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Updated: Jul 19, 2026
Fluorimetric Techniques for the Assessment of Sperm Membranes
Published on: November 28, 2018
Sperm plasma membrane breakdown during Drosophila fertilization requires sneaky, an acrosomal membrane protein
Kathleen L Wilson1, Karen R Fitch, Blaine T Bafus
1Department of Biology, University of Washington, Seattle, Washington 98195, USA.
Abstract:
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.
Insights
In Drosophila fertilization, sperm enter eggs intact. The sneaky (snky) gene is crucial for sperm plasma membrane breakdown (PMBD) and male fertility, with its protein localized to the acrosome.
Area of Science:
- Developmental Biology
- Reproductive Biology
- Molecular Genetics
Background:
- Fertilization typically involves sperm-egg membrane fusion, but Drosophila sperm enter eggs with intact membranes.
- Sperm plasma membrane breakdown (PMBD) and activation occur post-entry in the egg cytoplasm.
- Mutations in the sneaky (snky) gene were previously linked to male sterility due to failed PMBD.
Purpose of the Study:
- To investigate the role of the sneaky (snky) gene in Drosophila sperm activation and male fertility.
- To elucidate the function of the Snky protein and its localization during fertilization.
- To understand the unique mechanism of sperm entry and activation in Drosophila.
Main Methods:
- Demonstrating the persistence of plasma membrane proteins in snky mutant sperm after egg entry.
- Analyzing snky gene expression in testes and characterizing the Snky protein's predicted structure.
- Utilizing a Snky-Green fluorescent protein (Snky-GFP) fusion to track protein and acrosome localization during fertilization.
Main Results:
- Persistence of a plasma membrane protein around snky sperm heads confirmed failed PMBD.
- Snky is expressed in testes and encodes an integral membrane protein with specific domains.
- Snky-GFP localized to the acrosome, revealing it as a paternally inherited structure that induces sperm plasma membrane changes via Snky, independent of exocytosis.
Conclusions:
- The sneaky (snky) gene is essential for sperm plasma membrane breakdown (PMBD) and male fertility in Drosophila.
- The Drosophila acrosome, containing Snky, is a paternally inherited structure that actively modifies the sperm plasma membrane for activation.
- The function of Snky and the acrosome in Drosophila suggests conserved mechanisms for membrane fusion and sperm activation across species, including humans.
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