Differences in the macromolecular composition of the zona pellucida isolated from pig oocytes, eggs, and zygotes

The macromolecular differences in the zona pellucida (ZP) isolated from pig oocytes, eggs, and zygotes were investigated using two-dimensional polyacrylamide gel electrophoresis. The ZP was isolated from individual cells or zygotes using micropipettes, radiolabeled with 125I and analyzed using disulfide bond reducing and nonreducing conditions. The reduced ZP isolated from oocytes was composed of four glycoprotein components. The gel pattern of the ZP isolated from a single oocyte was indistinguishable from that isolated en masse. The ovulated egg ZP contained the four oocyte components plus three additional macromolecules. Relative to the egg ZP, the zygote ZP lacked one component but had three additional smaller macromolecules. We concluded that: the macromolecular differences between the oocyte and egg ZPs are caused by the addition of macromolecules to the ZP as the egg transits the oviduct, the macromolecular differences between the egg and the zygote ZPs reflect hydrolytic processing of ZP glycoproteins probably by enzymes derived from the egg cortical granules, and the microheterogeneity of the pig ZP glycoproteins is due to posttranslational modification and is not due to population genetic variation.