Acrosome Reaction in Sperm of the Frog, Xenopus laevis: Its Detection and Induction by Oviductal Pars Recta Secretion

Abstract

Previous electron microscopic observations have shown that the acrosome of the sperm of the frog, Xenopus laevis, comprises a membrane-bounded vesicle covering the anterior-most position of the head. We obtained a sperm suspension from the testes and stained it with LysoSensor Green for observation under a confocal laser scanning microscope and found a bright fluorescence reflecting the presence of the acrosomes at the top of the sperm head in about 64% of the sperm, with no deterioration of their capacity to fertilize. About 40% of the sperm with an acrosome underwent an acrosome reaction in response to Ca(2+) ionophore A23187, as evidenced by a loss of LysoSensor Green stainability, accompanied by breakdown of the acrosomal vesicle. About 53% of the sperm bound to isolated vitelline envelopes underwent an acrosome reaction, whereas both jelly water and solubilized vitelline envelopes weakly induced an acrosome reaction. When the sperm were treated with an oviductal extract obtained from the pars recta, but not the pars convoluta region, about 40% of the sperm with acrosomes underwent an acrosome reaction. The substance containing acrosome reaction-inducing activity in the pars recta extract seemed to be a heat-unstable substance with a molecular weight of greater than 10 kDa. The activity was not inhibited by protease inhibitors but required extracellular Ca(2+) ions. These results indicate that the acrosome reaction occurs on the vitelline envelopes in response to the substance deposited from the pars recta during the passage of the oocytes through the oviduct.

Identification of the sperm motility-initiating substance in the newt, Cynops pyrrhogaster, and its possible relationship with the acrosome reaction during internal fertilization

“…Furthermore, acrosome reaction-inducing activity is localized in the outermost layer of Discoglossus egg-jelly (Campanella et al, 1997), suggesting that a similar mechanism of sperm motility initiation mediated by the acrosome reaction may exist in other amphibian species regardless of their modes of fertilization. On the other hand, this mechanism does not operate in fertilization in X. laevis or B. japonicus, in which the acrosome reaction is induced on the vitelline envelope after their sperm pass through the jelly layer (Yoshizaki and Katagiri, 1982;Ueda et al, 2002). We thus conclude that different mechanisms of sperm motility initiation are required for the success of various modes of fertilization in amphibians.…”

Anuran and pig egg zona pellucida glycoproteins in fertilization and early development

“…We now know that egg jelly glycoproteins and chemical modifications of the envelope are required by sperm to bind and penetrate the VE and to fuse with the egg membrane. Although all the molecules involved in this process, and the molecular and cellular mechanisms of this jelly coat requirement have yet to be completely determined, it seems likely the jelly coat requirement relates to sperm capacitation and/or induction of the acrosome reaction (Ueda et al, 2002;Wolf and Hedrick, 1971;Yurewicz et al, 1975).…”

The egg membrane microdomain-associated uroplakin III-Src system becomes functional during oocyte maturation and is required for bidirectional gamete signaling at fertilization in Xenopus laevis

“…During passage through the oviduct, the extracellular surface of the oocytes is also changed. This includes modification of the coelomic envelope with the pars rectaderived acrosome reaction-inducing substance in Xenopus (ARISX) (Ueda et al, 2002) and a structural transition from coelomic envelope to vitelline envelope (Gerton, 1986). Subsequently, the oocyte outer surface is deposited with multiple jelly layers, by which the oocyte-derived sperm chemoattractant allurin is retained (Olson et al, 2001).…”