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The Drosophila melanogaster seminal fluid protein Acp62F is a protease inhibitor that is toxic upon ectopic
Oliver Lung1, Uyen Tram, Casey M Finnerty
1Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853, USA.
Abstract:
Drosophila melanogaster seminal fluid proteins stimulate sperm storage and egg laying in the mated female but also cause a reduction in her life span. We report here that of eight Drosophila seminal fluid proteins (Acps) and one non-Acp tested, only Acp62F is toxic when ectopically expressed. Toxicity to preadult male or female Drosophila occurs upon one exposure, whereas multiple exposures are needed for toxicity to adult female flies. Of the Acp62F received by females during mating, approximately 10% enters the circulatory system while approximately 90% remains in the reproductive tract. We show that in the reproductive tract, Acp62F localizes to the lumen of the uterus and the female's sperm storage organs. Analysis of Acp62F's sequence, and biochemical assays, reveals that it encodes a trypsin inhibitor with sequence and structural similarities to extracellular serine protease inhibitors from the nematode Ascaris. In light of previous results demonstrating entry of Acp62F into the mated female's hemolymph, we propose that Acp62F is a candidate for a molecule to contribute to the Acp-dependent decrease in female life span. We propose that Acp62F's protease inhibitor activity exerts positive protective functions in the mated female's reproductive tract but that entry of a small amount of this protein into the female's hemolymph could contribute to the cost of mating.
Insights
Drosophila seminal fluid protein Acp62F is toxic and acts as a trypsin inhibitor. While protective in the reproductive tract, its entry into the hemolymph may reduce female lifespan.
Area of Science:
- Reproductive Biology
- Toxicology
- Molecular Biology
Background:
- Seminal fluid proteins (Acps) in Drosophila melanogaster influence female physiology, including egg laying and lifespan.
- While beneficial effects are known, some Acps reduce female lifespan, but the specific toxic molecules remain largely unidentified.
Purpose of the Study:
- To identify toxic seminal fluid proteins in Drosophila melanogaster.
- To investigate the mechanism of toxicity and localization of the toxic protein Acp62F.
- To evaluate the role of Acp62F in the mating-associated decrease in female lifespan.
Main Methods:
- Ectopic expression of eight Acps and one non-Acp to assess toxicity.
- Exposure experiments on pre-adult and adult male and female flies.
- Tracking the distribution of Acp62F within the female reproductive tract and circulatory system post-mating.
- Sequence analysis and biochemical assays to determine Acp62F's enzymatic activity.
Main Results:
- Only Acp62F exhibited toxicity upon ectopic expression.
- Toxicity varied with developmental stage and exposure frequency; pre-adults were sensitive to single exposure, adults to multiple.
- Acp62F primarily localized to the female reproductive tract (90%), with a small fraction (10%) entering the hemolymph.
- Acp62F was identified as a trypsin inhibitor with similarities to nematode serine protease inhibitors.
Conclusions:
- Acp62F is a toxic seminal fluid protein contributing to reduced female lifespan in Drosophila melanogaster.
- Its protease inhibitor activity offers reproductive tract protection but systemic entry may incur a fitness cost.
- Acp62F is a strong candidate for mediating the negative effects of mating on female longevity.
