Molecular evolutionary analysis of seminal receptacle sperm storage organ genes of Drosophila melanogaster

Sperm storage organs are common and broadly distributed among animal taxa. However, little is known about how these organs function at the molecular level. Additionally, there is a paucity of knowledge about the evolution of genes expressed in these organs. This investigation is an evolutionary expressed sequence tag (EST) study of genes expressed in the seminal receptacle, one of the sperm storage organs in Drosophila. The incidence of positive selection is higher for the seminal receptacle genes than Drosophila reproductive genes as a whole, but lower than genes associated with the spermatheca, a second type of Drosophila sperm storage organ. By identifying overrepresented classes of proteins and classes for which sperm storage function is suggested by the nature of the proteins, candidate genes were discovered. These candidates belong to protein classes such as muscle contraction, odorant binding and odorant receptor, protease inhibitor and immunity.     

Human testis-specific genes are under relaxed negative selection

Recent studies have suggested that selective forces and constraints acting on genes varied during human evolution depending on the organ in which they are expressed. To gain insight into the evolution of organ determined negative selection forces, we compared the non-synonymous SNP diversity of genes expressed in different organs. Based on a HAPMAP dataset, we determined for each SNP its frequency in 11 human populations and, in each case, predicted whether or not the change it produces is deleterious. We have shown that, for all organs under study, SNPs predicted to be deleterious are present at a significantly lower frequency than SNPs predicted to be tolerated. However, testis-specific genes contain a higher proportion of deleterious SNPs than other organs. This study shows that negative selection is acting on the whole human genome, but that the action of negative selection is relaxed on testis-specific genes. This result adds to and expands the hypothesis of a recent evolutionary change in the human male reproductive system and its behavior.     

Rates of Evolution of Hominoid Seminal Proteins are Correlated with Function and Expression, Rather than Mating System

In species where females mate with multiple males during a single ovulatory cycle, sperm competition is hypothesized to increase the rate of adaptive evolution of proteins expressed in male reproductive tissues through recurrent selective sweeps (positive selection). The hominoids, comprising apes and humans, are a group of closely related primates with extensive variation in mating behaviors and predicted levels of sperm competition. Since previous studies of individual male reproductive genes have shown evidence of positive selection, we estimated rates of evolution of a comprehensive set of proteins expressed in ejaculated semen. Our results show that these proteins in hominoids do not have elevated rates of nonsynonymous substitutions (Ka) compared with a control dataset of nonreproductive genes. Species with greater sperm competition do not have faster rates of seminal protein evolution. Although at these broad levels our hypotheses were not confirmed, further analyses indicate specific patterns of molecular evolution. Namely, the Ka of seminal genes is more strongly correlated with measures of tissue specificity than nonreproductive genes, suggesting that the former may more readily adapt to tissue-specific functions. Proteins expressed from the seminal vesicles evolve more rapidly than those from other male reproductive tissues. Also, several gene ontology categories show elevated rates of protein evolution, not seen in the control data set. While the generalization that male reproductive genes evolve rapidly in hominoids is an oversimplification, a subset of proteins can be identified that are likely targets for adaptive evolution driven by sexual selection.     

A novel MADS-box gene subfamily with a sister-group relationship to class B floral homeotic genes

Class B floral homeotic genes specify the identity of petals and stamens during the development of angiosperm flowers. Recently, putative orthologs of these genes have been identified in different gymnosperms. Together, these genes constitute a clade, termed B genes. Here we report that diverse seed plants also contain members of a hitherto unknown sister clade of the B genes, termed B(sister) (B(s)) genes. We have isolated members of the B(s) clade from the gymnosperm Gnetum gnemon, the monocotyledonous angiosperm Zea mays and the eudicots Arabidopsis thaliana and Antirrhinum majus. In addition, MADS-box genes from the basal angiosperm Asarum europaeum and the eudicot Petunia hybrida were identified as B(s) genes. Comprehensive expression studies revealed that B(s) genes are mainly transcribed in female reproductive organs (ovules and carpel walls). This is in clear contrast to the B genes, which are predominantly expressed in male reproductive organs (and in angiosperm petals). Our data suggest that the B(s) genes played an important role during the evolution of the reproductive structures in seed plants. The establishment of distinct B and B(s) gene lineages after duplication of an ancestral gene may have accompanied the evolution of male microsporophylls and female megasporophylls 400-300 million years ago. During flower evolution, expression of B(s) genes diversified, but the focus of expression remained in female reproductive organs. Our findings imply that a clade of highly conserved close relatives of class B floral homeotic genes has been completely overlooked until recently and awaits further evaluation of its developmental and evolutionary importance. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00438-001-0615-8.     

Members of the Toll-like receptor family of innate immunity pattern-recognition receptors are abundant in the male rat reproductive tract

Protecting developing and maturing spermatozoa and reproductive tissues from microbial damage is an emerging aspect of research in reproductive physiology. Bacterial, viral, and yeast infections of the testis and epididymis can hinder maturation and movement of spermatozoa, resulting in impaired fertility. Toll-like receptors (TLRs) are a broad family of innate immunity receptors that play critical roles in detecting and responding to invading pathogens. Objectives of this study were to determine if organs of the rat male reproductive tract express mRNAs for members of the TLR family, to characterize expression patterns for TLRs in different regions of the epididymis, and to determine if TLR adaptor and target proteins are present in the male reproductive tract. Messenger RNA for Tlr1-Tlr9 was abundantly expressed in testis, epididymis, and vas deferens, as determined by RT-PCR, while Tlr10 and Tlr11 were less abundantly expressed. Tlr mRNA expression showed no region-specific patterns in the epididymis. Immunoblot analysis revealed relatively equal levels of protein for TLRs 1, 2, 4, and 6 in testis, all regions of the epididymis and vas deferens, and lower levels of TLRs 3, 5, and 9-11. TLR7 was primarily detected in the testis. The TLR adapter proteins, myeloid differentiation primary response gene 88 and TLR adaptor molecule 1, as well as v-rel reticuloendotheliosis viral oncogene homolog and NFKBIA, were prominent in testis, epididymis, and vas deferens. The abundant expression of a majority of TLR family members together with expression of TLR adaptors and activation targets provides strong evidence that TLRs play important roles in innate immunity of the male reproductive tract.     

Genome-wide analysis reveals widespread roles for RcREM genes in floral organ development in Rosa chinensis

Members of the REM (Reproductive Meristem) gene family are expressed primarily in reproductive meristems and floral organs. However, their evolution and their functional profiles in flower development remain poorly understood. Here, we performed genome-wide identification and evolutionary analysis of the REM gene family in Rosaceae. This family has been greatly expanded in rose (Rosa chinensis) compared to other species, primarily through tandem duplication. Expression analysis revealed that most RcREM genes are specifically expressed in reproductive organs and that their specific expression patterns are dramatically altered in rose plants with mutations affecting floral organs. Protein-protein interaction analysis indicated that RcREM14 interact with RcAP1 (one of the homology of A class genes in ABCDE model), highlighting the roles of RcREM genes in floral organ identity. Finally, co-expression network analysis indicated that RcREM genes are co-expressed with a high proportion of key genes that regulate flowering time, floral organ development, and cell proliferation and expansion in R. chinensis.     

Molecular evolution and population genetic analysis of candidate female reproductive genes in Drosophila

Molecular analyses in several taxa have consistently shown that genes involved in reproduction are rapidly evolving and subjected to positive selection. The mechanism behind this evolution is not clear, but several proposed hypotheses involve the coevolution between males and females. In Drosophila, several male reproductive proteins (Acps) involved in male-male and male-female interactions show evidence of rapid adaptive evolution. What has been missing from the Drosophila literature is the identification and analysis of female reproductive genes. Recently, an evolutionary expressed sequence tag analysis of Drosophila female reproductive tract genes identified 169 candidate female reproductive genes. Many of these candidate genes still await further molecular analysis and independent verification of positive selection. Our goal was to expand our understanding of the molecular evolution of Drosophila female reproductive genes with a detailed polymorphism and divergence study on seven additional candidate female reproductive genes and a reanalysis of two genes from the above study. We demonstrate that 6 candidate female genes of the 9 genes surveyed show evidence of positive selection using both polymorphism and divergence data. One of these proteins (CG17012) is modeled to reveal that the sites under selection fall around and within the active site of this protease, suggesting potential differences between species. We discuss our results in light of potential function as well as interaction with male reproductive proteins.     

Expression of cysteine sulfinate decarboxylase (CSD) in male reproductive organs of mice

Cysteine sulfinate decarboxylase (CSD) is the rate-limiting biosynthetic enzyme of taurine, but it is still controversial whether the male reproductive organs have the function to synthesize taurine through CSD pathway. The present study was thus undertaken to detect CSD expression in male mouse reproductive organs by RT-PCR, Western blot and immunohistochemistry. The results show that CSD is expressed both at the mRNA and protein levels in the testis, epididymis and ductus deferens. The relative levels of both CSD mRNA and protein increase from the testis to the epididymis and to the ductus deferens. Immunohistochemical results demonstrate that the main cell types containing CSD are Leydig cells of testis, epithelial cells and some stromal cells throughout the efferent ducts, epididymis and ductus deferens. These results suggest that male genital organs have the function to produce taurine through the CSD pathway, although quantifying the relation of CSD expression to taurine synthesis and the exact functions of taurine in male genital organs still need to be elucidated in future studies.     

Selection analysis on the rapid evolution of a secondary sexual trait

Evolutionary analyses of population translocations (experimental or accidental) have been important in demonstrating speed of evolution because they subject organisms to abrupt environmental changes that create an episode of selection. However, the strength of selection in such studies is rarely measured, limiting our understanding of the evolutionary process. This contrasts with long-term, mark–recapture studies of unmanipulated populations that measure selection directly, yet rarely reveal evolutionary change. Here, we present a study of experimental evolution of male colour in Trinidadian guppies where we tracked both evolutionary change and individual-based measures of selection. Guppies were translocated from a predator-rich to a low-predation environment within the same stream system. We used a combination of common garden experiments and monthly sampling of individuals to measure the phenotypic and genetic divergence of male coloration between ancestral and derived fish. Results show rapid evolutionary increases in orange coloration in both populations (1 year or three generations), replicating the results of previous studies. Unlike previous studies, we linked this evolution to an individual-based analysis of selection. By quantifying individual reproductive success and survival, we show, for the first time, that males with more orange and black pigment have higher reproductive success, but males with more black pigment also have higher risk of mortality. The net effect of selection is thus an advantage of orange but not black coloration, as reflected in the evolutionary response. This highlights the importance of considering all components of fitness when understanding the evolution of sexually selected traits in the wild.     

No intra-locus sexual conflict over reproductive fitness or ageing in field crickets

Differences in the ways in which males and females maximize evolutionary fitness can lead to intra-locus sexual conflict in which genes delivering fitness benefits to one sex are costly when expressed in the other. Trade-offs between current reproductive effort and future reproduction and survival are fundamental to the evolutionary biology of ageing. This leads to the prediction that sex differences in the optimization of age-dependent reproductive effort may generate intra-locus sexual conflict over ageing rates. Here we test for intra-locus sexual conflict over age-dependent reproductive effort and longevity in the black field cricket, Teleogryllus commodus. Using a half-sib breeding design, we show that the most important components of male and female reproductive effort (male calling effort and the number of eggs laid by females) were positively genetically correlated, especially in early adulthood. However, the genetic relationships between longevity and reproductive effort were different for males and females, leading to low genetic covariation between male and female longevity. The apparent absence of intra-locus sexual conflict over ageing suggests that male and female longevity can evolve largely independently of one another.