Studies on the differentiation of egg envelopes. I. The starfish, Astropecten aurantiacus

We have studied the differentiation of the oocyte vitelline coat (VC) and jelly coat (JC) of the starfish, Astropecten aurantiacus. The precursor material of both envelopes is secreted by the oocyte while the follicle cells do not appear to participate in the secretory process. The first indication of differentiation of the VC is the deposition of a fine fibrillar material between the microvilli which emerge from the oocyte surface. External to this, a more loosely organized material becomes the precursor of the JC. At this time both layers are periodic acid-Schiff (PAS)-positive. In a later stage, the material between the microvilli acquires a more compact organization, looses its PAS-positivity while acquiring fucose binding protein (FBP) affinity. On the contrary, the JC remains PAS-positive and FBP-negative. In the full grown oocytes the VC is made up of densely packed fibrils oriented tangentially to the oocyte surface and is tightly bound to the microvilli. The observations are discussed in connection with the problem of the role of the egg envelopes in sperm-egg recognition and in the induction of the acrosome reaction.