ABSTRACT
The extracellular matrix has moved into the limelight as a highly organized structure that is produced by and interacts with cells, often in a highly specific manner. The ultrastructure of the extracellular matrix is being visualized at high resolution by two techniques: the quick-freeze, deep-etch, rotary-shadow method for tissues and isolated cells, and rotary-shadowing of mica-adsorbed macromolecules for visualization of individual purified proteins. The vitelline layer of the sea urchin represents one of the best studied examples of an extracellular matrix. The vitelline layer is secreted by the immature oocyte during its maturation in the ovary, and in the mature egg consists of a thin coating anchored to the cell surface. The vitelline layer on the cell surface is a filamentous layer that is also highly organized. The main sheet consists of a network of anastomozing filaments that are attached to the external surface of the plasma membrane by short posts.
