Texture of the zona pellucida of the mature pig oocyte. The mammalian egg envelope revisited

Abstract

-The zona pellucida (ZP) of mature pig oocytes is believed to consist of a dense filamentous meshwork, less compact on the inner and outer faces. The uneven surface of the ZP is made of unordered and stretched fibrils surrounding deep funnels which are the openings of the radial canaliculi. The topography of the ZP surface may contribute to the initial interplay between male and female gametes. Using cytochemical techniques for transmission electron microscopy (TEM), such as tannic acid and ruthenium red treatments, we found that the ZP of pig oocytes was essentially made of bundles of fibrils distributed in concentric layers (except in the innermost and outer parts). A correlation appears between the dense structure of the core layer of the ZP and its texture: it is constituted of superposed layers of fibril bundles, whereas only a random meshwork is found in a very thin innermost and in the outer layer. The fascicular configuration may control the permeability of the ZP, giving its semi-rigidity and elasticity, and may facilitate sperm penetration. The liquid crystal-like design of the core layer of the ZP is similar to textures found in the the vitelline envelope (zona radiata) of other vertebrates and possibly of all the deuterostomes. Such texture is probably related to the unique ZP protein composition and to a coordinated synthesis. vitelline envelope / ultrastructural cytochemistry / glycoproteins / liquid crystal-like texture / Sus scrofa Abbreviations PVS: perivitelline space; SEM: scanning electron microscopy; TEM: transmission electron microscopy; ZP: zona pellucida.

New Insights into the Mechanisms of Fertilization: Comparison of the Fertilization Steps, Composition, and Structure of the Zona Pellucida Between Horses and Pigs1

“…A similar texture was previously observed by transmission electron microscopy for pig [83,84] and equine [85,86] ZP. Moreover, the thickness of the equine and porcine ZP in our study was in the range of previous data [85,87].…”

The acrosome of eutherian mammals

“…It is perhaps not always the case (Yanagimachi and Phillips 1984) and not the rule in other species, as discussed by Baltz et al (1988). If the penetration was purely mechanical, it could be explained by the curved trajectory of the slit first observed by Dziuk and Dickmann (1965); the head would be able to negotiate the spongious zona surface and then, step by step, the stratified (liquid crystal) inner texture of the zona (Fléchon et al 2004). Interestingly, zona proteins themselves contain crystalline domains (Monné et al 2008).…”

Mechanical properties of zona pellucida hardening

“…Electron microscopy observation shows that several fibrils are arranged in cylindrical bundles distributed in concentric layers measuring about 250 nm in diameter oriented in strata parallel to the oocyte surface. Bundles, randomly arranged in the inner-and outermost areas, are organized in closely apposed parallel ranks in the core stratified layers (Fle ´chon et al 2004).…”