INDUCTION OF ASTER FORMATION AND CLEAVAGE IN EGGS OF THE SEA URCHIN HEMICENTROTUS PULCHERRIMUS BY INJECTION OF SPERM COMPONENTS*

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Abstract
Studies were made on which components of sperm were able to induce aster formation and cleavage of eggs of the sea urchin H. pulcherrimus. The sperm components were separated by homogenization and centrifugation into the following 3 fractions: the head-midpiece, midpiece and tail. The head-midpiece fraction was then divided into 2 subfractions, the centriole subfraction and the centriole-free subfractions. Each fraction was injected into unfertilized eggs, and after 15-30 min the eggs were inseminated. The ability of a fraction or a subfraction to induce aster formation and cleavage was deduced from the frequency of multipolar cleavage. The head-midpiece fraction and the centriole subfraction were effective in inducing aster formation and cleavage, but the other fractions were not. Isolated centrioles from sea urchin sperm may act as division centers in the egg.