Perivitelline space of mammalian oocytes: Extracellular matrix of unfertilized oocytes and formation of a cortical granule envelope following fertilization

Abstract

Extracellular matrices (ECM) present around unfertilized and fertilized mammalian oocytes were studied ultrastructurally in samples prepared in the presence of ruthenium red to facilitate stabilization of extracellular materials. Unfertilized mouse, hamster, and human oocytes have an ECM comprising granules and filaments in their perivitelline spaces (PVS). This matrix is more abundant in the human than in hamsters and mice. The granule/filament matrix appears identical to the matrix seen between cumulus and corona radiata cells following ruthenium red processing and previously shown to comprise protein and hyaluronic acid. By including ruthenium red during fixation, it is possible to demonstrate the existence of cortical granule exudate in the PVS of fertilized oocytes from hamsters, mice, and humans. Much of the cortical granule exudate is trapped in the PVS and forms a new coat around the fertilized oocyte. This material is particulate when stained with ruthenium red and appears to be uniformly dispersed around the entire oocyte surface. We refer to this new coat as the cortical granule envelope. This envelope is observed in the PVS of all developmental stages up to and including blastocysts in all three species. Following hatching of mouse and hamster blastocysts, the cortical granule envelope is no longer present. Possible functions of this envelope are discussed.

Mammalian cortical granules: Contents, fate, and function

“…The CGE disperses to fill the PVS and is made up of many small electron-dense granules. The CGE is present throughout preimplantation embryonic development in the hamster and mouse, but is not observed around hatched blastocysts (Dandekar and Talbot, 1992).…”

“…such as glycoconjugates (Luft, 1971) and can be used to stabilize extracellular matrices for ultrastructural examination by including it in the primary fixative (Gordon et al, 1975;Dandekar and Talbot, 1992). RR staining cannot be used to localize directly glycosylated material to CG in unfertilized oocytes because the dye is not able to penetrate through plasma membranes.…”

“…A new coat can be seen within the PVS of in vivo fertilized hamster, mouse, and opossum oocytes, and in vitro fertilized human oocytes when they are fixed in the presence of RR (Dandekar and Talbot, 1992;Dandekar et al, 1993). This coat was named the cortical granule envelope (CGE) because it seems to be comprised of the same material seen in freshly exocytosed CG.…”

Insights into the molecular basis of sperm–egg recognition in mammals

“…Earlier investigators in mouse and other vertebrates have implicated cortical granule exocytosis in the block to zona penetration. The cortical granule contents presumably diffuse into the zona pellucida and prevent sperm penetration either by enzymatically or mechanically modifying the zona matrix (Dandekar & Talbot 1992, Quill & Hedrick 1996, Green 1997. The mechanism by which this occurs in mice remains to be determined.…”

Cell volume regulation in mammalian oocytes and preimplantation embryos

“…By the time they develop into mature MII eggs, oocytes have developed a perivitelline space (PVS) between the oocyte plasma membrane and zona pellucida (Dandekar and Talbot, 1992;Talbot and Dandekar, 2003). Although the development of the PVS had been largely assumed to be the result of the loss of oocyte volume to the first polar body, the PVS actually develops well before the extrusion of the first polar body and also develops in oocytes maintained in GV arrest that do not form a polar body (Inoue et al, 2007).…”