Wilson Kathleen L, Fitch Karen R, Bafus Blaine T, Wakimoto Barbara T
Department of Biology, University of Washington, Seattle, Washington 98195, USA.
Development. 2006 Dec;133(24):4871-9. doi: 10.1242/dev.02671. Epub 2006 Nov 8.
Fertilization typically involves membrane fusion between sperm and eggs. In Drosophila, however, sperm enter eggs with membranes intact. Consequently, sperm plasma membrane breakdown (PMBD) and subsequent events of sperm activation occur in the egg cytoplasm. We previously proposed that mutations in the sneaky (snky) gene result in male sterility due to failure in PMBD. Here we support this proposal by demonstrating persistence of a plasma membrane protein around the head of snky sperm after entry into the egg. We further show that snky is expressed in testes and encodes a predicted integral membrane protein with multiple transmembrane domains, a DC-STAMP-like domain, and a variant RING finger. Using a transgene that expresses an active Snky-Green fluorescent protein fusion (Snky-GFP), we show that the protein is localized to the acrosome, a membrane-bound vesicle located at the apical tip of sperm. Snky-GFP also allowed us to follow the fate of the protein and the acrosome during fertilization. In many animals, the acrosome is a secretory vesicle with exocytosis essential for sperm penetration through the egg coats. Surprisingly, we find that the Drosophila acrosome is a paternally inherited structure. We provide evidence that the acrosome induces changes in sperm plasma membrane, exclusive of exocytosis and through the action of the acrosomal membrane protein Snky. Existence of testis-expressed Snky-like genes in many animals, including humans, suggests conserved protein function. We relate the characteristics of Drosophila Snky, acrosome function and sperm PMBD to membrane fusion events that occur in other systems.
受精通常涉及精子与卵子之间的膜融合。然而，在果蝇中，精子进入卵子时膜保持完整。因此，精子质膜破裂（PMBD）及随后的精子激活事件发生在卵细胞质中。我们之前提出，偷偷摸摸（snky）基因的突变会导致雄性不育，原因是PMBD失败。在这里，我们通过证明snky精子进入卵子后质膜蛋白在头部周围持续存在来支持这一观点。我们进一步表明，snky在睾丸中表达，编码一种预测的整合膜蛋白，具有多个跨膜结构域、一个DC-STAMP样结构域和一个变异的环指结构。使用表达活性Snky-绿色荧光蛋白融合体（Snky-GFP）的转基因，我们表明该蛋白定位于顶体，顶体是位于精子顶端的膜结合囊泡。Snky-GFP还使我们能够追踪受精过程中该蛋白和顶体的命运。在许多动物中，顶体是一种分泌囊泡，其胞吐作用对于精子穿透卵膜至关重要。令人惊讶的是，我们发现果蝇顶体是父系遗传结构。我们提供证据表明，顶体诱导精子质膜发生变化，不包括胞吐作用，且是通过顶体膜蛋白Snky的作用。包括人类在内的许多动物中存在睾丸表达的Snky样基因，这表明蛋白功能具有保守性。我们将果蝇Snky的特征、顶体功能和精子PMBD与其他系统中发生的膜融合事件联系起来。
