4 Actin-Membrane Cytoskeletal Dynamics in Early Sea Urchin Development

Abstract

Publisher Summary Eggs and embryos have been used in a vast array of biochemical, biophysical, and cytological studies to ask and answer seminal questions on fertilization, signal transduction, cell cycle regulation, exocytosis, gene expression, cellular induction, and differentiation. Historically, the echinoderm egg and embryo have been particularly fruitful in pushing the envelope of the understanding of complex synergistic interactions among cell signaling events, membrane traffic, and cytoskeletal reorganizations that occur during the course of normal cellular and embryonic differentiation. Nowhere is this better exemplified than in the extraordinary works of Rappaport, Hiramoto, and others who have shown the important relationship that exists between the mitotic spindle and the cortical membrane actin cytoskeleton leading to the induction and formation of the contractile apparatus driving cytokinesis. This chapter focuses on the actin cytoskeleton and its interaction with egg and embryonic membranes during fertilization and morphogenesis. It highlights the known sea urchin egg actin-binding proteins and discusses their structural, functional, and regulatory cytoskeletal-membrane dynamics during development. Fertilization serves as the starting point for reviewing the dynamic interplay between physiological activation and reorganization of the cortical actin-membrane cytoskeleton (filament assembly, cortical granule exocytosis, microvillar elongation, membrane uptake, vesicle sorting) that follows sperm-egg fusion. The chapter provides an appreciation of the sea urchin egdembryo as a cell and developmental model for studying the mechanisms underlying cytoskeletal membrane reorganization and its importance to early embryonic morphogenesis and differentiation.