Xenopus laevis Egg Jelly Contains Small Proteins That Are Essential to Fertilization

Abstract

The eggs of Xenopus laevis are surrounded by investment layers of egg jelly that interact with the sperm immediately prior to fertilization. Components of these egg jelly layers are necessary for the fertilization of the egg by incoming sperm. Eggs which are stripped of their jelly layers are refractile to fertilization by sperm, but the addition of solubilized jelly promotes fertilization. We have shown previously that the egg jelly layers are composed of a fibrous network of glycoconjugates which loosely hold smaller diffusible components. Extracts of these diffusible components were prepared by incubation of freshly ovulated eggs in high-salt buffers for 12 h at 4 degrees C. This diffusible component extract, when incubated with sperm, promoted the sperm's ability to fertilize dejellied eggs in a dose-dependent manner. In contrast, the high-molecular-weight "structural" glycoconjugates of jelly that remain after extraction of the diffusible components did not increase fertilization efficiency of dejellied eggs nor did nonspecific proteins, carbohydrate polymers, or organic polymers. The diffusible components, analyzed by SDS-PAGE, consisted of a mixture of proteins from 4 to 180 kDa. The protein responsible for fertilization rescue appeared to be <50 kDa and appeared to self-aggregate or to bind to larger proteins. This protein component was required during sperm binding to the egg, its action required an intact egg vitelline envelope, and its action was independent of large soluble polymers such as Ficoll.

Oviduct: roles in fertilization and early embryo development

“…In Xenopus, egg jelly also produces allurin as chemotaxis for sperm attraction (Olson & Chandler 1999, Olson et al 2001. In humans, freshly released cumulus-oocyte complexes (COCs) can secrete progesterone (P 4 ) as a chemoattractant for sperm (Teves et al 2006, Oren-Benaroya et al 2008.…”

Allurin: Exploring the Activity of a Frog Sperm Chemoattractant in Mammals

“…This observation was initially made in Bufo japonicas and Bufo arenaras and more recently in Xenopus laevis (Katagiri 1987 ;Krapf et al 2009 ;Olson and Chandler 1999 ). However, reintroduction of diffusible jelly components (referred to as "egg water") restores the fertilizability of these jellyless eggs almost to their original level of 80 % or greater (Olson and Chandler 1999 ). For this reason, our laboratory tested the possibility that a diffusible jelly component from X. laevis eggs might be acting as a sperm chemoattractant by using two types of assays (Burnett et al 2011a ).…”

Organization of Carbohydrate Components in the Egg-Jelly Layers of the Newt, Cynops pyrrhogaster

“…Egg-jelly of amphibians contains some diffusible components, which is an important feature for fertilization (Ishihara et al, 1984;Al-Anzi and Chandler, 1998;Ukita et al, 1999;Olson and Chandler, 1999;Onitake et al, 2000). Newts undergo internal fertilization (Elinson, 1986), and sperm are directly inseminated onto the surface of egg-jelly at the exit of the oviduct.…”

“…Egg-jelly also sustains cations that support the induction of the sperm-egg interaction (Bufo japonicus: Ishihara et al, 1984). Recently, it was reported that a fertilization promotion factor exists in Xenopus (Olson and Chandler, 1999). These factors act at the correct time and place in or around egg-jelly, thereby leading to successful fertilization.…”