The egg cortex: from maturation through fertilization.

The peripheral layer of the egg has long been recognized as a region with special properties. Several types of experiments argue for the existence of an egg cortex (reviewed in Wilson, 1925; Chambers and Chambers, 1961; Hiramoto, 1970; Vacquier, 1981). We can cite in chronological order: micromanipulations of the egg with rods and micropipettes; low speed centrifugation experiments that stratify the egg content except for a thin layer of organelles bound to the plasma membrane; the study of the migration in a magnetic field of metal particles injected into the egg and of the elasticity of the egg surface; the isolation of a cell surface complex (or "isolated cortex") comprising the plasma membrane and adhering internal and external macromolecular structures and organelles. All these experiments point to the existence just below the egg membrane of a cortical layer a few microns thick, which is rearranged during maturation, fertilization and development (Vacquier,