Development of cortical vesicles in Sicyonia ingentis ova: Their heterogeneity and role in elaboration of the hatching envelope

Abstract

In the marine shrimp Sicyonia ingentis, ova lack cortical vesicles at spawning. Previous ultrastructural studies suggested that two different populations of cortical vesicles (dense vesicles and the ring vesicles) appear within 30 min post-spawning. These vesicles undergo sequential exocytosis (exocytosis of the dense vesicles followed by exocytosis of the ring vesicles) that leads to the formation of a hatching envelope around the ovum (see Pillai and Clark: Tissue & Cell 20:941-52, 1988). In the present study, lectins were used as molecular probes to study the development of cortical vesicles subsequent to spawning and the role of these vesicles in formation and elaboration of the hatching envelope. Isolated envelopes were screened with 11 different lectins to determine what group(s) were specific to the envelope glycoconjugates; Concanavalin A (Con A), Griffonia simplicifolia (GS II), Lens culinaris (LCA), and wheat germ agglutinin (WGA) bound to the envelopes. FITC-lectin studies of sectioned ova (fixed at various time points after spawning) utilizing WGA and LCA showed different labelling patterns. Data obtained at the light microscopical level indicated that WGA was specific to the dense vesicles and the outer portion of the envelope, while LCA exhibited specificity for the ring vesicles and the inner portion of the envelope. At the ultrastructural level, gold-LCA labelling was seen associated with the cisternal elements (containing ring-shaped structures), ring vesicles, and the inner layer of the fully formed envelope. These data demonstrated that 1) the ring vesicles are formed by fusion of cisternal elements containing ring-shaped structures; 2) the two species of cortical vesicles are chemically heterogeneous; and 3) the components of each type of vesicle contribute to different integral parts (the outer and inner layers) of the hatching envelope.