in penaeoidean shrimps. In：I C. Liao and J. Baker (eds.)

Abstract

The sperm of penaeoidean shrimps are nonmotile cells consisting of (1) a main body containing an uncondensed nucleus, (2) a cap region containing acrosomal and subacrosomal elements, and (3) an anterior appendage which is continuous with the acrosomal vesicle. At spawning, mated female release both sperm and eggs. The sperm binds, via the tip of their anterior appendage, to the egg's vitelline envelope and repidly undergoes acrosomal exocytosis. Once a sperm has undergone exocytosis, it penetrates the egg's vitelline envelope. The sperm, which has successfully penetrated the vitelline envelope, becomes closely associated with the egg's oolemma and resides on the egg oolemma surface for some time prior to fusion with the egg. In the Sicyonia, the main body of the fertilizing sperm undergoes swelling coin-cident with acrosomal filament formation, whereas in other penaeiodean shrimps, the sperm undergoes acrosomal exocytosis only prior to fusion with the egg's oolemma. Newly spawned eggs of penaeiodean shrimps are isolecithal and in metaphase 1 arrest. The egg is surrounded by a thin vitelline envelope and jelly precursors are stored in ectracellular crypts formed by invaginations of the oolemma underneath the vitelline envelope. Following spawning into seawater into seawater, the egg undergoes a series of activation changes including: (1) release of jelly precursors from cortical crypts, (2) elevation and loss of the vitelline envelope, (3) transition of the released jelly precursors into a homogeneous jelly layer that forms around the egg, (4) resumption and completion of meiotic maturation, and extrusion of the first and the second polar bodies, and (5) a massive cortical vesicle exocytosis that leads to the formation of an extracellular hatching envelope. These activation events are triggered by exposure to seawater and do not require fertilization. Fertilized and unfertilized eggs undergo the same sequence of events; however, sperm-egg interaction is critical for normal cell cleavage and embryonic development. In this paper, the events of sperm and egg activation during sperm-egg interaction of some penaeiodean shrimps are compared and discussed.