The Drosophila melanogaster seminal fluid protease "seminase" regulates proteolytic and post-mating reproductive processes

Systems biology of Haemonchus contortus - Advancing biotechnology for parasitic nematode control

Parasitic nematodes represent a substantial global burden, impacting animal health, agriculture and economies worldwide. Of these worms, Haemonchus contortus - a blood-feeding nematode of ruminants - is a major pathogen and a model for molecular and applied parasitology research. This review synthesises some key advances in understanding the molecular biology, genetic diversity and host-parasite interactions of H. contortus, highlighting its value for comparative studies with the free-living nematode Caenorhabditis elegans. Key themes include recent developments in genomic, transcriptomic and proteomic technologies and resources, which are illuminating critical molecular pathways, including the ubiquitination pathway, protease/protease inhibitor systems and the secretome of H. contortus. Some of these insights are providing a foundation for identifying essential genes and exploring their potential as targets for novel anthelmintics or vaccines, particularly in the face of widespread anthelmintic resistance. Advanced bioinformatic tools, such as machine learning (ML) algorithms and artificial intelligence (AI)-driven protein structure prediction, are enhancing annotation capabilities, facilitating and accelerating analyses of gene functions, and biological pathways and processes. This review also discusses the integration of these tools with cutting-edge single-cell sequencing and spatial transcriptomics to dissect host-parasite interactions at the cellular level. The discussion emphasises the importance of curated databases, improved culture systems and functional genomics platforms to translate molecular discoveries into practical outcomes, such as novel interventions. New research findings and resources not only advance research on H. contortus and related nematodes but may also pave the way for innovative solutions to the global challenges with anthelmintic resistance.

Expanded characterization and localization of male seminal fluid proteins within the female reproductive tract of the dengue vector mosquito Aedes aegypti

Aedes aegypti mosquitoes transmit numerous viruses that impact human health. Contemporary biological control programs aim to reduce Aedes fertility despite our limited understanding of interactions between the sexes required for reproduction. During mating, males transfer seminal fluid proteins (SFPs) to females which alter their post-mating behavior, physiology and gene regulation, but the contribution of individual SFPs to fertility remains uncharacterized. In Drosophila, a small subset of SFPs localize to the sperm storage organs and oviducts or enter the hemolymph which suggests their participation in specific post-mating processes. We used mass spectrometry-based proteomics in conjunction with whole animal heavy labelling to expand the characterization of the Ae. aegypti ejaculate and identify SFPs that leave the site of insemination and localize to other female tissues. We identified 1031 ejaculate proteins, including a suite of novel SFPs. The expanded ejaculate proteome shows low conservation amongst SFPs when compared to insect model Drosophila, consistent with rapid evolutionary turnover at the genetic and proteomic levels. Further, we identify 25 SFPs that localize to the spermathecae, oviducts, and/or enter the hemolymph. This study expands our knowledge of the Ae. aegypti seminal fluid proteome and identifies candidate SFPs that may have tissue-specific, postcopulatory roles which support fertility. SIGNIFICANCE: Male-derived seminal fluid proteins (SFPs), transferred to females along with sperm during mating, are essential for the fertility of a mating pair. SFPs in aggregate induce several physiological and behavioral changes in mated females. Studies in the insect model Drosophila have shown that individual SFPs often participate in specific post-mating processes. In the dengue vector mosquito Aedes aegypti, 177 high confidence SFPs have been identified, but the contribution of individual SFPs in female fertility has yet not been characterized. In Drosophila, a small subset of SFPs leave the site of insemination and localize to the oviduct and sperm storage organs of the female reproductive tract or are transported to the female hemolymph, with patterns of SFP localization suggesting participation in a specific post-mating process. We used MS/MS proteomic characterization coupled with whole animal heavy labeling to expand characterization of the Ae. aegypti ejaculate proteome, increasing the number of known ejaculate proteins to 1378, including identification of 40 novel SFPs. Further, we identified 25 SFPs that leave the site of insemination and localize to the oviducts and/or spermathecae or enter the hemolymph, which can now be assessed for potential tissue-specific functions in female fertility.

Identification of seminal fluid proteins and reproductive function of trypsin-1 in male Plutella xylostella

Insect seminal fluid proteins (SFPs) are primary factors affecting physiology and behavior in both sexes, making them valuable targets for pest control. However, SFPs have not been fully characterized in the Plutella xylostella, a global pest that attacks cruciferous crops. Here, 75 putative SFPs were identified in P. xylostella, compared to 10 orthologs in Drosophila melanogaster, 10 in Nilaparvata lugens, 5 in Apis mellifera, and 43 in Heliconius melpomene. Analyses of Ka/Ks suggested that SFPs had high evolution rates. Proteases (22/75, 29.3 %) accounted for the highest proportion of P. xylostella SFPs, including 16 trypsins. The phylogenetic analysis showed that most trypsins from P. xylostella and H. melpomene belonged to the same cluster. SFP04 (trypsin-1) was orthologous to the SFP ADJ58550.1 in H. melpomene. PxTry1 was specifically expressed in adult males and their accessory glands but was also detected in females after mating. A CRISPR/Cas9-induced PxTry1 homozygous mutant strain with a 22-base pair nucleotides insertion was generated. PxTry1 deletion resulted in swollen testes, smaller spermatophores, and abnormal sperm, thus reducing the P. xylostella egg production and hatching. These results clarify the role of insect SFPs in evolution and reproduction and identify a promising target for pest control based on genetic regulation.

An orphan gene is essential for efficient sperm entry into eggs in Drosophila melanogaster

While spermatogenesis has been extensively characterized in the Drosophila melanogaster model system, very little is known about the genes required for fly sperm entry into eggs. We identified a lineage-specific gene, which we named katherine johnson (kj), that is required for efficient fertilization. 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 the KJ protein localizes around the edge of the nucleus at various stages of spermatogenesis but is undetectable in mature sperm. These data suggest that kj exerts an effect on sperm development, the loss of which results in reduced fertilization ability. Interestingly, KJ protein lacks detectable sequence similarity to any other known protein, suggesting that kj could be a lineage-specific orphan gene. While previous bioinformatic analyses indicated that kj 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 likely instances of gene loss in some lineages. Thus, kj was likely present in the Drosophila common ancestor. It is unclear whether its role in fertility had already evolved at that time or developed later in the lineage leading to D. melanogaster. Our results demonstrate a new aspect of male reproduction that has been shaped by a lineage-specific gene and provide a molecular foothold for further investigating the mechanism of sperm entry into eggs in Drosophila.

Disruption of Spodoptera exigua serine protease 2 (Ser2) results in male sterility by CRISPR/Cas9 technology

BACKGROUND

Sperm development and behavior present promising targets for environmentally safer, target-specific biorational control strategies. Serine protease in seminal fluid proteins plays a crucial role in the post-mating reproductive processes of lepidopteran pest insects. The serine protease 2 has been identified as the initiatorin of the seminal fluid protein in Lepidoptera, and its loss of function leads to male sterility. Nevertheless, the genetic pattern of this gene mutation and the impacts of various mutant genotypes on the hatchability of the eggs of pests remain unclear.

RESULTS

This study focused on the cloning of Spodoptera exigua serine protease 2 (SeSer2), which is specifically expressed in male moths. The open reading frame of SeSer2 consists of 843 nucleotides, encoding 280 amino acids with structural characteristics typical of serine proteases in the S1 family. To validate the functional role of SeSer2 in the fertility of S. exigua, a targeted ~3574-bp deletion of SeSer2 was introduced using the CRISPR/Cas9 genome editing system, leading to premature truncation of the SeSer2 protein. The SeSer2 mutation had no significant impact on the growth and development of individuals of either sex. However, disruption of SeSer2 resulted in heritable male sterility. Although females mated with SeSer2-/- (SeSer2 knockout homozygote) males laid eggs normally, these eggs failed to hatch. SeSer2+/- (SeSer2 knockout heterozygote) male moths crossed with female moths produced viable offspring, indicating the gene's recessive role in egg hatching.

CONCLUSION

These findings strongly support the conclusion that the Ser2 gene is essential for male reproductive success in diverse lepidopterans. Targeting the Ser2 gene holds promise as a foundational element of a novel pest control strategy. © 2024 Society of Chemical Industry.

An orphan gene is essential for efficient sperm entry into eggs in Drosophila melanogaster

While spermatogenesis has been extensively characterized in the Drosophila melanogaster model system, very little is known about the genes required for fly sperm entry into eggs. We identified a lineage-specific gene, which we named katherine johnson (kj), that is required for efficient fertilization. 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 the KJ protein localizes around the edge of the nucleus at various stages of spermatogenesis but is undetectable in mature sperm. These data suggest that kj exerts an effect on sperm development, the loss of which results in reduced fertilization ability. Interestingly, KJ protein lacks detectable sequence similarity to any other known protein, suggesting that kj could be a lineage-specific orphan gene. While previous bioinformatic analyses indicated that kj 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 likely instances of gene loss in some lineages. Thus, kj was likely present in the Drosophila common ancestor and subsequently evolved an essential role in fertility in D. melanogaster. Our results demonstrate a new aspect of male reproduction that has been shaped by a lineage-specific gene and provide a molecular foothold for further investigating the mechanism of sperm entry into eggs in Drosophila.

Male-derived phospholipase A2 enhances WD46 expression and increases fertility in Ophraella communa

Successful bisexual reproduction requires interactions between males and females. Male-derived seminal fluid proteins (SFPs) transferred to females during mating profoundly affect females from pre- to post-mating, and the subsequent shift in female physiology enhances their fertility. SFPs have important evolutionary implications for the fitness of many insects. However, little is known about how females respond to male SFPs. In this study, we identified a male-derived SFP-phospholipase A2 (PLA2) in Ophraella communa. PLA2 is a vital enzyme in eicosanoid biosynthesis; however, it has not been identified as an insect SFP. We found that OcPLA2 is specifically expressed in males, especially in the male accessory glands (MAGs); it is transferred to the female during mating and functions as an SFP to enhance fertility. The expression of a female-derived gene encoding the WD repeat-containing protein 46 (WD46) was upregulated when OcPLA2 entered the female reproductive tract, and this contributed to female egg production by increasing triacylglycerol lipase (TGL) gene expression and the triglyceride (TG) content. This is the first study to identify PLA2 as an SFP in insects. Our findings also shed light on the regulatory role of OcPLA2 in beetle reproduction; the expression of OcPLA2 is initially correlated with female WD46 expression and later with the decline in TGL gene expression and the TG content. This represents a unique mechanism of reproductive regulation by an SFP.

Exploring the role of the ovary-serine protease gene in the female fertility of the diamondback moth using CRISPR/Cas9

BACKGROUND

Oogenesis is a complex pathway necessary for proper female reproduction in insects. Ovary-serine protease (Osp) is a homologous gene of serine protease Nudel (SpNudel) and plays an essential role in the oogenesis and ovary development of Drosophila melanogaster. However, the function of Osp is not determined in Plutella xylostella, a highly destructive pest of cruciferous crops.

RESULTS

The PxOsp gene comprises a 5883-bp open-reading frame that encodes a protein consisting of 1994 amino acids, which contain four conserved domains. PxOsp exhibited a high relative expression in adult females with a specific expression in the ovary. Through the utilization of CRISPR/Cas9 technology, homozygous mutants of PxOsp were generated. These homozygous mutant females produced fewer eggs (average of 56 eggs/female) than wild-type (WT) females (average of 97 eggs/female) when crossed with WT males, and these eggs failed to hatch. Conversely, mutant males produced normal progeny when crossed with WT females. The ovarioles in homozygous mutant females were significantly shorter (5.02 mm in length) and contained fewer eggs (average of 3 eggs/ovariole) than WT ovarioles (8.09 mm in length with an average of 8 eggs/ovariole). Moreover, eggs laid by homozygous mutant females were fragile, with irregular shapes, and were unable to maintain structural integrity due to eggshell ruptures. However, no significant differences were observed between WT and mutant individuals regarding developmental duration, pupal weight, and mating behavior.

CONCLUSION

Our study suggesteds that PxOsp plays a vital role in female reproduction, particularly in ovary and egg development. Disrupting PxOsp results in recessive female sterility while leaving the male reproductive capability unaffected. This report represents the first study of a haplosufficient gene responsible for female fertility in lepidopteran insects. Additionally, these findings emphasize PxOsp as a potential target for genetically-based pest management of P. xylostella. © 2024 Society of Chemical Industry.

A sperm-activating trypsin-like protease from the male reproductive tract of Spodoptera litura: Proteomic identification, sequence characterization, gene expression profile, RNAi and the effects of ionizing radiation

Like other lepidopteran insects, males of the tobacco cutworm moth, Spodoptera litura produce two kinds of spermatozoa, eupyrene (nucleate) and apyrene (anucleate) sperm. Formed in the testis, both kinds of sperm are released into the male reproductive tract in an immature form and are stored in the duplex region of the tract. Neither type of sperm is motile at this stage. When stored apyrene sperm from the duplex are treated in vitro with an extract of the prostatic region of the male tract, or with mammalian trypsin, they become motile; activation is greater and achieved more rapidly with increasing concentration of extract or enzyme. The activating effect of prostatic extract is blocked by soybean trypsin inhibitor (SBTI), also in a dose-dependent way. These results suggest that the normal sperm-activating process is due to an endogenous trypsin-like protease produced in the prostatic region. Proteomic analysis of S. litura prostatic extracts revealed a Trypsin-Like Serine Protease, TLSP, molecular weight 27 kDa, whose 199-residue amino acid sequence is identical to that of a predicted protein from the S. litura genome and is highly similar to predicted proteins encoded by genes in the genomes of several other noctuid moth species. Surprisingly, TLSP is only distantly related to Serine Protease 2 (initiatorin) of the silkmoth, Bombyx mori, the only identified lepidopteran protein so far shown to activate sperm. TLSP has features typical of secreted proteins, probably being synthesized as an inactive precursor zymogen, which is later activated by proteolytic cleavage. cDNA was synthesized from total RNA extracted from the prostatic region and was used to examine TLSP expression using qPCR. tlsp mRNA was expressed in both the prostatic region and the accessory glands of the male tract. Injection of TLSP-specific dsRNA into adult males caused a significant reduction after 24 h in tlsp mRNA levels in both locations. The number of eggs laid by females mated to adult males that were given TLSP dsRNA in 10 % honey solution, and the fertility (% hatched) of the eggs were reduced. Injecting pupae with TLSP dsRNA caused the later activation of apyrene sperm motility by adult male prostatic extracts to be significantly reduced compared to controls. Exposure of S. litura pupae to ionizing radiation significantly reduced expression of tlsp mRNA in the prostatic part and accessory gland of irradiated males in both the irradiated generation and also in their (unirradiated) F1 progeny. The implications of these findings for the use of the inherited sterility technique for the control of S. litura and other pest Lepidoptera are discussed.

Sast1-mediated manifold effects inhibit Plutella xylostella fertility

BACKGROUND

Plutella xylostella (Linnaeus) is a destructive pest of cruciferous crops due to its strong reproductive capacity and extensive resistance to pesticides. Seminal fluid proteins (SFPs) are the main effective factors that determine the reproductive physiology and behaviour of both sexes. Although an increasing number of SFPs have been identified, the effects of astacins in SFPs on agricultural pests have not yet been reported. Here, we elucidated the mechanisms by which Sast1 (seminal astacin 1) regulates the fertility of Plutella xylostella (L.).

RESULTS

PxSast1 was specifically expressed in the testis and accesssory gland. CRISPR/Cas9-induced PxSast1 knockout successfully constructed two homozygous mutant strains. Sast1 impaired the fertility of P. xylostella by separately regulating the reproductive capacity of males and females. Loss of PxSast1, on the one hand, significantly decreased the ability of males to mate and fertilize, mainly manifested as shortened mating duration, reduced mating competitiveness and decreased eupyrene sperm production; on the other hand, it significantly inhibited the expression of chorion genes in females, resulting in oogenesis deficits. Simultaneously, for mated females, the differentially expressed genes in signalling pathways related to oogenesis and chorion formation were significantly enriched after PxSast1 knockout.

CONCLUSION

These analyses of the functions of PxSast1 as the regulator of spermatogenesis and oogenesis establish its importance in the fertility process of P. xylostella, as well as its potential as a promising target for genetic regulation-based pest control. © 2024 Society of Chemical Industry.

The seminal odorant binding protein Obp56g is required for mating plug formation and male fertility in Drosophila melanogaster

In Drosophila melanogaster and other insects, the seminal fluid proteins (SFPs) and male sex pheromones that enter the female with sperm during mating are essential for fertility and induce profound post-mating effects on female physiology. The SFPs in D. melanogaster and other taxa include several members of the large gene family known as odorant binding proteins (Obps). Work in Drosophila has shown that some Obp genes are highly expressed in the antennae and can mediate behavioral responses to odorants, potentially by binding and carrying these molecules to odorant receptors. These observations have led to the hypothesis that the seminal Obps might act as molecular carriers for pheromones or other compounds important for male fertility, though functional evidence in any species is lacking. Here, we used functional genetics to test the role of the seven seminal Obps in D. melanogaster fertility and the post-mating response (PMR). We found that Obp56g is required for male fertility and the induction of the PMR, whereas the other six genes are dispensable. We found males lacking Obp56g fail to form a mating plug in the mated female's reproductive tract, leading to ejaculate loss and reduced sperm storage, likely due to its expression in the male ejaculatory bulb. We also examined the evolutionary history of these seminal Obp genes, as several studies have documented rapid evolution and turnover of SFP genes across taxa. We found extensive lability in gene copy number and evidence of positive selection acting on two genes, Obp22a and Obp51a. Comparative RNAseq data from the male reproductive tract of multiple Drosophila species revealed that Obp56g shows high male reproductive tract expression in a subset of taxa, though conserved head expression across the phylogeny. Together, these functional and expression data suggest that Obp56g may have been co-opted for a reproductive function over evolutionary time.

SPSL1 is essential for spermatophore formation and sperm activation in Spodoptera frugiperda

The reproductive process in various species has undergone evolutionary adaptations at both the physiological and molecular levels, playing a significant role in maintaining their populations. In lepidopteran insects, the spermatophore is a unique structure formed in the female reproductive system, in which sperm storage and activation take place. It is known that the formation of the spermatophore is regulated by seminal fluid proteins derived from males. However, studies investigating the genetic mechanisms behind spermatophore formation in lepidopterans have been limited. In this study, our focus was on SPSL1, a gene that encodes a trypsin-type seminal fluid protein in Spodoptera frugiperda, a pest species with global invasive tendencies. Our findings revealed that SPSL1 expression was predominantly observed in the male reproductive tracts, and the disruption of this gene resulted in male sterility. Surprisingly, fluorescence analysis indicated that the absence of SPSL1 did not affect spermatogenesis or sperm migration within the male reproductive system. However, when females mated with SPSL1-mutant males, several defects were observed. These included disruptions in spermatophore formation, sperm activation in the copulatory bursae, and sperm migration into the spermathecae. Additionally, mass spectrometry analysis highlighted reduced levels of energy-related metabolites, suggesting that SPSL1 plays an essential role in promoting hydrolysis reactions during copulation. Consequently, our study demonstrates that SPSL1 is crucial for male fertility due to its functions in spermatophore formation and sperm activation. This research provides valuable insights into the genetic factors underlying reproductive processes in lepidopteran insects and sheds light on potential strategies for controlling invasive pest populations.

Knockout of ovary serine protease Leads to Ovary Deformation and Female Sterility in the Asian Corn Borer, Ostrinia furnacalis

Oogenesis in insects is a carefully orchestrated process, facilitating the formation of female gametes, which is regulated by multiple extrinsic and intrinsic factors, including ovary serine protease (Osp). As a member of the serine protease family, Osp is a homolog of Nudel, a maternally required protease defining embryonic dorsoventral polarity in Drosophila. In this study, we used CRISPR/Cas9-mediated mutagenesis to functionally characterize Osp in the Asian corn borer, Ostrinia furnacalis, a devastating maize pest throughout Asia and Australia. Building on previous knowledge, we hypothesized that knockout of Osp would disrupt embryonic development in O. furnacalis females. To examine this overarching hypothesis, we (1) cloned and characterized Osp from O. furnacalis, (2) designed target sites on exons 1 and 4 to construct a CRISPR/Cas9 mutagenesis system, and (3) documented phenotypic impacts among O. furnacalis Osp mutants. As a result, we (1) examined the temporal-spatial expression profiles of OfOsp, which has an open reading frame of 5648 bp in length and encodes a protein of 1873 amino acids; (2) established O. furnacalis Osp mutants; and (3) documented recessive, female-specific sterility among OfOspF mutants, including absent or deformed oviducts and reduced fertility in female but not male mutants. Overall, the combined results support our initial hypothesis that Osp is required for embryonic development, specifically ovarian maturation, in O. furnacalis females. Given its substantial impacts on female sterility, Osp provides a potential target for the Sterile Insect Technique (SIT) to manage Lepidoptera pests in general and the species complex Ostrinia in particular.

Post-Mating Responses in Insects Induced by Seminal Fluid Proteins and Octopamine

Following insect mating, females often exhibit a series of physiological, behavioral, and gene expression changes. These post-mating responses (PMRs) are induced by seminal fluid components other than sperm, which not only form network proteins to assist sperm localization, supplement female-specific protein requirements, and facilitate the formation of specialized functional structures, but also activate neuronal signaling pathways in insects. This review primarily discusses the roles of seminal fluid proteins (SFPs) and octopamine (OA) in various PMRs in insects. It explores the regulatory mechanisms and mediation conditions by which they trigger PMRs, along with the series of gene expression differences they induce. Insect PMRs involve a transition from protein signaling to neuronal signaling, ultimately manifested through neural regulation and gene expression. The intricate signaling network formed as a result significantly influences female behavior and organ function, contributing to both successful reproduction and the outcomes of sexual conflict.

Genome-Wide Analysis of Haemonchus contortus Proteases and Protease Inhibitors Using Advanced Informatics Provides Insights into Parasite Biology and Host-Parasite Interactions

Biodiversity within the animal kingdom is associated with extensive molecular diversity. The expansion of genomic, transcriptomic and proteomic data sets for invertebrate groups and species with unique biological traits necessitates reliable in silico tools for the accurate identification and annotation of molecules and molecular groups. However, conventional tools are inadequate for lesser-known organismal groups, such as eukaryotic pathogens (parasites), so that improved approaches are urgently needed. Here, we established a combined sequence- and structure-based workflow system to harness well-curated publicly available data sets and resources to identify, classify and annotate proteases and protease inhibitors of a highly pathogenic parasitic roundworm (nematode) of global relevance, called Haemonchus contortus (barber's pole worm). This workflow performed markedly better than conventional, sequence-based classification and annotation alone and allowed the first genome-wide characterisation of protease and protease inhibitor genes and gene products in this worm. In total, we identified 790 genes encoding 860 proteases and protease inhibitors representing 83 gene families. The proteins inferred included 280 metallo-, 145 cysteine, 142 serine, 121 aspartic and 81 "mixed" proteases as well as 91 protease inhibitors, all of which had marked physicochemical diversity and inferred involvements in >400 biological processes or pathways. A detailed investigation revealed a remarkable expansion of some protease or inhibitor gene families, which are likely linked to parasitism (e.g., host-parasite interactions, immunomodulation and blood-feeding) and exhibit stage- or sex-specific transcription profiles. This investigation provides a solid foundation for detailed explorations of the structures and functions of proteases and protease inhibitors of H. contortus and related nematodes, and it could assist in the discovery of new drug or vaccine targets against infections or diseases.

The seminal odorant binding protein Obp56g is required for mating plug formation and male fertility in Drosophila melanogaster

In Drosophila melanogaster and other insects, the seminal fluid proteins (SFPs) and male sex pheromones that enter the female with sperm during mating are essential for fertility and induce profound post-mating effects on female physiology and behavior. The SFPs in D. melanogaster and other taxa include several members of the large gene family known as odorant binding proteins (Obps). Previous work in Drosophila has shown that some Obp genes are highly expressed in the antennae and can mediate behavioral responses to odorants, potentially by binding and carrying these molecules to odorant receptors. These observations have led to the hypothesis that the seminal Obps might act as molecular carriers for pheromones or other compounds important for male fertility in the ejaculate, though functional evidence in any species is lacking. Here, we used RNAi and CRISPR/Cas9 generated mutants to test the role of the seven seminal Obps in D. melanogaster fertility and the post-mating response (PMR). We found that Obp56g is required for male fertility and the induction of the PMR, whereas the other six genes had no effect on fertility when mutated individually. Obp56g is expressed in the male's ejaculatory bulb, an important tissue in the reproductive tract that synthesizes components of the mating plug. We found males lacking Obp56g fail to form a mating plug in the mated female's reproductive tract, leading to ejaculate loss and reduced sperm storage. We also examined the evolutionary history of these seminal Obp genes, as several studies have documented rapid evolution and turnover of SFP genes across taxa. We found extensive lability in gene copy number and evidence of positive selection acting on two genes, Obp22a and Obp51a. Comparative RNAseq data from the male reproductive tract of multiple Drosophila species revealed that Obp56g shows high male reproductive tract expression only in species of the melanogaster and obscura groups, though conserved head expression in all species tested. Together, these functional and expression data suggest that Obp56g may have been co-opted for a reproductive function over evolutionary time.

Structural and evolutionary insights into astacin metallopeptidases

The astacins are a family of metallopeptidases (MPs) that has been extensively described from animals. They are multidomain extracellular proteins, which have a conserved core architecture encompassing a signal peptide for secretion, a prodomain or prosegment and a zinc-dependent catalytic domain (CD). This constellation is found in the archetypal name-giving digestive enzyme astacin from the European crayfish Astacus astacus. Astacin catalytic domains span ∼200 residues and consist of two subdomains that flank an extended active-site cleft. They share several structural elements including a long zinc-binding consensus sequence (HEXXHXXGXXH) immediately followed by an EXXRXDRD motif, which features a family-specific glutamate. In addition, a downstream SIMHY-motif encompasses a "Met-turn" methionine and a zinc-binding tyrosine. The overall architecture and some structural features of astacin catalytic domains match those of other more distantly related MPs, which together constitute the metzincin clan of metallopeptidases. We further analysed the structures of PRO-, MAM, TRAF, CUB and EGF-like domains, and described their essential molecular determinants. In addition, we investigated the distribution of astacins across kingdoms and their phylogenetic origin. Through extensive sequence searches we found astacin CDs in > 25,000 sequences down the tree of life from humans beyond Metazoa, including Choanoflagellata, Filasterea and Ichtyosporea. We also found < 400 sequences scattered across non-holozoan eukaryotes including some fungi and one virus, as well as in selected taxa of archaea and bacteria that are pathogens or colonizers of animal hosts, but not in plants. Overall, we propose that astacins originate in the root of Holozoa consistent with Darwinian descent and that the latter genes might be the result of horizontal gene transfer from holozoan donors.

Female factors modulate Sex Peptide's association with sperm in Drosophila melanogaster

BACKGROUND

Male-derived seminal fluid proteins (SFPs) that enter female fruitflies during mating induce a myriad of physiological and behavioral changes, optimizing fertility of the mating pair. Some post-mating changes in female Drosophila melanogaster persist for ~10-14 days. Their long-term persistence is because the seminal protein that induces these particular changes, the Sex Peptide (SP), is retained long term in females by binding to sperm, with gradual release of its active domain from sperm. Several other "long-term response SFPs" (LTR-SFPs) "prime" the binding of SP to sperm. Whether female factors play a role in this process is unknown, though it is important to study both sexes for a comprehensive physiological understanding of SFP/sperm interactions and for consideration in models of sexual conflict.

RESULTS

We report here that sperm in male ejaculates bind SP more weakly than sperm that have entered females. Moreover, we show that the amount of SP, and other SFPs, bound to sperm increases with time and transit of individual seminal proteins within the female reproductive tract (FRT). Thus, female contributions are needed for maximal and appropriate binding of SP, and other SFPs, to sperm. Towards understanding the source of female molecular contributions, we ablated spermathecal secretory cells (SSCs) and/or parovaria (female accessory glands), which contribute secretory proteins to the FRT. We found no dramatic change in the initial levels of SP bound to sperm stored in mated females with ablated or defective SSCs and/or parovaria, indicating that female molecules that facilitate the binding of SP to sperm are not uniquely derived from SSCs and parovaria. However, we observed higher levels of SP (and sperm) retention long term in females whose SSCs and parovaria had been ablated, indicating secretions from these female tissues are necessary for the gradual release of Sex Peptide's active region from stored sperm.

CONCLUSION

This study reveals that the SP-sperm binding pathway is not entirely male-derived and that female contributions are needed to regulate the levels of SP associated with sperm stored in their storage sites.

Discovering novel reproductive genes in a non-model fly using de novo GridION transcriptomics

Gene discovery has important implications for investigating phenotypic trait evolution, adaptation, and speciation. Male reproductive tissues, such as accessory glands (AGs), are hotspots for recruitment of novel genes that diverge rapidly even among closely related species/populations. These genes synthesize seminal fluid proteins that often affect post-copulatory sexual selection-they can mediate male-male sperm competition, ejaculate-female interactions that modify female remating and even influence reproductive incompatibilities among diverging species/populations. Although de novo transcriptomics has facilitated gene discovery in non-model organisms, reproductive gene discovery is still challenging without a reference database as they are often novel and bear no homology to known proteins. Here, we use reference-free GridION long-read transcriptomics, from Oxford Nanopore Technologies (ONT), to discover novel AG genes and characterize their expression in the widespread dung fly, Sepsis punctum. Despite stark population differences in male reproductive traits (e.g.: Body size, testes size, and sperm length) as well as female re-mating, the male AG genes and their secretions of S. punctum are still unknown. We implement a de novo ONT transcriptome pipeline incorporating quality-filtering and rigorous error-correction procedures, and we evaluate gene sequence and gene expression results against high-quality Illumina short-read data. We discover highly-expressed reproductive genes in AG transcriptomes of S. punctum consisting of 40 high-quality and high-confidence ONT genes that cross-verify against Illumina genes, among which 26 are novel and specific to S. punctum. Novel genes account for an average of 81% of total gene expression and may be functionally relevant in seminal fluid protein production. For instance, 80% of genes encoding secretory proteins account for 74% total gene expression. In addition, median sequence similarities of ONT nucleotide and protein sequences match within-Illumina sequence similarities. Read-count based expression quantification in ONT is congruent with Illumina's Transcript per Million (TPM), both in overall pattern and within functional categories. Rapid genomic innovation followed by recruitment of de novo genes for high expression in S. punctum AG tissue, a pattern observed in other insects, could be a likely mechanism of evolution of these genes. The study also demonstrates the feasibility of adapting ONT transcriptomics for gene discovery in non-model systems.

The female Euscepes postfasciatus refractory period is induced by the male but length is determined by the female

Females of many animals mate multiple times during their lives (i.e., polyandry). The period between matings (mating interval) is called the refractory period (RP). In the West Indian sweet potato weevil (Euscepes postfasciatus), males use the ejaculate to induce the RP in females to prevent re-mating. By measuring the RP, a large variation of 1-49 days was observed. This variation may be due to the males (ejaculate quantity and quality) and females (ejaculate sensitivity/degradation ability and body size) and their interactions, but the exact mechanisms are currently unclear. Here, we investigated a tendency towards a particular female RP duration and the associated traits of males and females to test the following three factors responsible for variation in the length of the RP: male manipulation of ejaculate volume, individual differences in male ejaculation substances, and ejaculate sensitivity/degradation ability in females. We prepared virgin males and females to create mating pairs. The following day, another mate was introduced to the females, and the first RP was measured. The same procedure was used for measuring the second RP. The males were also provided with another female (second female), mated, and then the RP of the second female was measured. In addition, the relationship between the length of the RP and female fitness was investigated. The results showed that there was a significant positive correlation between the first and second RP in the focal females, while no significant correlation was observed between the RP of the first and second females induced by the same male. It was also found that the length of the RP did not affect female fitness. This indicated that the males did not adaptively manipulate ejaculation volume depending on the quality of the females, and variance in the length of the RP may be explained by variation in the female physiological ability against ejaculate.

On how to identify a seminal fluid protein: A commentary on Hurtado et al

Seminal fluid proteins (Sfps) have striking effects on the behaviour and physiology of females in many insects. Some Drosophila melanogaster Sfps are not highly or exclusively expressed in the accessory glands, but derive from, or are additionally expressed in other male reproductive tissues. The full suite of Sfps includes transferred proteins from all male reproductive tissues, regardless of expression level or presence of a signal peptide.

CRISPR/Cas9-mediated Serine protease 2 disruption induces male sterility in Spodoptera litura

Male fertility is essential for reproduction and population growth in animals. Many factors affect male fertility, such as courtship behavior, sperm quantity, and sperm motility, among others. Seminal Fluid Proteins (SFPs) are vital components of seminal fluid in the male ejaculate, which affect male fertility, sperm activation, and female ovulation. However, the knowledge of SFPs is insufficient; the function of many SFPs remains unknown, and most described functions were mainly characterized in Drosophila or other laboratory models. Here, we focus on the Serine protease 2 (Ser2) gene in the lepidopteran pest Spodoptera litura. The Ser2 gene was specifically expressed in male adults. Disruption of the Ser2 gene mediated by CRISPR/Cas9 induced male sterility but females remained fertile. PCR-based detection of the next-generation mutants showed that male sterility was stably inherited. The qRT-PCR analysis of SlSer2 mutants showed that motor protein family genes and structural protein family genes were down-regulated, while protein modification family genes were up-regulated, suggesting that SlSer2 may be involved in sperm movement and activity. These results demonstrate that Ser2 is an important component of SFPs in seminal fluid and was identified for a useful sterile gene for pest control that may lead to new control strategies for lepidopteran insect pests such as S. litura.

Transcriptome analysis of Holotrichia oblita reveals differentially expressed unigenes related to reproduction and development under different photoperiods

Holotrichia oblita (Faldermann) (Coleoptera: Scarabaeidae) is an insect whose feeding and mating behaviors occur at night. A scotophase is necessary for H. oblita reproduction. We used RNA sequencing (RNA-seq) to compare the expression patterns of H. oblita at five photoperiods (0:24, 8:16, 12:12, 16:8, and 24:0 h) (L:D). Compared to the control (24:0) (L:D), 161-684 differentially expressed unigenes (DEUs) were found in female samples, while 698-2322 DEUs were found in male samples. For all DEUs, a total of 92-1143 DEUs were allocated to 116-662 categories of gene ontology (GO), and 81-1116 DEUs were assigned into 77-286 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The iPath diagram showed that the DEUs generated by comparing female and male samples with photoperiods of 0:24 and 24:0, respectively, involved multiple metabolic pathways, such as carbohydrate metabolism, lipid metabolism, nucleotide metabolism, purine metabolism and glutathione metabolism. Most of these DEUs were upregulated. Finally, 13 DEUs related to reproduction and development were selected to confirm the consistency of relative expression between RNA-Seq and quantitative real-time polymerase chain reaction (qRT-PCR). Most of these comparison results agreed well, except for some qRT-PCR results that were not detected in male samples due to their low expression. These results provide useful information for understanding the dark-induced reproduction of H. oblita.

Putative Degradation of Non-Stored Sperm in the Female Reproductive Tract of the Dengue Vector Mosquito Aedes aegypti

In insect vectors of disease, male and female molecules that mediate reproductive processes are promising targets to suppress fertility of these populations. One process, the storage of sperm in the female reproductive tract, is essential for optimal fertility in all organisms examined to date. In the dengue vector mosquito Aedes aegypti, female sperm storage has not been fully characterized, a requirement to identify sex-specific molecules that mediate this process. Aedes aegypti males deposit the ejaculate into the bursa of the female reproductive tract, and sperm enter the spermathecae—the long-term storage sites—quickly after insemination. However, the proportion of sperm received during mating that are stored in the spermathecae is unclear, and the fate of non-stored sperm unknown. We quantified sperm storage in two Ae. aegypti strains, mated in all combinations, and in two contexts (mass mated and when mating was observed) at 1-, 3- and 5-days post-mating. Sperm quantity in the spermathecae was similar at all timepoints; most females stored ~400 sperm on average. Sperm that did not enter the spermathecae remained in the bursa, where they declined in number and became more fragile to mechanical manipulation at each timepoint. Further, sperm viability in the bursa fell from 91.6% shortly after mating to 12.2% 24 h later. One day after insemination, ~50% of sperm detected in the female reproductive tract was stored in the spermathecae. When we quantified sperm storage in females mated to males that transferred reduced ejaculate quantities (but still able to induce optimal fertility in their mates), sperm detected in the spermathecae similarly declined; females stored ~50% of the sperm received even as sperm quantities transferred at mating declined. Our results suggest that sperm storage in Ae. aegypti females is influenced by ejaculate volume, and that sperm that do not enter the spermathecae remain in the bursa, where they appear to degrade. The consistent presence of sperm in the bursa, even when males transferred low sperm quantities, suggests that the putative degradation of bursa sperm may play a role in Ae. aegypti female fertility, potentially identifying a novel process in this important vector species.

CRISPR/Cas9 Mediated Disruption of Seminal Fluid Protein Sfp62 Induces Male Sterility in Bombyx mori

Simple Summary

In gamogenetic animals, seminal fluid proteins are essential for male fertility. In this study, we investigated the function of the seminal fluid protein Sfp62 by using the CRISPR/Cas9 system in lepidopteran model insect Bombyx mori. Sfp62 mutation led to male sterility and can be inherited stably. The mutation did not affect growth and developmental nor female fertility. These data indicate that Sfp62 is an ideal target for sterile insect technology (SIT), in which genetically modified insects are released on a large scale to mate with wild-type insects in order to reduce or even eradicate the target pests. The determining factors for the effective implementation of SIT include the strong competitiveness of the modified individuals and multi-generational effects resulting from the mutation. Sfp62 meets these criteria and is therefore a promising target for biological pest control.

Abstract

Seminal fluid proteins provide factors necessary for development, storage, and activation of sperm. Altered expression of seminal fluid proteins can lead to defect in male infertility. We investigated the function of seminal fluid protein Sfp62 in the model lepidopteran insect Bombyx mori using CRISPR/Cas9 mediated mutagenesis. The knockout of BmSfp62 gene led to male sterility but has no effect on female fertility. The mutation did not affect growth and development of the silkworm of both sexes. Motility of sperm in male mutants was decreased and the mRNA expression levels of other genes encoding seminal fluid proteins were altered in BmSfp62 mutants compared to the wild-type controls. The male sterility caused by mutation of BmSfp62 was stably inherited. As the proteins encoded by Sfp62 genes are conserved among lepidopteran species, Sfp62 is a potential target for the biological management of lepidopteran pests.

piggyBac-based transgenic RNAi of serine protease 2 results in male sterility in Hyphantria cunea

Fall webworm, Hyphantria cunea, is a global invasive forest pest that causes serious damage to the economy and ecosystem of agriculture and forestry. Due to the extent of the problem and the difficulty of conventional chemical control, new technologies must be pursued, such as genetic-based inheritable insect sterile technology (gSIT), which exhibits promise for pest control. In the present study, we established a piggyBac-based transgenic system in fall webworm and generated a dominant male-sterile strain by targeting the seminal fluid protein serine protease 2 (Hcser2), displaying an outstanding trait of gSIT. First, an RNA polymerase type III (Pol III) promoter, the HcU62 small nuclear RNA (snRNA) gene promoter, was identified and characterized through direct injection of RNAi plasmids in vivo. Quantitative real-time PCR revealed that HcU62 had the greatest knockdown efficiency of the Hcyellow gene among five short hairpin RNA (shRNA) plasmids tested, designated HcU61-HcU65. Second, subsequent application of piggyBac-based transgenic RNAi (HcU62: shHcyellow, Ysh2) significantly reduced the expression level of the Hcyellow gene, resulting in a stable yellow observable phenotype from the larval to pupal stages in Ysh2 transgenic mutants. Finally, an HcU62-driven transgenic RNAi strain targeting the Hcser2 gene was obtained, resulting in a dominant male-sterile phenotype. Significantly, this process did not affect the growth, development, mating behavior or egg laying of the mutants, and the dominant sterile trait could be inherited in the next generation through female Hcser2 mutants. Furthermore, CRISPR/Cas9-mediated disruption of the Hcser2 gene further confirmed the dominant sterile phenotype, supporting it as a generalized target for genetic control of H. cunea. This study reports the first piggyBac-mediated transgenic system in H. cunea, providing a promising genetic method for controlling this pest by targeting Hcser2 gene.

The life history of Drosophila sperm involves molecular continuity between male and female reproductive tracts

In species with internal fertilization, sperm spend an important part of their lives within the female. To examine the life history of the sperm during this time, we used semiquantitative proteomics and sex-specific isotopic labeling in fruit flies to determine the extent of molecular continuity between male and female reproductive tracts and provide a global catalog of sperm-associated proteins. Multiple seminal fluid proteins and female proteins associate with sperm immediately after mating. Few seminal fluid proteins remain after long-term sperm storage, whereas female-derived proteins constitute one-fifth of the postmating sperm proteome by then. Our data reveal a molecular “hand-off” from males to females, which we postulate to be an important component of sperm–female interactions.

Interactions between sperm and the female reproductive tract (FRT) are critical to reproductive success and yet are poorly understood. Because sperm complete their functional maturation within the FRT, the life history of sperm is likely to include a molecular “hand-off” from males to females. Although such intersexual molecular continuity is likely to be widespread among all internally fertilizing species, the identity and extent of female contributions are largely unknown. We combined semiquantitative proteomics with sex-specific isotopic labeling to catalog the posttesticular life history of the sperm proteome and determine the extent of molecular continuity between male and FRTs. We show that the Drosophila melanogaster sperm proteome undergoes substantial compositional changes after being transferred to the FRT. Multiple seminal fluid proteins initially associate with sperm, but most become undetectable after sperm are stored. Female-derived proteins also begin to associate with sperm immediately after mating, and they comprise nearly 20% of the postmating sperm proteome following 4 d of storage in the FRT. Female-derived proteins that associate with sperm are enriched for processes associated with energy metabolism, suggesting that female contributions support sperm viability during the prolonged period between copulation and fertilization. Our research provides a comprehensive characterization of sperm proteome dynamics and expands our understanding of the critical process of sperm–FRT interactions.

Seminal fluid gene expression and reproductive fitness in Drosophila melanogaster

Background

The rapid evolution of seminal fluid proteins (SFPs) has been suggested to be driven by adaptations to postcopulatory sexual selection (e.g. sperm competition). However, we have recently shown that most SFPs evolve rapidly under relaxed selective pressures. Given the role of SFPs in competition for fertilization phenotypes, like the ability to transfer and store sperm and the modulation of female receptivity and ovulation, the prevalence of selectively relaxed SFPs appears as a conundrum. One possible explanation is that selection on SFPs might be relaxed in terms of protein amino acid content, but adjustments of expression are essential for post-mating function. Interestingly, there is a general lack of systematic implementation of gene expression perturbation assays to monitor their effect on phenotypes related to sperm competition.

Results

We successfully manipulated the expression of 16 SFP encoding genes using tissue-specific knockdowns (KDs) and determined the effect of these genes’ perturbation on three important post-mating phenotypes: female refractoriness to remating, defensive (P1), and offensive (P2) sperm competitive abilities in Drosophila melanogaster. Our analyses show that KDs of tested SFP genes do not affect female refractoriness to remating and P2, however, most gene KDs significantly decreased P1. Moreover, KDs of SFP genes that are selectively constrained in terms of protein-coding sequence evolution have lower P1 than KDs of genes evolving under relaxed selection.

Conclusions

Our results suggest a more predominant role, than previously acknowledged, of variation in gene expression than coding sequence changes on sperm competitive ability in D. melanogaster.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-022-01975-1.

Mutation of Serine protease 1 Induces Male Sterility in Bombyx mori

Serine proteases are important in reproduction, embryonic development, cell differentiation, apoptosis, and immunity. The genes encoding some serine proteases are essential for male fertility in both humans and rodents and are functionally conserved among metazoan. For example, the Serine protease 1 (Ser1) gene determines male reproductive success in the model lepidopteran insect Bombyx mori. In this study, we explored the function of BmSer1 through transgenic CRISPR/Cas9 technology-mediated mutations in silkworm. We found that the mutation of BmSer1 gene resulted in male sterility but had no effect on female fertility. Male mutants produce normal eupyrene sperm bundles, but the sperm bundles do not dissociate into single sperm. Male sterility caused by the BmSer1 gene mutation was inherited stably through female individuals. Therefore, the serine protease encoded by BmSer1 is essential for male reproductive success in lepidopterans and is a potential target gene for biological reproductive regulation.

Single-nucleus transcriptomes reveal evolutionary and functional properties of cell types in the Drosophila accessory gland

Many traits responsible for male reproduction evolve quickly, including gene expression phenotypes in germline and somatic male reproductive tissues. Rapid male evolution in polyandrous species is thought to be driven by competition among males for fertilizations and conflicts between male and female fitness interests that manifest in postcopulatory phenotypes. In Drosophila, seminal fluid proteins secreted by three major cell types of the male accessory gland and ejaculatory duct are required for female sperm storage and use, and influence female postcopulatory traits. Recent work has shown that these cell types have overlapping but distinct effects on female postcopulatory biology, yet relatively little is known about their evolutionary properties. Here, we use single-nucleus RNA-Seq of the accessory gland and ejaculatory duct from Drosophila melanogaster and two closely related species to comprehensively describe the cell diversity of these tissues and their transcriptome evolution for the first time. We find that seminal fluid transcripts are strongly partitioned across the major cell types, and expression of many other genes additionally defines each cell type. We also report previously undocumented diversity in main cells. Transcriptome divergence was found to be heterogeneous across cell types and lineages, revealing a complex evolutionary process. Furthermore, protein adaptation varied across cell types, with potential consequences for our understanding of selection on male postcopulatory traits.

Proteolysis in Reproduction: Lessons From Gene-Modified Organism Studies

The physiological roles of proteolysis are not limited to degrading unnecessary proteins. Proteolysis plays pivotal roles in various biological processes through cleaving peptide bonds to activate and inactivate proteins including enzymes, transcription factors, and receptors. As a wide range of cellular processes is regulated by proteolysis, abnormalities or dysregulation of such proteolytic processes therefore often cause diseases. Recent genetic studies have clarified the inclusion of proteases and protease inhibitors in various reproductive processes such as development of gonads, generation and activation of gametes, and physical interaction between gametes in various species including yeast, animals, and plants. Such studies not only clarify proteolysis-related factors but the biological processes regulated by proteolysis for successful reproduction. Here the physiological roles of proteases and proteolysis in reproduction will be reviewed based on findings using gene-modified organisms.

Seminal fluid proteins induce transcriptome changes in the Aedes aegypti female lower reproductive tract

BACKGROUND

Mating induces behavioral and physiological changes in the arbovirus vector Aedes aegypti, including stimulation of egg development and oviposition, increased survival, and reluctance to re-mate with subsequent males. Transferred seminal fluid proteins and peptides derived from the male accessory glands induce these changes, though the mechanism by which they do this is not known.

RESULTS

To determine transcriptome changes induced by seminal proteins, we injected extract from male accessory glands and seminal vesicles (MAG extract) into females and examined female lower reproductive tract (LRT) transcriptomes 24 h later, relative to non-injected controls. MAG extract induced 87 transcript-level changes, 31 of which were also seen in a previous study of the LRT 24 h after a natural mating, including 15 genes with transcript-level changes similarly observed in the spermathecae of mated females. The differentially-regulated genes are involved in diverse molecular processes, including immunity, proteolysis, neuronal function, transcription control, or contain predicted small-molecule binding and transport domains.

CONCLUSIONS

Our results reveal that seminal fluid proteins, specifically, can induce gene expression responses after mating and identify gene targets to further investigate for roles in post-mating responses and potential use in vector control.

Rapid stress hardening in the Antarctic midge improves male fertility by increasing courtship success and preventing decline of accessory gland proteins following cold exposure

Rapid hardening is a process that quickly improves an animal's performance following exposure to potentially damaging stress. In this study of the Antarctic midge, Belgica antarctica (Diptera, Chironomidae), we examined how rapid hardening in response to dehydration (RDH) or cold (RCH) improves male pre- and post-copulatory function when the insects are subsequently subjected to a damaging cold exposure. Neither RDH nor RCH improved survival in response to lethal cold stress, but male activity and mating success following sublethal cold exposure were enhanced. Egg viability decreased following direct exposure of the mating males to sublethal cold but improved following RCH and RDH. Sublethal cold exposure reduced the expression of four accessory gland proteins, while expression remained high in males exposed to RCH. Though rapid hardening may be cryptic in males, this study shows that it can be revealed by pre- and post-copulatory interactions with females.

Nonadaptive molecular evolution of seminal fluid proteins in Drosophila

Seminal fluid proteins (SFPs) are a group of reproductive proteins that are among the most evolutionarily divergent known. As SFPs can impact male and female fitness, these proteins have been proposed to evolve under postcopulatory sexual selection (PCSS). However, the fast change of the SFPs can also result from nonadaptive evolution, and the extent to which selective constraints prevent SFPs rapid evolution remains unknown. Using intra‐ and interspecific sequence information, along with genomics and functional data, we examine the molecular evolution of approximately 300 SFPs in Drosophila. We found that 50–57% of the SFP genes, depending on the population examined, are evolving under relaxed selection. Only 7–12% showed evidence of positive selection, with no evidence supporting other forms of PCSS, and 35–37% of the SFP genes were selectively constrained. Further, despite associations of positive selection with gene location on the X chromosome and protease activity, the analysis of additional genomic and functional features revealed their lack of influence on SFPs evolving under positive selection. Our results highlight a lack of sufficient evidence to claim that most SFPs are driven to evolve rapidly by PCSS while identifying genomic and functional attributes that influence different modes of SFPs evolution.

Gene expression and alternative splicing dynamics are perturbed in female head transcriptomes following heterospecific copulation

BACKGROUND

Despite the growing interest in the female side of copulatory interactions, the roles played by differential expression and alternative splicing mechanisms of pre-RNA on tissues outside of the reproductive tract have remained largely unknown. Here we addressed these questions in the context of con- vs heterospecific matings between Drosophila mojavensis and its sister species, D. arizonae. We analyzed transcriptional responses in female heads using an integrated investigation of genome-wide patterns of gene expression, including differential expression (DE), alternative splicing (AS) and intron retention (IR).

RESULTS

Our results indicated that early transcriptional responses were largely congruent between con- and heterospecific matings but are substantially perturbed over time. Conspecific matings induced functional pathways related to amino acid balance previously associated with the brain's physiology and female postmating behavior. Heterospecific matings often failed to activate regulation of some of these genes and induced expression of additional genes when compared with those of conspecifically-mated females. These mechanisms showed functional specializations with DE genes mostly linked to pathways of proteolysis and nutrient homeostasis, while AS genes were more related to photoreception and muscle assembly pathways. IR seems to play a more general role in DE regulation during the female postmating response.

CONCLUSIONS

We provide evidence showing that AS genes substantially perturbed by heterospecific matings in female heads evolve at slower evolutionary rates than the genome background. However, DE genes evolve at evolutionary rates similar, or even higher, than those of male reproductive genes, which highlights their potential role in sexual selection and the evolution of reproductive barriers.

Differences in Postmating Transcriptional Responses between Conspecific and Heterospecific Matings in Drosophila

In many animal species, females undergo physiological and behavioral changes after mating. Some of these changes are driven by male-derived seminal fluid proteins and are critical for fertilization success. Unfortunately, our understanding of the molecular interplay between female and male reproductive proteins remains inadequate. Here, we analyze the postmating response in a Drosophila species that has evolved strong gametic incompatibility with its sister species; Drosophila novamexicana females produce only ∼1% fertilized eggs in crosses with Drosophila americana males, compared to ∼98% produced in within-species crosses. This incompatibility is likely caused by mismatched male and female reproductive molecules. In this study, we use short-read RNA sequencing to examine the evolutionary dynamics of female reproductive genes and the postmating transcriptome response in crosses within and between species. First, we found that most female reproductive tract genes are slow-evolving compared to the genome average. Second, postmating responses in con- and heterospecific matings are largely congruent, but heterospecific matings induce expression of additional stress-response genes. Some of those are immunity genes that are activated by the Imd pathway. We also identify several genes in the JAK/STAT signaling pathway that are induced in heterospecific, but not conspecific mating. While this immune response was most pronounced in the female reproductive tract, we also detect it in the female head and ovaries. These results show that the female's postmating transcriptome-level response is determined in part by the genotype of the male, and that divergence in male reproductive genes and/or traits can have immunogenic effects on females.

Expression of Mst89B and CG31287 is Needed for Effective Sperm Storage and Egg Fertilization in Drosophila

In Drosophila, male reproductive fitness can be affected by any number of processes, ranging from development of gametes, transfer to and storage of mature sperm within the female sperm storage organs, and utilization of sperm for fertilization. We have previously identified the 89B cytogenetic map position of D. melanogaster as a hub for genes that effect male paternity success when disturbed. Here, we used RNA interference to test 11 genes that are highly expressed in the testes and located within the 89B region for their role in sperm competition and male fecundity when their expression is perturbed. Testes-specific knockdown (KD) of bor and CSN5 resulted in complete sterility, whereas KD of CG31287, Manf and Mst89B, showed a breakdown in sperm competitive success when second to mate (P2 < 0.5) and reduced fecundity in single matings. The low fecundity of Manf KD is explained by a significant reduction in the amount of mature sperm produced. KD of Mst89B and CG31287 does not affect sperm production, sperm transfer into the female bursa or storage within 30 min after mating. Instead, a significant reduction of sperm in female storage is observed 24 h after mating. Egg hatchability 24 h after mating is also drastically reduced for females mated to Mst89B or CG31287 KD males, and this reduction parallels the decrease in fecundity. We show that normal germ-line expression of Mst89B and CG31287 is needed for effective sperm usage and egg fertilization.

PCE3 Plays a Role in the Reproduction of Male Nilaparvata lugens

Simple Summary

The brown planthopper (BPH), Nilaparvata lugens, is one of the most harmful rice crop pest insects. The use of RNAi is a feasible strategy for controlling this pest. In this study, we evaluated the importance of PCE3 in the development and reproduction of male BPH. We found that PCE3 could regulate the development of the male internal genitalia and reduce the oviposition level of the females that mated with males treated with dsRNA targeting the N. lugens PCE3 gene, causing eggs not to hatch. Our findings indicate that PCE3 is an important gene in regulating male fecundity and a promising target for controlling BPH.

Abstract

Nilaparvata lugens proclotting enzymes (NlPCEs) belong to the clip domain serine protease (clip-SP) family, which is a characteristic protease family in arthropods. NlPCE3 was previously reported to regulate egg production and development in female N. lugens, but its role in male N. lugens is unclear. In the present study, qPCR analysis showed that NlPCE3 was expressed in three different tissues (gut, testis and fat body). RNAi revealed that dsNlPCE3 injection made the male vas deferens thinner and reduced the oviposition level of the females that mated with dsNlPCE3-treated males, causing eggs not to hatch. Furthermore, immunofluorescence staining showed that NlPCE3 was widely expressed in the male internal genitalia. However, after dsNlPCE3 injection, expression of NlPCE3 was diffuse in the male internal genitalia, whose peripheral cells seemed degraded. Overall, these results indicate that NlPCE3 is important for reproduction in male N. lugens.

Mating-regulated atrial proteases control reinsemination rates in Anopheles gambiae females

Anopheles gambiae mosquitoes are the most important vectors of human malaria. The reproductive success of these mosquitoes relies on a single copulation event after which the majority of females become permanently refractory to further mating. This refractory behavior is at least partially mediated by the male-synthetized steroid hormone 20-hydroxyecdysone (20E), which is packaged together with other seminal secretions into a gelatinous mating plug and transferred to the female atrium during mating. In this study, we show that two 20E-regulated chymotrypsin-like serine proteases specifically expressed in the reproductive tract of An. gambiae females play an important role in modulating the female susceptibility to mating. Silencing these proteases by RNA interference impairs correct plug processing and slows down the release of the steroid hormone 20E from the mating plug. In turn, depleting one of these proteases, the Mating Regulated Atrial Protease 1 (MatRAP1), reduces female refractoriness to further copulation, so that a significant proportion of females mate again. Microscopy analysis reveals that MatRAP1 is localized on a previously undetected peritrophic matrix-like structure surrounding the mating plug. These data provide novel insight into the molecular mechanisms shaping the post-mating biology of these important malaria vectors.

Mitochondrial-Y chromosome epistasis in Drosophila melanogaster

The coordination between mitochondrial and nuclear genes is crucial to eukaryotic organisms. Predicting the nature of these epistatic interactions can be difficult because of the transmission asymmetry of the genes involved. While autosomes and X-linked genes are transmitted through both sexes, genes on the Y chromosome and in the mitochondrial genome are uniparentally transmitted through males and females, respectively. Here, we generate 36 otherwise isogenic Drosophila melanogaster strains differing only in the geographical origin of their mitochondrial genome and Y chromosome, to experimentally examine the effects of the uniparentally inherited parts of the genome, as well as their interaction, in males. We assay longevity and gene expression through RNA-sequencing. We detect an important role for both mitochondrial and Y-linked genes, as well as extensive mitochondrial-Y chromosome epistasis. In particular, genes involved in male reproduction appear to be especially sensitive to such interactions, and variation on the Y chromosome is associated with differences in longevity. Despite these interactions, we find no evidence that the mitochondrial genome and Y chromosome are co-adapted within a geographical region. Overall, our study demonstrates a key role for the uniparentally inherited parts of the genome for male biology, but also that mito-nuclear interactions are complex and not easily predicted from simple transmission asymmetries.

The Drosophila seminal proteome and its role in postcopulatory sexual selection

Postcopulatory sexual selection (PCSS), comprised of sperm competition and cryptic female choice, has emerged as a widespread evolutionary force among polyandrous animals. There is abundant evidence that PCSS can shape the evolution of sperm. However, sperm are not the whole story: they are accompanied by seminal fluid substances that play many roles, including influencing PCSS. Foremost among seminal fluid models is Drosophila melanogaster, which displays ubiquitous polyandry, and exhibits intraspecific variation in a number of seminal fluid proteins (Sfps) that appear to modulate paternity share. Here, we first consolidate current information on the identities of D. melanogaster Sfps. Comparing between D. melanogaster and human seminal proteomes, we find evidence of similarities between many protein classes and individual proteins, including some D. melanogaster Sfp genes linked to PCSS, suggesting evolutionary conservation of broad-scale functions. We then review experimental evidence for the functions of D. melanogaster Sfps in PCSS and sexual conflict. We identify gaps in our current knowledge and areas for future research, including an enhanced identification of PCSS-related Sfps, their interactions with rival sperm and with females, the role of qualitative changes in Sfps and mechanisms of ejaculate tailoring. This article is part of the theme issue 'Fifty years of sperm competition'.

Chromosome-level de novo genome assembly of Sarcophaga peregrina provides insights into the evolutionary adaptation of flesh flies

Sarcophaga peregrina is considered to be of great ecological, medical and forensic significance, and has unusual biological characteristics such as an ovoviviparous reproductive pattern and adaptation to feed on carrion. The availability of a high-quality genome will help to further reveal the mechanisms underlying these charcateristics. Here we present a de novo-assembled genome at chromosome scale for S. peregrina. The final assembled genome was 560.31 Mb with contig N50 of 3.84 Mb. Hi-C scaffolding reliably anchored six pseudochromosomes, accounting for 97.76% of the assembled genome. Moreover, 45.70% of repeat elements were identified in the genome. A total of 14,476 protein-coding genes were functionally annotated, accounting for 92.14% of all predicted genes. Phylogenetic analysis indicated that S. peregrina and S. bullata diverged ~ 7.14 million years ago. Comparative genomic analysis revealed expanded and positively selected genes related to biological features that aid in clarifying its ovoviviparous reproduction and carrion-feeding adaptations, such as lipid metabolism, olfactory receptor activity, antioxidant enzymes, proteolysis and serine-type endopeptidase activity. Protein-coding genes associated with ovoviparity, such as yolk proteins, transferrin and acid sphingomyelinase, were identified. This study provides a valuable genomic resource for S. peregrina, and sheds insight into further revealing the underlying molecular mechanisms of adaptive evolution.

Male reproductive aging arises via multifaceted mating-dependent sperm and seminal proteome declines, but is postponable in Drosophila

Declining ejaculate performance with male age is taxonomically widespread and has broad fitness consequences. Ejaculate success requires fully functional germline (sperm) and soma (seminal fluid) components. However, some aging theories predict that resources should be preferentially diverted to the germline at the expense of the soma, suggesting differential impacts of aging on sperm and seminal fluid and trade-offs between them or, more broadly, between reproduction and lifespan. While harmful effects of male age on sperm are well known, we do not know how much seminal fluid deteriorates in comparison. Moreover, given the predicted trade-offs, it remains unclear whether systemic lifespan-extending interventions could ameliorate the declining performance of the ejaculate as a whole. Here, we address these problems using Drosophila melanogaster. We demonstrate that seminal fluid deterioration contributes to male reproductive decline via mating-dependent mechanisms that include posttranslational modifications to seminal proteins and altered seminal proteome composition and transfer. Additionally, we find that sperm production declines chronologically with age, invariant to mating activity such that older multiply mated males become infertile principally via reduced sperm transfer and viability. Our data, therefore, support the idea that both germline and soma components of the ejaculate contribute to male reproductive aging but reveal a mismatch in their aging patterns. Our data do not generally support the idea that the germline is prioritized over soma, at least, within the ejaculate. Moreover, we find that lifespan-extending systemic down-regulation of insulin signaling results in improved late-life ejaculate performance, indicating simultaneous amelioration of both somatic and reproductive aging.

Drosophila seminal sex peptide associates with rival as well as own sperm, providing SP function in polyandrous females

When females mate with more than one male, the males’ paternity share is affected by biases in sperm use. These competitive interactions occur while female and male molecules and cells work interdependently to optimize fertility, including modifying the female’s physiology through interactions with male seminal fluid proteins (SFPs). Some modifications persist, indirectly benefiting later males. Indeed, rival males tailor their ejaculates accordingly. Here, we show that SFPs from one male can directly benefit a rival’s sperm. We report that Sex Peptide (SP) that a female Drosophila receives from a male can bind sperm that she had stored from a previous male, and rescue the sperm utilization and fertility defects of an SP-deficient first-male. Other seminal proteins received in the first mating ‘primed’ the sperm (or the female) for this binding. Thus, SP from one male can directly benefit another, making SP a key molecule in inter-ejaculate interaction.

When fruit flies and other animals reproduce, a compatible male and a female mate, allowing sperm from the male to swim to and fuse with the female’s egg cells. The males also produce proteins known as seminal proteins that travel with the sperm. These proteins increase the likelihood of sperm meeting an egg and induce changes in the female that increase the number, or quality, of offspring produced.

Some seminal proteins help a male to compete against its rivals by decreasing their chances to fertilize eggs. However, since many of the changes seminal proteins induce in females are long-lasting, it is possible that a subsequent male may actually benefit indirectly from the effects of a prior male’s seminal proteins. It remains unclear whether the seminal proteins of one male are also able to directly interact with and help the sperm of another male.

Male fruit flies make a seminal protein known as sex peptide. Normally, a sex peptide binds to the sperm it accompanies into the female, increasing the female’s fertility and preventing her from mating again with a different male. To test whether the sex peptide from one male can bind to and help a rival male’s sperm, Misra and Wolfner mated female fruit flies with different combinations of males that did, or did not, produce the sex peptide.

The experiments found that female flies that only mated with mutant males lacking the sex peptide produced fewer offspring than if they had mated with a ‘normal’ male. However, in females that mated with a mutant male followed by another male who provided the sex peptide, the second male’s sex peptide was able to bind to the mutant male’s sperm (as well as to his own). This in turn allowed the mutant male’s sperm to be efficiently used to sire offspring, at levels comparable to a normal male providing the sex peptide.

These findings demonstrate that the ways individual male fruit flies interact during reproduction are more complex than just simple rivalry. Since humans and other animals also produce seminal proteins comparable to those of fruit flies, this work may aid future advances in human fertility treatments and strategies to control the fertility of livestock and pests, including mosquitoes that transmit diseases.

Quantitative proteomics reveals rapid divergence in the postmating response of female reproductive tracts among sibling species

Fertility depends, in part, on interactions between male and female reproductive proteins inside the female reproductive tract (FRT) that mediate postmating changes in female behaviour, morphology, and physiology. Coevolution between interacting proteins within species may drive reproductive incompatibilities between species, yet the mechanisms underlying postmating-prezygotic (PMPZ) isolating barriers remain poorly resolved. Here, we used quantitative proteomics in sibling Drosophila species to investigate the molecular composition of the FRT environment and its role in mediating species-specific postmating responses. We found that (i) FRT proteomes in D. simulans and D. mauritiana virgin females express unique combinations of secreted proteins and are enriched for distinct functional categories, (ii) mating induces substantial changes to the FRT proteome in D. mauritiana but not in D. simulans, and (iii) the D. simulans FRT proteome exhibits limited postmating changes irrespective of whether females mate with conspecific or heterospecific males, suggesting an active female role in mediating reproductive interactions. Comparisons with similar data in the closely related outgroup species D. melanogaster suggest that divergence is concentrated on the D. simulans lineage. Our study suggests that divergence in the FRT extracellular environment and postmating response contribute to previously described patterns of PMPZ isolation and the maintenance of species boundaries.

Post-ejaculatory modifications to sperm (PEMS)

Mammalian sperm must spend a minimum period of time within a female reproductive tract to achieve the capacity to fertilize oocytes. This phenomenon, termed sperm 'capacitation', was discovered nearly seven decades ago and opened a window into the complexities of sperm-female interaction. Capacitation is most commonly used to refer to a specific combination of processes that are believed to be widespread in mammals and includes modifications to the sperm plasma membrane, elevation of intracellular cyclic AMP levels, induction of protein tyrosine phosphorylation, increased intracellular Ca2+ levels, hyperactivation of motility, and, eventually, the acrosome reaction. Capacitation is only one example of post-ejaculatory modifications to sperm (PEMS) that are widespread throughout the animal kingdom. Although PEMS are less well studied in non-mammalian taxa, they likely represent the rule rather than the exception in species with internal fertilization. These PEMS are diverse in form and collectively represent the outcome of selection fashioning complex maturational trajectories of sperm that include multiple, sequential phenotypes that are specialized for stage-specific functionality within the female. In many cases, PEMS are critical for sperm to migrate successfully through the female reproductive tract, survive a protracted period of storage, reach the site of fertilization and/or achieve the capacity to fertilize eggs. We predict that PEMS will exhibit widespread phenotypic plasticity mediated by sperm-female interactions. The successful execution of PEMS thus has important implications for variation in fitness and the operation of post-copulatory sexual selection. Furthermore, it may provide a widespread mechanism of reproductive isolation and the maintenance of species boundaries. Despite their possible ubiquity and importance, the investigation of PEMS has been largely descriptive, lacking any phylogenetic consideration with regard to divergence, and there have been no theoretical or empirical investigations of their evolutionary significance. Here, we (i) clarify PEMS-related nomenclature; (ii) address the evolutionary origin, maintenance and divergence in PEMS in the context of the protracted life history of sperm and the complex, selective environment of the female reproductive tract; (iii) describe taxonomically widespread types of PEMS: sperm activation, chemotaxis and the dissociation of sperm conjugates; (iv) review the occurence of PEMS throughout the animal kingdom; (v) consider alternative hypotheses for the adaptive value of PEMS; (vi) speculate on the evolutionary implications of PEMS for genomic architecture, sexual selection, and reproductive isolation; and (vii) suggest fruitful directions for future functional and evolutionary analyses of PEMS.

Molecular evolution of the sex peptide network in Drosophila

Successful reproduction depends on interactions between numerous proteins beyond those involved directly in gamete fusion. Although such reproductive proteins evolve in response to sexual selection pressures, how networks of interacting proteins arise and evolve as reproductive phenotypes change remains an open question. Here, we investigated the molecular evolution of the 'sex peptide network' of Drosophila melanogaster, a functionally well-characterized reproductive protein network. In this species, the peptide hormone sex peptide (SP) and its interacting proteins cause major changes in female physiology and behaviour after mating. In contrast, females of more distantly related Drosophila species do not respond to SP. In spite of these phenotypic differences, we detected orthologs of all network proteins across 22 diverse Drosophila species and found evidence that most orthologs likely function in reproduction throughout the genus. Within SP-responsive species, we detected the recurrent, adaptive evolution of several network proteins, consistent with sexual selection acting to continually refine network function. We also found some evidence for adaptive evolution of several proteins along two specific phylogenetic lineages that correspond with increased expression of the SP receptor in female reproductive tracts or increased sperm length, respectively. Finally, we used gene expression profiling to examine the likely degree of functional conservation of the paralogs of an SP network protein that arose via gene duplication. Our results suggest a dynamic history for the SP network in which network members arose before the onset of robust SP-mediated responses and then were shaped by both purifying and positive selection.

Mutation of the seminal protease gene, serine protease 2, results in male sterility in diverse lepidopterans

Sterile insect technology (SIT) is an environmentally friendly method for pest control. As part of our efforts to develop a strategy that results in engineered male-sterile strains with minimum effects on viability and mating competition, we used CRISPR/Cas9 technology to disrupt Ser2, which encodes a seminal fluid protein, in the model lepidopteran insect, Bombyx mori, and an important agricultural pest, Plutella xylostella. Disruption of Ser2 resulted in dominant heritable male sterility. Wild-type females mated with Ser2-deficient males laid eggs normally, but the eggs did not hatch. We detected no differences in other reproductive behaviors in the mutant males. These results support the conclusion that Ser2 gene is necessary for male reproductive success in diverse lepidopterans. Targeting Ser2 gene has the potential to form the basis for a new strategy for pest control.

Seminal fluid-mediated fitness effects in the simultaneously hermaphroditic flatworm Macrostomum lignano

As a class, seminal fluid proteins are expected to exert strong effects on mating partners due to the selection pressures of sperm competition and sexual conflict. But because of the complexity of this secretion, linking specific proteins to downstream effects on own fitness-via manipulating the reproductive behavior, physiology, and ultimately the sperm utilization of mating partners-is not straightforward. Here, we adopted a systematic gene knockdown approach to screen for seminal fluid-mediated fitness effects in the simultaneously hermaphroditic flatworm Macrostomum lignano. We focused on 18 transcripts in M. lignano seminal fluid, testing how their RNA interference-induced knockdown impacted on three aspects of donor (male) reproductive success: (a) fertility (offspring production of the partner); (b) defensive sperm competitive ability, P 1; and (c) offensive sperm competitive ability, P 2. In general, the knockdown of most individual transcripts appeared to have only a minor impact on male reproductive success, though we found evidence that the knockdown of up to five different transcripts impacted on fertility; the knockdown of two other transcripts resulted in reduced P 2; and knockdown of a further transcript actually increased P 2. We thus identify a number of candidate seminal fluid transcripts that appear to modulate offspring production and sperm competitiveness in M. lignano. That only a minority of transcripts exhibit such a pattern likely reflects both the difficulty of accurately estimating sperm competitiveness and the functional redundancy of seminal fluid.