Male-derived transcripts isolated from the mated female reproductive tract in Drosophila melanogaster

In species with internal fertilization, sperm, and seminal fluid are transferred from male to female during mating. While both sperm and seminal fluid contain various types of molecules, including RNA, the role of most of these molecules in the coordination of fertilization or in other possible functions is poorly understood. In Drosophila, exosomes from the accessory gland, which produces seminal fluid, are transferred to females, but their potential cargoes have not been described. Moreover, while the RNA composition of sperm has been described in several mammalian species, little work on this problem has occurred in Drosophila. Here we use single nucleotide polymorphism differences between males and females from a set of highly inbred lines of D. melanogaster, and transcriptome data from the female reproductive tract, sperm, testis, and accessory gland, to investigate the potential origin, male vs female, RNA molecules isolated from 3 female reproductive tract organs, the seminal receptacle and spermatheca, which store sperm, and the parovaria, which does not. We find that mated females carry male-derived transcripts from many genes, including those that are markers of the accessory gland and known seminal fluid proteins. Our observations also support the idea that intact sperm transcripts can be isolated from the female sperm storage organs.

Identifying candidate de novo genes expressed in the somatic female reproductive tract of Drosophila melanogaster

Most eukaryotic genes have been vertically transmitted to the present from distant ancestors. However, variable gene number across species indicates that gene gain and loss also occurs. While new genes typically originate as products of duplications and rearrangements of preexisting genes, putative de novo genes-genes born out of ancestrally nongenic sequence-have been identified. Previous studies of de novo genes in Drosophila have provided evidence that expression in male reproductive tissues is common. However, no studies have focused on female reproductive tissues. Here we begin addressing this gap in the literature by analyzing the transcriptomes of 3 female reproductive tract organs (spermatheca, seminal receptacle, and parovaria) in 3 species-our focal species, Drosophila melanogaster-and 2 closely related species, Drosophila simulans and Drosophila yakuba, with the goal of identifying putative D. melanogaster-specific de novo genes expressed in these tissues. We discovered several candidate genes, located in sequence annotated as intergenic. Consistent with the literature, these genes tend to be short, single exon, and lowly expressed. We also find evidence that some of these genes are expressed in other D. melanogaster tissues and both sexes. The relatively small number of intergenic candidate genes discovered here is similar to that observed in the accessory gland, but substantially fewer than that observed in the testis.

Identifying candidate de novo genes expressed in the somatic female reproductive tract of Drosophila melanogaster

Most eukaryotic genes have been vertically transmitted to the present from distant ancestors. However, variable gene number across species indicates that gene gain and loss also occurs. While new genes typically originate as products of duplications and rearrangements of pre-existing genes, putative de novo genes - genes born out of previously non-genic sequence - have been identified. Previous studies of de novo genes in Drosophila have provided evidence that expression in male reproductive tissues is common. However, no studies have focused on female reproductive tissues. Here we begin addressing this gap in the literature by analyzing the transcriptomes of three female reproductive tract organs (spermatheca, seminal receptacle, and parovaria) in three species - our focal species, D. melanogaster - and two closely related species, D. simulans and D. yakuba , with the goal of identifying putative D. melanogaster -specific de novo genes expressed in these tissues. We discovered several candidate genes, which, consistent with the literature, tend to be short, simple, and lowly expressed. We also find evidence that some of these genes are expressed in other D. melanogaster tissues and both sexes. The relatively small number of candidate genes discovered here is similar to that observed in the accessory gland, but substantially fewer than that observed in the testis.

Drosophila female reproductive glands contribute to mating plug composition and the timing of sperm ejection

Reproductive traits that influence female remating and competitive fertilization rapidly evolve in response to sexual selection and sexual conflict. One such trait, observed across diverse animal taxa, is the formation of a structural plug inside the female reproductive tract (FRT), either during or shortly after mating. In Drosophila melanogaster, male seminal fluid forms a mating plug inside the female bursa, which has been demonstrated to influence sperm entry into storage and latency of female remating. Processing of the plug, including its eventual ejection from the female's reproductive tract, influences the competitive fertilization success of her mates and is mediated by female × male genotypic interactions. However, female contributions to plug formation and processing have received limited attention. Using developmental mutants that lack glandular FRT tissues, we reveal that these tissues are essential for mating plug ejection. We further use proteomics to demonstrate that female glandular proteins, and especially proteolytic enzymes, contribute to mating plug composition and have a widespread impact on plug formation and composition. Together, these phenotypic and molecular data identify female contributions to intersexual interactions that are a potential mechanism of post-copulatory sexual selection.