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RESEARCH PRODUCT

Follicle Cells of Styela plicata Eggs (Ascidiacea)

subject

description

Styela plicata eggs are surrounded by large follicle cells that at LM appear as highly vacuolated and columnar in shape; at the apical end of each cell lies a very large and clear vacuole, half of which extends inward. Electron microscope observations show a Single layer of largely spaced box-like follicle cells; the close cell-cell contact at their base is realized by interdigitations. The cell surface shows a peculiar structure, more developed in the latero-basal regions, consisting of a complex of membrane extensions, i.e. microvilli, filopodia and lamellipodia. Filopodia irradiate in all directions towards the adjacent cells and the outermost vitelline coat, thus creating a complex network. The whole of the membrane extensions forms a thin yet compact carpet-like layer, through which the follicle cells are tightly attached to one another and to the vitelline coat. Uncovering of the apical region evidences a large sponge-like granule, probably involved in secretion. At Insemination the majority of spermatozoa is distributed on the apical membrane of the follicle cells; the membrane often breaks after sperm-egg impact.