Localization of fodrin during fertilization and early development of sea urchins and mice.

Fodrin, a spectrin-like protein, is localized in gametes, zygotes, and embryos from sea urchins and mice. Mammalian fodrin comprises two polypeptides with molecular weights of approximately 240 kDa (alpha) and 235 kDa (beta). An antibody specific for mammalian alpha-fodrin cross-reacted with a 240-kDa polypeptide from sea urchin egg extracts. This indicates that sea urchins contain a protein of similar electrophoretic mobility and immunological properties to mammalian alpha-fodrin. When this antibody was used to stain the sea urchin gametes with indirect immunofluorescence, fodrin-specific fluorescence was localized to the acrosome of the sperm and was distributed over the entire egg near the surface in a punctate pattern similar to the distribution of polymeric actin. During sperm incorporation, the fodrin-specific fluorescence is found at the site of sperm incorporation, in the fertilization cone. After fertilization, the intensity of fodrin fluorescence increases. During mitosis and cytokinesis in sea urchins, the entire surface of the egg remains stained; the cleavage furrow also was stained but no more intensely than was the rest of the egg surface. Antibody labeling with colloidal gold followed by electron microscopy showed that fodrin was loated in the cytoplasm immediately beneath the plasma membrane. In unfertilized mouse oocytes, both actin and fodrin were stained most intensely beneath the membrane adjacent to the meiotic spindle. After insemination, the cell surfaces of the pronucleate egg and the second polar body were stained; however, the actin matrix surrounding the apposed pronuclei did not bind the fodrin antibody. During cytokinesis in the mouse, the cleavage furrow stained more intensely than did the rest of the egg cortex, and in embryos the cell borders were delineated. These results indicate that organisms as unrelated to mammals as sea urchins have fodrin-like proteins; the rearrangements of such proteins suggest that they participate in the actin-mediated events at the cell surface during fertilization and early development in both mice and sea urchins.