A newly evolved gene is essential for efficient sperm entry into eggs in Drosophila melanogaster

Abstract

New genes arise through a variety of evolutionary processes and provide raw material for adaptation in the face of both natural and sexual selection. De novo evolved genes emerge from previously non-protein-coding DNA sequences, and many such genes are expressed in male reproductive structures. In Drosophila melanogaster, several putative de novo genes have evolved essential roles in spermatogenesis, but whether such genes can also impact sperm function beyond the male has not been investigated. We identified a putative de novo gene, katherine johnson (kj), that is required for high levels of male fertility. Males that do not express kj produce and transfer sperm that are stored normally in females, but sperm from these males enter eggs with severely reduced efficiency. Using a tagged transgenic rescue construct, we observed that KJ protein localizes to the nuclear periphery in various stages of spermatogenesis, but is not detectable in mature sperm. These data suggest that kj exerts an effect on sperm development, the loss of which results in reduced fertilization ability. While previous bioinformatic analyses suggested the kj gene was restricted to the melanogaster group of Drosophila, we identified putative orthologs with conserved synteny, male-biased expression, and predicted protein features across the genus, as well as instances of gene loss in some lineages. Thus, kj potentially arose in the Drosophila common ancestor and subsequently evolved an essential role in D. melanogaster. Our results demonstrate a new aspect of male reproduction that has been shaped by new gene evolution and provide a molecular foothold for further investigating the mechanism of sperm entry into eggs in Drosophila.