Ueda Y et al. (2002), Acrosome reaction in sperm of the frog, Xenopus...

XB-ART-7638

Dev Biol 2002 Mar 01;2431:55-64. doi: 10.1006/dbio.2001.0541.

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Acrosome reaction in sperm of the frog, Xenopus laevis: its detection and induction by oviductal pars recta secretion.

Ueda Y , Yoshizaki N , Iwao Y .

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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.

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Species referenced: Xenopus laevis
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	FIG. 1. Confocal fluorescence images of Xenopus sperm stained with LysoSensor Green, showing the sperm with bright fluorescence in a sac-like structure at the top of head (A, B), and the sperm without fluorescence at the top of head (C, D). The images of (A) and (C) were taken from different sperm. (B, C) Higher magnification of (A) and (C), respectively. a, acrosome; n, nucleus; m, middle piece region. Scale bars, 2 m.
	FIG. 2. Electron micrographs of the acrosomal region in Xenopus sperm. (A) A longitudinal section of the acrosomal region, showing an acrosome beneath the plasma membrane. (B, C) Cross sections of the acrosomal region, showing the sperm with the intact acrosomal membranes and the plasma membrane with electron dense materials in the acrosome (B), the sperm with the exposed inner acrosomal membrane (C). pm, plasma membrane; oa, outer acrosomal membrane; ia, inner acrosomal membrane; n, nucleus; nm, nuclear membrane. Scale bars, 1m.
	FIG. 3. Acrosome reaction of LysoSensor-loaded sperm on isolated VE, showing a sperm with acrosome just after binding (A) and disappearance of the acrosome 12 min after binding (B). The sperm was detached from VE and moved slightly after acrosome reaction. (A, B) Taken from the same sperm. The fluorescence in the acrosome seems to be localized at post acrosomal region after acrosome reaction. Left panels, fluorescence images of LysoSensor Green; Right panels, differential interference images of sperm.