Synthesis of fucosyl-containing glycoproteins of the vitelline coat in oocytes of Ciona intestinalis (Ascidia).

The sperm receptors of the ascidian oocyte are located at the outer surface of the vitelline coat (formerly called the chorion). The fucose residues are the receptor's most important components for sperm recognition and binding. We asked whether the fucosyl-containing glycoproteins of the vitelline coat are a product of the oocyte, the follicle cells, or the test cells. Ovaries of Ciona intestinalis were injected with L-[3H]fucose and the progress of its incorporation was followed by using autoradiography and sodium dodecyl sulfate/polyacrylamide gel electrophoresis of the injected gonads and of the isolated vitelline coats. We found that incorporation of fucose begins within the vitellogenic oocytes, and fucose slowly accumulates in the differentiating vitelline coat. At no time could fucose incorporation be detected in the follicle cells or in the test cells. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis of vitelline coats prepared from the injected ovaries showed fucose incorporation into the same three glycoproteins present in vitelline coats from mature oocytes and identified by their affinity for 125I-labeled fucose-binding protein [Pinto, M. R., De Santis, R., D'Alessio, G. & Rosati, F. (1981) Exp. Cell Res. 132, 289-295]. A radioactive band not found in the mature oocyte was also present.