Ultrastructure of Detergent-Resistant Cytoskeletons in the Noncortical Domain of Sea Urchin Eggs as Revealed by the Quick-Freeze Deep-Etch Technique.

Abstract

ABSTRACT. The ultrastructure of detergent-resistant cytoskeletons in the noncortical cytoplasm of sea urchin eggs was studied by quick-freeze, deep-etch electron microscopy. Twodifferent cytoskeletal organizations were identified in the detergent-treated sea urchin eggs. They were distinguished by the presence or the absence of long actin filaments and probably correspond to the cortex and the noncortical cytoplasm, respectively. The non-cortical cytoplasm was composed of a complex network (designated here as the ground network) of filaments 6 to13 nm in diameter, that interconnected aggregates of small globular materials, yolk granules and a meshwork of uniform filaments (8-9 nm in diameter). The 6 to 13 nm filaments comprising the ground network were branched and associated with filaments of the same or other sizes, resulting in the formation of an extremely complexnetwork. The meshworkof 8-9 nmfilaments was homogeneousin composition and constitutes a novel structure which has not been previously described. The 8-9 nmfilaments were connected to one another at their ends, forming a meshwork of polygons. Meshworks, ranging up to 3 /urn in diameter, were distributed throughout the non-cortical cytoplasm of the egg. Similar cytoplasmic structures were also observed in fertilized eggs.