Sea Urchin Egg 100-kDa Dynamin-Related Protein: Identification of and Localization to Intracellular Vesicles

Abstract

We have initiated a study to identify possible tubulin dimer binding proteins from unfertilized sea urchin eggs utilizing tubulin dimer coupled to Sepharose 4B. A 100-kDa polypeptide has been isolated and its interaction with tubulin/microtubules examined. Solution assembly studies indicated the 100-kDa polypeptide potentiated microtubule assembly. The 100-kDa protein also bundled and cosedimented with polymerized microtubules. Rabbit polyclonal anti-egg 100-kDa antibodies cross-reacted with a 100-kDa polypeptide in the eggs of several different sea urchin species and with mammalian brain dynamin, a 100-kDa microtubule binding protein. These biochemical characterizations and immunological results suggest that the sea urchin 100-kDa microtubule binding protein appears to be related to the dynamin protein family. To gain insight into the functional role of sea urchin egg 100-kDa dynamin-related protein, we immunolocalized egg 100-kDa protein in cryosections and isolated cortices of unfertilized eggs. Egg 100-kDa protein was localized to the monolayer of cortical granules that underlie the plasma membrane and to the inner cytoplasm. Immunolocalizations of egg 100-kDa protein in cortices isolated from fertilized eggs detailed the redistribution of the egg 100-kDa onto cortically positioned vesicles. Egg 100-kDa dynamin-related protein was expressed throughout early development with approximately equivalent amounts present in the unfertilized egg and embryo through early gastrulation, followed by an abrupt decrease in the level of expression by the pluteus larval stage.