Sea urchin spectrin in oogenesis and embryogenesis: a multifunctional integrator of membrane-cytoskeletal interactions

Using indirect immunofluorescence microscopy on semithin cryosections of maturing ovarian tissue, eggs, and developing embryos, we have mapped the cellular distribution and dynamic redistribution of spectrin in oogenesis and early embryogenesis. During oogenesis, spectrin is initially found in the cortex of oogonia and previtellogenic oocytes, and later accumulates in the cytoplasm of vitellogenic oocytes on the surfaces of cortical granules, pigment granules/acidic vesicles, and yolk platelets. Following egg activation, spectrin undergoes a rapid redistribution coincident with three major developmental events including: (1) restructuring of the cell surface, (2) translocation of pigment granules/acidic vesicles to the cortex during the first cell cycle, and (3) amplification of the embryo's surface during the rapid cleavage phase of early embryogenesis. The synthesis and storage of spectrin during oogenesis appears to prime the egg with a preestablished pool of membrane-cytoskeletal precursor for use during embryogenesis. Results from this study support the hypothesis that spectrin may function as a key integrator and modulator of multiple membrane-cytoskeletal functions during embryonic growth and cellular differentiation.