An electron microscopic study of sperm penetration into the human egg investments

Abstract

The ultrastructure of human spermatozoa located in the cumulus cells and the zona pellucida of a pro-nuclear egg, and in the zona pellucida of a two-cell egg, both fertilized in-vivo, has been analysed in order to understand how the human spermatozoon penetrates the investing coats of the oocyte. Among the 36 spermatozoa found in the cumulus cells, 31 were phagocytosed by cumulus cells and 5 were wedged in the matrix between the cells. These spermatozoa were acrosome-reacted and their equatorial segment was intact. Six of the seven spermatozoa found in the zona pellucida (four spermatozoa in the pronuclear egg and three in the two-cell egg) had lost the equatorial segment, while the other one was partially reacted. The sperm heads were located in slits with sharp edges. From these findings it was concluded that in the human (1) only few and normal spermatozoa seem to reach the cumulus cells after natural insemination, (2) the acrosome reaction probably occurs sometime before the spermatozoa reach the vicinity of the corona cells, (3) the reaction of the equatorial segment seems to occur during or before the initial phase of zona penetration, since the spermatozoa located in the matrix of the zona pellucida had no equatorial segment. No evidence of the presence of spermatozoa with an intact acrosome in the matrix of cumulus cells or with an intact equatorial segment in the zona pellucida were found.

Acrosome reaction in the cumulus oophorus revisited: involvement of a novel sperm-released factor NYD-SP8

“…Besides, the contents of the acrosome were lost before the sperm penetrated the ZP (Bedford, 1968). Similar to the rabbit, human spermatozoa found in the cumulus cells were all acrosome reacted under electron microscope with no evidence of the presence of spermatozoa with intact acrosome in the cumulus matrix (Pereda and Coppo, 1985). On the contrary, electron microscope studies of spermatozoa recovered from sheep and cow intracervical insemination showed an opposite result.…”

“…To find out where AR is initiated in vivo, various methods have been adopted to observe the morphology and the ultrastructure of acrosome at the head of spermatozoa located in the ampulla of fallopian tube, the cumulus mass and the ZP layer (Pereda and Coppo, 1985;Nakanishi et al, 1999;Hasuwa et al, 2010). In spite of the differences in animal species examined and methodologies adopted, it is consistently found that the spermatozoa in the oviduct are acrosome-intact or occasionally reacted, while the spermatozoa penetrating the zona are acrosome-reacted.…”

Cumulus Oophorus-associated Glycodelin-C Displaces Sperm-bound Glycodelin-A and -F and Stimulates Spermatozoa-Zona Pellucida Binding

“…Therefore, the cumulus oophorus is at an ideal position to modulate the fertilizing ability of the spermatozoa passing through it. Indeed, the cumulus oophorus is known to affect human sperm function (7, 38 -42) and select morphologically normal spermatozoa for fertilization (6,8,43). Cumulus cells also reduce the spermatozoa-zona binding inhibitory activity of human follicular fluid (23).…”

Role of Immune Cells in Pregnancy

“…Clusters of these cells progressively detach, but variable numbers of cells remain around the egg for the first 72 h before the implantation of the blastocyst in the uterus. [33] We have detected both macrophages and CD4þ T cells in all cumuli from women suffering from blocked fallopian tubes, who underwent an in vitro fertilization program. However, only a few NK cells has been occasionally present.…”