Drosophila sperm swim backwards in the female reproductive tract and are activated via TRPP2 ion channels

Background

Sperm have but one purpose, to fertilize an egg. In various species includingDrosophila melanogaster female sperm storage is anecessary step in the reproductive process. Amo is a homolog of the humantransient receptor potential channel TRPP2 (also known as PKD2), which ismutated in autosomal dominant polycystic kidney disease. In flies Amo isrequired for sperm storage. Drosophila males with Amomutations produce motile sperm that are transferred to the uterus but theydo not reach the female storage organs. Therefore Amo appears to be amediator of directed sperm motility in the female reproductive tract but theunderlying mechanism is unknown.

Methodology/Principal Findings

Amo exhibits a unique expression pattern during spermatogenesis. Inspermatocytes, Amo is restricted to the endoplasmic reticulum (ER) whereasin mature sperm, Amo clusters at the distal tip of the sperm tail. Here weshow that flagellar localization of Amo is required for sperm storage. Thisraised the question of how Amo at the rear end of sperm regulates forwardmovement into the storage organs. In order to address this question, we usedin vivo imaging of dual labelled sperm to demonstratethat Drosophila sperm navigate backwards in the femalereproductive tract. In addition, we show that sperm exhibit hyperactivationupon transfer to the uterus. Amo mutant sperm remaincapable of reverse motility but fail to display hyperactivation and directedmovement, suggesting that these functions are required for sperm storage inflies.

Conclusions/Significance

Amo is part of a signalling complex at the leading edge of the sperm tailthat modulates flagellar beating and that guides a backwards path into thestorage organs. Our data support an evolutionarily conserved role for TRPP2channels in cilia.