In vitro biosynthesis of three sulfated glycoproteins of murine zonae pellucidae by oocytes grown in follicle culture.

The zona pellucida is an extracellular glycocalyx that surrounds the growing oocyte and mediates specific biological functions essential to early mammalian development. We have isolated by a novel technique intact zonae pellucidae from a murine follicle culture system which mimics in vivo granulosa cell-oocyte interactions. Using radioactive precursors we have demonstrated that all three zona proteins, ZP-1, ZP-2, and ZP-3, are sulfated glycoproteins. Incubation of the follicle culture with tunicamycin (0.5 microgram/ml), an antibiotic that blocks N-glycosylation, inhibits new protein deposition in the zona. Under these same conditions overall protein synthesis is decreased only 30%. Biosynthetic studies indicate that after 6 days in culture the zona proteins are produced at 0.4 pg/oocyte/h, which represents 2-3% of the total oocyte protein synthesis. This synthesis stops at or before ovulation and the extremely long half-life (greater than 100 h) of the zona may be essential to preserve its known biological functions, all of which occur after ovulation.