Talk:Corona radiata (embryology)

Fair use rationale for Image:Mature Graffian follicle.jpg

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BetacommandBot (talk) 16:59, 2 January 2008 (UTC)

Removal of "it takes the secretions of dozens of sperm to weaken the layer enough for one sperm to penetrate"

I am removing the sentence "It takes the secretions of dozens of sperm to weaken the layer enough for one sperm to penetrate," which was tagged with "citation needed" in March 2013.

This is an outdated model of sperm penetration of the cumulus oophorus that unfortunately still appears to be popularly believed. The most recent scholarly reference I've seen cited proposing this model of sperm penetration is the article by Yanagamachi, R. (1994), "Mammalian fertilization" in The Physiology of Reproduction (E. Knobil and J. D. Neill, eds.), Vol. 1, pp. 189 – 317. Raven Press, New York.

However, from the 2006 edition of the same book:

"...it was proposed [in the 1994 edition article] that the acrosome reaction necessarily occurred while sperm were entering the cumulus matrix, and that the subsequent exocytotic release of acrosomal hyaluronidase locally dispersed that matrix and facilitated sperm passage to the zona pellucida. This model has been reevaluated in light of more recent observations."

Further, from Cardullo, R. A. and Thaler, C. D. (2003), "Function of the egg's extracellular matrix" in Fertilization (D. M. Hardy, ed), pp. 126. Academic Press, San Diego:

Based on in vitro fertilization experiments, researchers proposed that many sperm were needed at the site of the cumulus layer to loosen the matrix and ultimately to allow entry of a single sperm (Yanagamachi, 1994). However, in contrast to the many sperm present during commonly used in vitro fertilization procedures, the situation in vivo is quite different, with the sperm:egg ratio being very small, even approaching ratios of 1:1. In addition, fertilization can be achieved in vitro with small numbers of sperm. These observations suggest that a single sperm cell can penetrate the cumulus layer and to do so it must have a mechanism to overcome the effects of the viscoelastic extracellular matrix.

References