Association of actin with sperm centrioles: isolation of centriolar complexes and immunofluorescent localization of actin.

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Abstract
The centrioles of cnidarian sperm associate with striated specializations (pericentriolar processes) during spermiogenesis. Three functions were proposed for the role of these structures: an anchoring mechanism for the sperm flagellum; a signal-transmitting mechanism for communication between sperm head and tail; and a contractile mechanism involved in motor function of the sperm flagellum. To investigate these proposed functions, a technique was developed for the isolation and purification of Hydractinia echinala sperm distal centrioles with attached pericentriolar processes. Sodium dodecylsulfate polyacrylamide electrophoretic profiles of whole sperm and pericentriolar process proteins revealed a prominent protein that comigrates with rabbit and penaeid shrimp muscle actin. To label and localize actin in hydroid sperm, a highly specific antiserum to invertebrate actin that cross-reacts with both invertebrate and vertebrate muscle and nonmuscle actin was developed in rabbits. Immunofluorescent double-antibody labeling of hydroid sperm with antiactin demonstrated the presence of actin in the pericentriolar process region of the sperm. It was proposed that pericentriolar process, if contractile, could alter the mid-piece asymmetry of hydroid sperm, facilitating the directional motility that these cells demonstrate in response to egg-released chemoattractants. The present results support this hypothesis.