Fertilization is the fundamental process that initiates the development of a new individual in all sexually reproducing species. Despite its importance, our understanding of the molecular players that govern mammalian sperm–egg interaction is incomplete, partly because many of the essential factors found in nonmammalian species do not have obvious mammalian homologs. We have recently identified the lymphocyte antigen-6 (Ly6)/urokinase-type plasminogen activator receptor (uPAR) protein Bouncer as an essential fertilization factor in zebrafish [S. Herberg, K. R. Gert, A. Schleiffer, A. Pauli, Science 361, 1029–1033 (2018)]. Here, we show that Bouncer’s homolog in mammals, Sperm Acrosome Associated 4 (SPACA4), is also required for efficient fertilization in mice. In contrast to fish, in which Bouncer is expressed specifically in the egg, SPACA4 is expressed exclusively in the sperm. Male knockout mice are severely subfertile, and sperm lacking SPACA4 fail to fertilize wild-type eggs in vitro. Interestingly, removal of the zona pellucida rescues the fertilization defect of Spaca4-deficient sperm in vitro, indicating that SPACA4 is not required for the interaction of sperm and the oolemma but rather of sperm and the zona pellucida. Our work identifies SPACA4 as an important sperm protein necessary for zona pellucida penetration during mammalian fertilization.

受精是所有有性繁殖物种中启动新个体发育的基本过程。尽管它很重要，但我们对控制哺乳动物精卵相互作用的分子参与者的理解并不完整，部分原因是在非哺乳动物物种中发现的许多基本因素没有明显的哺乳动物同源物。我们最近发现淋巴细胞抗原 6 (Ly6)/尿激酶型纤溶酶原激活剂受体 (uPAR) 蛋白 Bouncer 是斑马鱼的重要受精因子 [S.赫伯格、KR Gert、A. Schleiffer、A. Pauli，科学361, 1029–1033 (2018)]。在这里，我们发现 Bouncer 在哺乳动物中的同源物 Sperm Acrosome Associated 4 (SPACA4) 也是小鼠有效受精所必需的。与鱼相比，Bouncer 专门在卵子中表达，而 SPACA4 专门在精子中表达。雄性基因敲除小鼠的生育力严重低下，缺乏 SPACA4 的精子无法在体外使野生型卵子受精。有趣的是，去除透明带可以挽救Spaca4缺陷精子的体外受精缺陷，这表明 SPACA4 不是精子和卵膜相互作用所必需的，而是精子和透明带相互作用所必需的。我们的工作确定 SPACA4 是哺乳动物受精过程中穿透透明带所必需的重要精子蛋白。