Zhao Longmei, Reim Kerstin, Miller David J
Department of Animal Sciences, University of Illinois, 1207 West Gregory Drive, Urbana, Illinois 61801, USA.
Reproduction. 2008 Sep;136(3):323-34. doi: 10.1530/REP-07-0569. Epub 2008 Jun 24.
Upon adhesion to the zona pellucida, sperm undergo regulated exocytosis of the acrosome. Although it is necessary for sperm to penetrate the zona pellucida and fertilize an egg, the acrosomal membrane fusion process is poorly understood. Complexins I and II are small, cytosolic proteins that bind to a complex of proteins termed the soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex to regulate synaptic vesicle exocytosis. Complexin-II-deficient mice are fertile but the fertility of sperm from complexin-I-deficient male mice is unclear because the mice have ataxia and cannot mate. Here, we show that the genes encoding complexins I and II are expressed in primary spermatocytes and spermatids. Complexin proteins were found in/near the developing acrosome in spermatids and in or around the acrosome of mature sperm. Cell fractionation demonstrated that complexins I and II were predominantly found in the cytosolic fraction. Furthermore, sperm from complexin-I-deficient mice had normal morphology, number, and only small differences in motility, as assessed by computer-assisted semen analysis. Complexin-I-deficient sperm capacitated normally and bound to the zona pellucida. But when sperm from complexin-I-deficient mice were inseminated into females, a defect in fertility was observed, in concordance with previous data showing that in vitro fertilization rate was also reduced. If the zona pellucida was removed prior to in vitro fertilization, fertility was normal, demonstrating that zona pellucida penetration was defective, a step requiring acrosomal exocytosis. Therefore, complexin-I-deficient sperm are subfertile due to faulty zona pellucida penetration.
精子黏附于透明带后，会发生顶体的调控性胞吐作用。尽管精子穿透透明带并使卵子受精是必要的，但顶体膜融合过程仍知之甚少。复合蛋白I和II是小的胞质蛋白，它们与一种称为可溶性N - 乙基马来酰亚胺敏感因子附着蛋白受体复合体的蛋白质复合物结合，以调节突触小泡的胞吐作用。复合蛋白II缺陷型小鼠可育，但复合蛋白I缺陷型雄性小鼠精子的生育能力尚不清楚，因为这些小鼠患有共济失调，无法交配。在此，我们表明编码复合蛋白I和II的基因在初级精母细胞和精子细胞中表达。在精子细胞发育中的顶体中以及成熟精子的顶体内或其周围发现了复合蛋白。细胞分级分离表明复合蛋白I和II主要存在于胞质部分。此外，通过计算机辅助精液分析评估，复合蛋白I缺陷型小鼠的精子形态、数量正常，仅运动能力存在微小差异。复合蛋白I缺陷型精子正常获能并与透明带结合。但是，当将复合蛋白I缺陷型小鼠的精子输精给雌性时，观察到生育缺陷，这与先前显示体外受精率也降低的数据一致。如果在体外受精前去除透明带，生育能力正常，这表明透明带穿透存在缺陷，而这一步骤需要顶体胞吐作用。因此，复合蛋白I缺陷型精子因透明带穿透缺陷而生育力低下。
