Complement and complement regulators in the male reproductive system

The multiverse of CD46 and oncologic interactions

Initially identified as a regulator of complement activation on host cells, the known roles of CD46 (membrane cofactor protein [MCP]) have expanded. We now know that this ancient molecule is expressed on almost all nucleated cells as a family of four predominant isoforms. It also is involved in human reproduction, modulation of T cell activation and immunoinflammatory effector functions, autophagy, and the newly identified intracellular complement system (complosome). CD46 is also known as a "pathogen" magnet, being a port of entry for at least seven bacteria and five viruses. Moreover, CD46 has recently emerged as a key player in cancer biology. Numerous studies provide evidence of the association among elevated CD46 expression, malignant transformation, and metastasizing potential. These features, along with its roles as pathogen receptor, have made CD46 a target for cancer therapeutics. Thus, modified viral vectors (such as strains of adenovirus and measles virus) targeting CD46 currently are being exploited against a wide range of cancers. Another oncologic treatment utilizes a CD46-targeting human mAb as an antibody-drug conjugate. Herein, we review CD46 and its "multiverse" of cancer interactions.

Complement regulators as novel targets for anti-cancer therapy: A comprehensive review

Cancer remains a formidable global health challenge requiring the continued exploration of innovative therapeutic approaches. While traditional treatment strategies including surgery, chemotherapy, and radiation therapy have had some success, primarily in early-stage disease, the quest for more targeted, personalized, safer, and effective therapies remains an ongoing pursuit. Over the past decade, significant advances in the field of tumor immunology have dramatically shifted a focus towards immunotherapy, although the ability to harness and coopt the immune system to treat cancer is still just beginning to be realized. One important area that has yet to be fully explored is the complement system, an integral part of innate immunity that has gathered attention recently as a source of potential targets for anti-cancer therapy. The complement system has a complex and context dependent role in cancer biology in that it not only contributes to immune surveillance but also may promote tumor progression. Complement regulators, including CD46, CD55, CD59, and complement factor H, exercise defined control over complement activation, and have also been acknowledged for their role in the tumor microenvironment. This review explores the intricate role of complement regulators in cancer development and progression, examining their potential as therapeutic targets, current strategies, challenges, and the evolving landscape of clinical research.

Chronic inflammation drives epididymal tertiary lymphoid structure formation and autoimmune fertility disorders

The incomplete understanding of epididymal mucosal immunity is a significant contributing factor to the classification of many male infertility cases as idiopathic. Conditions that disrupt the immune balance in the male reproductive tract, such as vasectomy and infections, can expose sperm to the immune system, leading to increased production of anti-sperm antibodies (ASAs) and subsequent reproductive challenges. Regulatory T cells (Tregs) regulate inflammation and maintain sperm tolerance. In a murine model, we demonstrated that disrupting sperm immunotolerance induces chronic autoimmune responses characterized by antibody production targeting sperm and reproductive tissue autoantigens and unique tissue-specific immune cell signatures in the epididymis and testis. Such inflammatory features impair sperm function, contribute to epididymal damage, and drive sustained male subfertility. Tertiary lymphoid structures (TLSs) were formed within the epididymis after Treg depletion, defined by clusters of heterogenous B and T cells, fibroblasts, and endothelial cells. These ectopic structures perpetuate inflammation and lower the activation threshold for future immune threats. Similar isotypes of autoantibodies were detected in the seminal plasma of infertile patients, suggesting shared mechanistic pathways between mice and humans. Overall, we provide an in-depth understanding of the diverse B- and T-cell dynamics and TLS formation during epididymitis to develop precision-targeted therapies for infertility and chronic inflammation. Additionally, this immunological characterization of the epididymal microenvironment has the potential to identify novel targets for the development of male contraceptives.

One Sentence Summary

Understanding the epididymal immune cell landscape dynamics aids in developing targeted therapies for infertility and contraception.

The role of S-palmitoylation of C4BPA in regulating murine sperm motility and complement resistance

The epididymis and epididymosomes are crucial for regulating sperm motility, a key factor in male fertility. Palmitoylation, a lipid modification involving the attachment of palmitic acid to cysteine residues, is essential for protein function and localization. Additionally, this modification plays a vital role in the sorting of proteins into exosomes. This study investigates the role of S-palmitoylation at the Cys15 residue of the C4b binding protein alpha chain (C4BPA) in murine sperm motility. Our findings revealed high expression of C4BPA mRNA in the caput epididymis, with the protein present across all regions of the epididymis. Palmitoylation of C4BPA in epididymal epithelial cells was essential for its enrichment in epididymosomes and on sperm, thereby maintaining sperm motility. Inhibition of palmitoylation significantly reduced sperm motility and the localization of C4BPA on sperm. Additionally, palmitoylated C4BPA in exosomes resisted complement C4 attacks, preserving motility, unlike mutated C4BPA (C15S). These results highlight the critical role of palmitoylated C4BPA in protecting sperm from complement attacks and maintaining motility, suggesting that reversible palmitoylation of epididymal proteins could be explored as a therapeutic strategy for male contraception. Our study underscores the importance of post-translational modifications in sperm function and presents new insights into potential male contraceptive methods.

Relationship among seminal antigenicity, antioxidant status and metabolically active sperm from Holstein-Friesian (Bos taurus) bulls

Sperm antigenicity has been implicated as a regulatory factor for acquiring fertilizing competence in the female reproductive tract. Overt immune response against the sperm proteins leads to idiopathic infertility. Hence, the aim of the study was to evaluate the influence of the auto-antigenic potential of sperm on the antioxidant status, metabolic activities and reactive oxygen species (ROS) in bovine. Semen from Holstein-Friesian bulls (n = 15) was collected and classified into higher (HA, n = 8) and lower (LA, n = 7) antigenic groups based on micro-titer agglutination assay. The neat semen was subjected to the evaluation of bacterial load, leukocyte count, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and lipid peroxidation (LPO) levels. Antioxidant activities in seminal plasma and intracellular ROS levels in the post-thawed sperm were estimated. The number of leukocytes was lower (p < .05) in the HA than the LA semen. The percentage of metabolically active sperm was higher (p < .05) in HA than the LA group. The activities of total non-enzymatic antioxidant, superoxide dismutase (SOD) and catalase (CAT) were higher (p < .05) while glutathione peroxidase activity was lower (p < .05) in the seminal plasma of LA group. The LPO levels of neat sperm and the percentage sperm positive for intracellular ROS in the cryopreserved sample were lower (p < .05) in the HA group. Auto-antigenic levels were positively correlated with the percentage of metabolically active sperm (r = 0.73, p < .01). However, the seminal auto-antigenicity was negatively (p < .05) correlated with the levels of SOD (r=-0.66), CAT (r=-0.72), LPO (r=-0.602) and intracellular ROS (r=-0.835). The findings were represented in graphical abstract. It is inferred that the higher auto-antigenic levels protect the quality of bovine semen by promoting sperm metabolism and lowering ROS and LPO levels.

Proteomic Analysis of Testicular Interstitial Fluid in Men with Azoospermia

Background

The primary microenvironment of the testis comprises testicular interstitial fluid (TIF) surrounding the seminiferous tubules and testicular interstitial tissue. The pathological alterations of germ and Sertoli cells could affect the TIF composition and might contain putative biomarkers for monitoring active spermatogenesis.

Objective

We identified differentially expressed proteins in the TIF of patients with obstructive (OA) or nonobstructive (NOA) azoospermia to elucidate the underlying etiology of defective spermatogenesis.

Design setting and participants

We prospectively enrolled nine patients, including three men with OA and six with NOA with (n = 3) and without (n = 3) successful sperm retrieval. Their TIF was collected during the testicular sperm extraction procedure.

Outcome measurements and statistical analysis

TIF was analyzed using liquid chromatography-tandem mass spectrometry to identify differentially expressed proteins specific to OA and NOA with or without successful sperm retrieval. The dysregulated protein was further validated using Western blotting.

Results and limitations

Among the 555 TIF proteins identified in NOA patients, 14 were downregulated relative to OA patients. These proteins participate in biological processes such as proteolysis, complement activation, and immune responses; complement and coagulation cascade pathways were also enriched. Furthermore, 68 proteins with significantly higher levels were identified in the TIF of NOA patients with successful sperm retrieval than in those with failed sperm retrieval; these are mainly implicated in oxidation-reduction processes. The expression of calreticulin, which can distinguish successful and failed testicular sperm retrieval in the NOA group, was validated by Western blotting.

Conclusions

We provide the first scientific evaluation of TIF protein composition in men with azoospermia. These findings will help identify the physiological and pathological roles of each protein in regulating sperm production. Thus, our study underscores the potential of TIF in sperm retrieval biomarker discovery and would serve as a foundation for further studies to improve treatment strategies against azoospermia.

Patient summary

Using a proteomic approach, we identified and analyzed the total protein content of testicular interstitial fluid in humans with defective spermatogenesis for the first time and discovered altered protein expression patterns in patients with nonobstructive azoospermia (NOA). Proteins related to oxidation-reduction processes were upregulated in NOA patients with successful sperm retrieval compared with those with failed sperm retrieval. This can aid the development of novel diagnostic tools for successful testicular sperm retrieval.

Seminal plasma Alters surface Glycoprofile of dromedary camel cryopreserved epididymal spermatozoa

The high viscosity of Camelidae semen continues to present a major impediment for its application in assisted reproduction technology. The exposure of epididymal spermatozoa (ES) to seminal plasma (SP) may provide an approach to enhance the development of assisted reproductive techniques in these important domestic species. Since the sperm glycocalyx plays a key role in reproduction we aimed to evaluate whether SP exposure modifies the surface glycosylation patterns of cryopreserved dromedary ES. Epididymal sperm was collected through retrograde flushing of the cauda epididymidis that were obtained from orchidectomized mature dromedary bulls. The collected samples were then cryopreserved after dilution with a tris citrate clarified egg yolk extender, with and without the supplementation of 15% SP. Post-thaw carbohydrate surface profiles of both control and SP-treated spermatozoa were analyzed using 15 fluorescent lectins. Morpho-functional properties were also investigated via computer assisted sperm analysis. Lectin-binding analysis of the glycocalyx in control sperm revealed the presence of (1) N-glycans terminating with lactosamine (Con A, PHA-L, and RCA₁₂₀), in both acrosomal and tail regions. Whilst (2) α2,3-/α2,6-linked sialic acids (MALII, SNA), and O-linked glycans terminating with a single N-acetylgalactosamine residue (Tn antigen) (HPA, SBA) along with galactoseβ1,3N-acetylgalactosamine (T antigen) (PNA) were observed in the acrosomal cap. The expression of both N-acetylglucosamine (sWGA and GSA II) and terminalαgalactose (GSA I-B₄) residues was also noted in the acrosomal cap region of control sperm. Compared with controls, SP treated samples displayed: 1) the appearance of bisected di-triantennary complex-type N-glycans (PHA-E), terminating with lactosamine, as well as an increase of O-glycans terminating with Tn and T antigens in both the acrosomal and tail regions; 2) an increase in glycans containing α2,6-linked sialic acid, N-acetylglucosamine, and αgalactose in the tail region. The cytoplasmic droplets of both control and seminal plasma-treated sperm bound Con A, PHA-E, PHA-L, RCA₁₂₀, HPA, PNA, sWGA, GSA I-B₄, and GSA II. These results indicate that SP treatment affects the glycan composition of the dromedary camel ES glycocalyx. More comprehensive studies are required in order to evaluate the fertilization capacity of SP-treated ES in order to facilitate its application in dromedary camel assisted reproduction technology.

Soluble Membrane Attack Complex: Biochemistry and Immunobiology

The soluble membrane attack complex (sMAC, a.k.a., sC5b-9 or TCC) is generated on activation of complement and contains the complement proteins C5b, C6, C7, C8, C9 together with the regulatory proteins clusterin and/or vitronectin. sMAC is a member of the MACPF/cholesterol-dependent-cytolysin superfamily of pore-forming molecules that insert into lipid bilayers and disrupt cellular integrity and function. sMAC is a unique complement activation macromolecule as it is comprised of several different subunits. To date no complement-mediated function has been identified for sMAC. sMAC is present in blood and other body fluids under homeostatic conditions and there is abundant evidence documenting changes in sMAC levels during infection, autoimmune disease and trauma. Despite decades of scientific interest in sMAC, the mechanisms regulating its formation in healthy individuals and its biological functions in both health and disease remain poorly understood. Here, we review the structural differences between sMAC and its membrane counterpart, MAC, and examine sMAC immunobiology with respect to its presence in body fluids in health and disease. Finally, we discuss the diagnostic potential of sMAC for diagnostic and prognostic applications and potential utility as a companion diagnostic.

Molecular Diversification of the Seminal Fluid Proteome in a Recently Diverged Passerine Species Pair

Seminal fluid proteins (SFPs) mediate an array of postmating reproductive processes that influence fertilization and fertility. As such, it is widely held that SFPs may contribute to postmating, prezygotic reproductive barriers between closely related taxa. We investigated seminal fluid (SF) diversification in a recently diverged passerine species pair (Passer domesticus and Passer hispaniolensis) using a combination of proteomic and comparative evolutionary genomic approaches. First, we characterized and compared the SF proteome of the two species, revealing consistencies with known aspects of SFP biology and function in other taxa, including the presence and diversification of proteins involved in immunity and sperm maturation. Second, using whole-genome resequencing data, we assessed patterns of genomic differentiation between house and Spanish sparrows. These analyses detected divergent selection on immunity-related SF genes and positive selective sweeps in regions containing a number of SF genes that also exhibited protein abundance diversification between species. Finally, we analyzed the molecular evolution of SFPs across 11 passerine species and found a significantly higher rate of positive selection in SFPs compared with the rest of the genome, as well as significant enrichments for functional pathways related to immunity in the set of positively selected SF genes. Our results suggest that selection on immunity pathways is an important determinant of passerine SF composition and evolution. Assessing the role of immunity genes in speciation in other recently diverged taxa should be prioritized given the potential role for immunity-related proteins in reproductive incompatibilities in Passer sparrows.

Dietary plant extracts modulate gene expression profiles in alveolar macrophages of pigs experimentally infected with porcine reproductive and respiratory syndrome virus

BACKGROUND

Our previous study showed that 3 plant extracts enhanced the immune responses and growth efficiency of weaned pigs infected with porcine reproductive and respiratory syndrome virus (PRRSV), which is one of the most economically important disease in swine industry. However, each plant extract differently effected on growth efficiency and immune responses. Therefore, the objective of this study was conducted to characterize the effects and investigate the potential underlying mechanisms of 3 plant extracts on gene expression of alveolar macrophages in weaned pigs experimentally infected with PRRSV.

RESULTS

PRRSV infection altered (P < 0.05) the expression of 1,352 genes in pigs fed the control (CON; 755 up, 597 down). Compared with the infected CON, feeding capsicum (CAP), garlic botanical (GAR), or turmeric oleoresin (TUR) altered the expression of 46 genes (24 up, 22 down), 134 genes (59 up, 75 down), or 98 genes (55 up, 43 down) in alveolar macrophages of PRRSV-infected pigs, respectively. PRRSV infection up-regulated (P < 0.05) the expression of genes related to cell apoptosis, immune system process, and response to stimulus, but down-regulated (P < 0.05) the expression of genes involved in signaling transduction and innate immune response. Compared with the infected CON, feeding TUR or GAR reduced (P < 0.05) the expression of genes associated with antigen processing and presentation, feeding CAP up-regulated (P < 0.05) the expression of genes involved in antigen processing and presentation. Supplementation of CAP, GAR, or TUR also enhanced (P < 0.05) the expression of several genes related to amino acid metabolism, steroid hormone synthesis, or RNA degradation, respectively.

CONCLUSIONS

The results suggest that 3 plant extracts differently regulated the expression of genes in alveolar macrophages of PRRSV-infected pigs, especially altering genes involved in immunity.

Mating to Intact, but Not Vasectomized, Males Elicits Changes in the Endometrial Transcriptome: Insights From the Bovine Model

An appropriate female reproductive environment is essential for pregnancy success. In several species, including mice, pigs and horses, seminal plasma (SP) components have been shown to modulate this environment, leading to increased embryo viability and implantation. Due to the characteristics of mating in the aforementioned species, SP comes into direct contact with the uterus. However, it is questionable whether any SP reaches the uterus in species that ejaculate inside the vagina, such as humans and cattle. Hence, we hypothesized that sperm, perhaps acting as a vehicle for SP factors, play a more important role in the modulation of the maternal uterine environment in these species. In addition, changes elicited by SP and/or sperm may originate in the vagina and propagate to more distal regions of the female reproductive tract. To test these hypotheses, a bovine model in which heifers were mated to intact or vasectomized bulls or were left unmated was used. RNA-sequencing of endometrial samples collected 24 h after mating with a vasectomized bull did not reveal any differentially expressed genes (DEGs) in comparison with control samples. However, the endometrium of heifers mated with intact bulls exhibited 24 DEGs when compared to heifers mated with vasectomized bulls, and 22 DEGs when compared to unmated control heifers. The expression of a set of cytokines (IL6, IL1A, IL8, and TNFA) and candidate genes identified in the endometrial RNA-sequencing (PLA2G10, CX3CL1, C4BPA, PRSS2, BLA-DQB, and CEBPD) were assessed by RT-qPCR in the vagina and oviductal ampulla. No differences in expression of these genes were observed between treatments in any region. However, mating to both intact and vasectomized bulls induced an increase in IL1A and TNFA expression in the vagina compared to the oviduct. These data indicate that sperm, but not secretions from the accessory glands alone, induce modest changes in endometrial gene expression after natural mating in cattle. However, it is not clear whether this effect is triggered by inherent sperm proteins or SP proteins bound to sperm surface at the time of ejaculation.

Complement: The Emerging Architect of the Developing Brain

Complement activation products have long been associated with roles in the innate immune system, linking the humoral and cellular responses. However, among their recently described non-inflammatory roles, complement proteins also have multiple emerging novel functions in brain development. Within this context, separate proteins and pathways of complement have carved out physiological niches in the formation, development, and refinement of neurons. They demonstrate actions that are both reminiscent of peripheral immune actions and removed from them. We review here three key roles for complement proteins in the developing brain: progenitor proliferation, neuronal migration, and synaptic pruning.

Complement in stem cells and development

From its discovery in the late nineteenth century, as a 'complement' to the cellular immune response, the complement system has been widely affirmed as a powerful controller of innate and adaptive immune responses. In recent decades however, new roles for complement have been discovered, with multiple complement proteins now known to function in a broad array of non-immune systems. This includes during development, where complement exerts control over stem cell populations from fertilization and implantation throughout embryogenesis and beyond post-natal development. It is involved in processes as diverse as cell localisation, tissue morphogenesis, and the growth and refinement of the brain. Such physiological actions of complement have also been described in adult stem cell populations, with roles in proliferation, differentiation, survival, and regeneration. With such a broad range of complement functions now described, it is likely that current research only describes a fraction of the full reach of complement proteins. Here, we review how complement control of physiological cell processes has been harnessed in stem cell populations throughout both development and in adult physiology.

Seminal plasma and cryopreservation alter ram sperm surface carbohydrates and interactions with neutrophils

Spermatozoa deposited vaginally must navigate the physical, chemical and immune barriers of the cervix to reach the site of fertilisation. Characteristics that favour successful cervical transit remain largely unknown beyond the obvious factors of motility and viability. Epididymal and cryopreserved ram spermatozoa demonstrate poor cervical transit, for unknown reasons. We hypothesised that seminal plasma exposure and cryopreservation alter the surface sugars of these sperm populations and, consequently, their interaction with immune cells, both potential factors for successful cervical transit. The carbohydrate profiles of epididymal, ejaculated and frozen–thawed ram spermatozoa were assessed by flow cytometry and western blotting using lectins for galactose, sialic acid, N-acetylglucosamine and mannose. Seminal plasma exposure and cryopreservation caused significant changes to the relative amounts of surface sugars detected by flow cytometry and lectin blotting. Immune cell interaction was characterised using a neutrophil-binding assay. Seminal plasma acted as a robust protective mechanism, limiting binding of spermatozoa, whereas the media used for cryopreservation caused a significant disruption to opsonin-mediated binding. We were unable to demonstrate a link between changes to surface sugars and neutrophil susceptibility. Seminal plasma and cryopreservation clearly alter the sperm glycocalyx, as well as the interaction of spermatozoa with immune cells.

Clusterin in the mouse epididymis: possible roles in sperm maturation and capacitation

Clusterin (CLU) is known as an extracellular chaperone for proteins under stress, thus preventing them from aggregation and precipitation. We showed herein that CLU, expressed by principal cells of the mouse caput epididymis, was present in high amounts in the lumen. In the cauda epididymis, CLU bound tightly to the sperm head surface and its amount on total sperm was similar to that in the bathing luminal fluid. In both immotile and motile caudal epididymal sperm, CLU was localized over the entire sperm head except at the convex ridge, although in the motile sperm population, the CLU immunofluorescence pattern was distinctively mottled with a lower intensity. However, when motile sperm became capacitated, CLU was relocalized to the head hook region, with immunofluorescence intensity being higher than that on the non-capacitated counterparts. Under a slightly acidic pH of the epididymal lumen, CLU may chaperone some luminal proteins and deliver them onto the sperm surface. Immunoprecipitation of epididymal fluid proteins indicated that CLU interacted with SED1, an important egg-binding protein present in a high amount in the epididymal lumen. In a number of non-capacitated sperm, fractions of SED1 and CLU co-localized, but after capacitation, SED1 and CLU dissociated from one another. While CLU moved to the sperm head hook, SED1 translocated to the head convex ridge, the egg-binding site. Overall, CLU localization patterns can serve as biomarkers of immotile sperm, and non-capacitated and capacitated sperm in mice. The chaperone role of CLU may also be important for sperm maturation and capacitation.

Analysis of bull (Bos taurus) seminal vesicle fluid proteome in relation to seminal plasma proteome

The existing knowledge on the bull seminal vesicle proteome, a major seminal plasma constituent, and its relationship with seminal plasma is limited. This knowledge is prerequisite for a better understanding of seminal plasma variability, which is linked to semen quality. The objective of this study was to characterize the proteomes of seminal vesicle fluid and seminal plasma and to compare them to better understand the origin of seminal plasma proteins. We collected ejaculates and seminal vesicle fluid postmortem from 6 mature Holstein Friesian bulls. We performed the analysis and identification of proteins using 2-dimensional electrophoresis coupled with matrix-assisted laser desorption/ionization mass spectrometry. We identified 105 proteins in bull seminal vesicle fluid and 88 proteins in seminal plasma. For both seminal vesicles and seminal plasma proteins described in our study, top biological functions were cellular movement, cell death and survival, and cellular growth and proliferation. Additionally, seminal vesicle fluid proteins were involved in protein degradation and synthesis. Seminal plasma proteins were also involved in cellular assembly and organization and cell-to-cell signaling and interactions. Proteins of both fluids were involved in the following canonical pathways: glycolysis, gluconeogenesis, liver X receptor/farnesoid X receptor, and farnesoid X receptor/retinoid X receptor activation. Additionally, seminal vesicle fluid proteins appeared to be involved in oxidative stress response mediated by nuclear factor E2-related factor 2. Our results described the bull seminal vesicle fluid proteome for the first time and allowed for significant expansion of the current knowledge on the bull seminal plasma proteome. Moreover, analysis indicated that both bull seminal vesicle fluid and seminal plasma proteomes contained interconnected protein groups related to protective functions, glycolysis, and the morphology and physiology of the spermatozoa. These proteins and their interactions could be targeted in future research.

CD59 Regulation by SOX2 Is Required for Epithelial Cancer Stem Cells to Evade Complement Surveillance

Cancer stem cells (CSCs) are highly associated with therapy resistance and metastasis. Interplay between CSCs and various immune components is required for tumor survival. However, the response of CSCs to complement surveillance remains unknown. Herein, using stem-like sphere-forming cells prepared from a mammary tumor and a lung adenocarcinoma cell line, we found that CD59 was upregulated to protect CSCs from complement-dependent cytotoxicity. CD59 silencing significantly enhanced complement destruction and completely suppressed tumorigenesis in CSC-xenografted nude mice. Furthermore, we identified that SOX2 upregulates CD59 in epithelial CSCs. In addition, we revealed that SOX2 regulates the transcription of mCd59b, leading to selective mCD59b abundance in murine testis spermatogonial stem cells. Therefore, we demonstrated that CD59 regulation by SOX2 is required for stem cell evasion of complement surveillance. This finding highlights the importance of complement surveillance in eliminating CSCs and may suggest CD59 as a potential target for cancer therapy.

Toward Understanding the Genetic Basis of Yak Ovary Reproduction: A Characterization and Comparative Analyses of Estrus Ovary Transcriptiome in Yak and Cattle

Background

Yaks (Bos grunniens) are endemic species that can adapt well to thin air, cold temperatures, and high altitude. These species can survive in harsh plateau environments and are major source of animal production for local residents, being an important breed in the Qinghai–Tibet Plateau. However, compared with ordinary cattle that live in the plains, yaks generally have lower fertility. Investigating the basic physiological molecular features of yak ovary and identifying the biological events underlying the differences between the ovaries of yak and plain cattle is necessary to understand the specificity of yak reproduction. Therefore, RNA-seq technology was applied to analyze transcriptome data comparatively between the yak and plain cattle estrous ovaries.

Results

After deep sequencing, 3,653,032 clean reads with a total of 4,828,772,880 base pairs were obtained from yak ovary library. Alignment analysis showed that 16992 yak genes mapped to the yak genome, among which, 12,731 and 14,631 genes were assigned to Gene Ontology (GO) categories and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Furthermore, comparison of yak and cattle ovary transcriptome data revealed that 1307 genes were significantly and differentially expressed between the two libraries, wherein 661 genes were upregulated and 646 genes were downregulated in yak ovary. Functional analysis showed that the differentially expressed genes were involved in various Gene Ontology (GO) categories and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. GO annotations indicated that the genes related to “cell adhesion,” “hormonal” biological processes, and “calcium ion binding,” “cation transmembrane transport” molecular events were significantly active. KEGG pathway analysis showed that the “complement and coagulation cascade” pathway was the most enriched in yak ovary transcriptome data, followed by the “cytochrome P450” related and “ECM–receptor interaction” pathways. Moreover, several novel pathways, such as “circadian rhythm,” were significantly enriched despite having no evident associations with the reproductive function.

Conclusion

Our findings provide a molecular resource for further investigation of the general molecular mechanism of yak ovary and offer new insights to understand comprehensively the specificity of yak reproduction.

Sperm Proteome Maturation in the Mouse Epididymis

In mammals, transit through the epididymis, which involves the acquisition, loss and modification of proteins, is required to confer motility and fertilization competency to sperm. The overall dynamics of maturation is poorly understood, and a systems level understanding of the complex maturation process will provide valuable new information about changes occurring during epididymal transport. We report the proteomes of sperm collected from the caput, corpus and cauda segments of the mouse epididymis, identifying 1536, 1720 and 1234 proteins respectively. This study identified 765 proteins that are present in sperm obtained from all three segments. We identified 1766 proteins that are potentially added (732) or removed (1034) from sperm during epididymal transit. Phenotypic analyses of the caput, corpus and cauda sperm proteomes identified 60 proteins that have known sperm phenotypes when mutated, or absent from sperm. Our analysis indicates that as much as one-third of proteins with known sperm phenotypes are added to sperm during epididymal transit. GO analyses revealed that cauda sperm are enriched for specific functions including sperm-egg recognition and motility, consistent with the observation that sperm acquire motility and fertilization competency during transit through the epididymis. In addition, GO analyses revealed that the immunity protein profile of sperm changes during sperm maturation. Finally, we identified components of the 26S proteasome, the immunoproteasome, and a proteasome activator in mature sperm.

Epididymal C4b-binding protein is processed and degraded during transit through the duct and is not essential for fertility

C4b-binding protein (C4BP) is known as one of the circulating complement regulators that prevents excessive activation of the host-defense complement system. We have reported previously that C4BP is expressed abundantly in the rodent epididymis, one of the male reproductive organs connecting the testis and vas deferens, where immature spermatozoa acquire their motility and fertilizing ability during their transit through the duct. Epididymal C4BP (EpC4BP) is synthesized androgen-dependently by the epithelial cells, secreted into the lumen, and bound to the outer membrane of the passing spermatozoa. In this study, we found that EpC4BP is secreted as a large oligomer, similar to the serum C4BP, but is digested during the epididymal transit and is almost lost from both the luminal fluid and the sperm surface in the vas deferens. Such a processing pattern is not known in serum C4BP, suggesting that EpC4BP and serum C4BP might have different functional mechanisms, and that there is a novel function of EpC4BP in reproduction. In addition, the disappearance of EpC4BP from the sperm surface prior to ejaculation suggests that EpC4BP works only in the epididymis and would not work in the female reproductive tract to protect spermatozoa from complement attack. Next, we generated C4BP-deficient (C4BP-/-) mice to examine the possible role of EpC4BP in reproduction. However, the C4BP-/- mice were fertile and no significant differences were observed between the C4BP-/- and wild-type mouse spermatozoa in terms of morphology, motility, and rate of the spontaneous acrosome reaction. These results suggest that EpC4BP is involved in male reproduction, but not essential for sperm maturation.

Drosophila sperm proteome evolution: Insights from comparative genomic approaches

Despite their conserved functional role in sexually reproducing organisms, spermatozoa are a diverse and rapidly evolving cell type. This phenomenon is largely attributed to sexual selection in polygamous species where sperm from multiple males compete to fertilize a limited number of oocytes. Drosophila have proven to be a particularly informative model system for the study of spermatogenesis and in this review we discuss how the characterization of the Drosophila melanogaster sperm proteome has advanced our understanding of the evolutionary genomics of sperm form and function. We summarize the molecular evolutionary characteristics of sperm genes and highlight recent evidence demonstrating the importance of novel gene creation in the evolution of sperm function and competitive ability. Comparative proteomic evidence is also provided, supporting an overall functional conservation between the Drosophila and mouse sperm proteomes. This analysis reveals a diverse repertoire of proteins functioning in proteolytic pathways, as well as the presence of proteins of the complement and innate immunity systems. We propose that these pathways may have functional relevance to post-mating female immunological responses as well as coevolved interactions with pathways expressed in the female reproductive tract, including those involved in sperm-oocyte recognition and fertilization.

Morbillivirus receptors and tropism: multiple pathways for infection

Morbilliviruses, which include measles virus (MeV), canine distemper virus, and rinderpest virus, are among the most important pathogens in their respective hosts and cause severe syndromes. Morbilliviruses are enveloped viruses with two envelope proteins, one of which is hemagglutinin (H) protein, which plays a role in binding to cellular receptors. During morbillivirus infection, the virus initially targets lymphoid cells and replicates efficiently in the lymph nodes. The principal cellular receptor for morbillivirus is signaling lymphocyte activation molecule (SLAM, also called CD150), which is exclusively expressed on immune cells. This feature reflects the strong lymphoid cell tropism and viral spread in the infected body. Morbillivirus infection, however, affects various tissues in the body, including the lung, kidney, gastrointestinal tract, vascular endothelium, and brain. Thus, other receptors for morbilliviruses in addition to SLAM might exist. Recently, nectin-4 has been identified as a novel epithelial cell receptor for MeV. The expression of nectin-4 is localized to polarized epithelial cells, and this localization supports the notion of cell tropism since MeV also grows well in the epithelial cells of the respiratory tract. Although two major receptors for lymphoid and epithelial cells in natural infection have been identified, morbillivirus can still infect many other types of cells with low infectivity, suggesting the existence of inefficient but ubiquitously expressed receptors. We have identified other molecules that are implicated in morbillivirus infection of SLAM-negative cells by alternative mechanisms. These findings indicate that morbillivirus utilizes multiple pathways for establishment of infection. These studies will advance our understanding of morbillivirus tropism and pathogenesis.

Immunophysiology and pathology of inflammation in the testis and epididymis

The ability of spermatogenic cells to evade the host immune system and the ability of systemic inflammation to inhibit male reproductive function represent two of the most intriguing conundrums of male reproduction. Clearly, an understanding of the underlying immunology of the male reproductive tract is crucial to resolving these superficially incompatible observations. One important consideration must be the very different immunological environments of the testis, where sperm develop, and the epididymis, where sperm mature and are stored. Compared with the elaborate blood-testis barrier, the tight junctions of the epididymis are much less effective. Unlike the seminiferous epithelium, immune cells are commonly observed within the epithelium, and can even be found within the lumen, of the epididymis. Crucially, there is little evidence for extended allograft survival (immune privilege) in the epididymis, as it exists in the testis, and the epididymis is much more susceptible to loss of immune tolerance. Moreover, the incidence of epididymitis is considerably greater than that of orchitis in humans, and susceptibility to sperm antibody formation after damage to the epididymis or vas deferens increases with increasing distance of the damage from the testis. Although we still know relatively little about testicular immunity, we know less about the interactions between the epididymis and the immune system. Given that the epididymis appears to be more susceptible to inflammation and immune reactions than the testis, and thereby represents the weaker link in protecting developing sperm from the immune system, it is probably time this imbalance in knowledge was addressed.

CD46 processing: a means of expression

CD46 is a ubiquitously expressed type I transmembrane protein, first identified as a regulator of complement activation, and later as an entry receptor for a variety of pathogens. The last decade has also revealed the role of CD46 in regulating the adaptive immune response, acting as an additional costimulatory molecule for human T cells and inducing their differentiation into Tr1 cells, a subset of regulatory T cells. Interestingly, CD46 regulatory pathways are defective in T cells from patients with multiple sclerosis, asthma and rheumatoid arthritis, illustrating its importance in regulating T cell homeostasis. Indeed, CD46 expression at the cell surface is tightly regulated in many different cell types, highlighting its importance in several biological processes. Notably, CD46 is the target of enzymatic processing, being cleaved by metalloproteinases and by the presenilin/gamma secretase complex. This processing is required for its functions, at least in T cells. This review will summarize the latest updates on the regulation of CD46 expression and on its effects on T cell activation.

CD46 in innate and adaptive immunity: an update

CD46 was discovered in 1986 during a search for novel C3b-binding proteins. CD46 is expressed ubiquitously and functions as a co-factor in the factor I-mediated proteolytic cleavage of C3b and C4b. Its vital role in preventing complement deposition on host tissue is underpinned by the fact that deficiency of CD46 is a predisposing factor for numerous disease conditions arising from complement-mediated 'self-attack'. However, in the last 10 years, it has become apparent that CD46 is also heavily involved in a new and somewhat surprising functional aspect of the complement system: the down-modulation of adaptive T helper type 1 (Th1) immune responses by regulating the production of interferon (IFN)-γ versus interleukin (IL)-10 within these cells. Specifically, this latter function of CD46 is a tantalizing discovery - it may not only have delivered the explanation as to why so many pathogens use and abuse CD46 as cell entry receptor but clearly has important clinical implications for the better understanding of Th1-mediated disease states and novel therapeutic approaches for their amelioration. Here, we summarize and discuss the current knowledge about CD46 and its expanding roles in the immune system.

Potential role of multiple members of the kallikrein-related peptidase family of serine proteases in activating latent TGF beta 1 in semen

Transforming growth factor beta1 (TGF beta 1) has been implicated as a key contributor of immunosuppression in seminal plasma. The biochemical mechanisms that lead to production of active seminal TGF beta 1 are not fully understood. It is plausible that TGF beta 1 activation is partly induced simultaneously with the release of motile spermatozoa following liquefaction of the semen coagulum. Several members of the kallikrein-related peptidase (KLK) family are involved in the regulation of semen liquefaction. This study examines the involvement of these KLKs in TGF beta 1 activation in vitro and ex vivo, in seminal plasma. Latent TGF beta 1 was rapidly activated by KLK14. The latency-associated propeptide (LAP) was shown to be cleaved by KLK14 into small peptide fragments, providing a possible mechanism for TGF beta 1 activation. KLK14 also cleaved the latent TGFbeta binding protein 1 (LTBP1). KLK1, 2, and 5 might also contribute to TGF beta 1 activation by nicking the LAP motif and inducing conformational changes that aid in subsequent processing of LAP or through LTBP1 cleavage. Our study provides strong evidence for the involvement of multiple members of the seminal KLK cascade in activation of latent TGF beta 1 in seminal plasma. These findings might have clinical implications in infertility treatment of cases with concurrent delayed liquefaction and TGF beta 1-related semen antigenicity.

Sperm proteomics reveals intensified selection on mouse sperm membrane and acrosome genes

Spermatozoa are a focal point for the impact of sexual selection due to sperm competition and sperm-female interactions in a wide range of sexually reproducing organisms. In-depth molecular investigation of the ramifications of these selective regimes has been limited due to a lack of information concerning the molecular composition of sperm. In this study, we utilize three previously published proteomic data sets in conjunction with our whole mouse sperm proteomic analysis to delineate cellular regions of sperm most impacted by positive selection. Interspecific analysis reveals robust evolutionary acceleration of sperm cell membrane genes (which include genes encoding acrosomal and sperm cell surface proteins) relative to other sperm genes, and evidence for positive selection in approximately 22% of sperm cell membrane components was obtained using maximum likelihood models. The selective forces driving the accelerated evolution of these membrane proteins may occur at a number of locations during sperm development, maturation, and transit through the female reproductive tract where the sperm cell membrane and eventually the acrosome are exposed to the extracellular milieu and available for direct cell-cell interactions.

Immunology of the Testis and Male Reproductive Tract

A large body of evidence points to the existence of a close, dynamic relationship between the immune system and the male reproductive tract, which has important implications for our understanding of both systems. The testis and the male reproductive tract provide an environment that protects the otherwise highly immunogenic spermatogenic cells and sperm from immunological attack. At the same time, secretions of the testis, including androgens, influence the development and mature functions of the immune system. Activation of the immune system has negative effects on both androgen and sperm production, so that systemic or local infection and inflammation compromise male fertility. The mechanisms underlying these interactions have begun to receive the attention from reproductive biologists and immunologists that they deserve, but many crucial details remain to be uncovered. A complete picture of male reproductive tract function and its response to toxic agents is contingent upon continued exploration of these interactions and the mechanisms involved.

Factor H in porcine seminal plasma protects sperm against complement attack in genital tracts

We found that factor H (FH) exists in porcine seminal plasma. Purified FH strongly inhibited serum alternative pathway complement activation against lipopolysaccharide. The molecular weight, pI, and heparin-binding activity of the purified protein were different from those of purified FH from porcine serum. The complement regulatory activity of seminal plasma FH was approximately 2-fold stronger than that of serum FH. Treatment of purified serum FH with sialidase and N-glycosidase F gave almost the same results as those of seminal plasma FH. The deletion of sialic acid from the carbohydrate chains of both FHs contributed to heparin-binding and complement regulatory activities. Results of reverse transcriptase-PCR, Western blot analysis, and immunohistochemistry showed that seminal plasma FH is mainly secreted from epithelial cells of the seminal vesicle in male genital tracts. FH was also detected in the outer acrosomal region of ejaculated sperm by immunofluorescence staining, and found that the purified FH from the sperm membrane has the same complement regulatory activity as that of seminal plasma FH. The ejaculated sperm possessing FH in the outer acrosomal region considerably evaded complement attack. We also found that there is strong complement activity in fluids from female genital tract ducts. These findings indicate that FH bound to the outer acrosomal region and soluble FH play important roles in protecting sperm against complement attack in male and female genital tracts.

Measles virus and CD46

Measles virus (MV) was isolated in 1954 (Enders and Peeble 1954). It is among the most contagious of viruses and a leading cause of mortality in children in developing countries (Murray and Lopez 1997; Griffin 2001; Bryce et al. 2005). Despite intense research over decades on the biology and pathogenesis of the virus and the successful development in 1963 of an effective MV vaccine (Cutts and Markowitz 1994), cell entry receptor(s) for MV remained unidentified until 1993. Two independent studies showed that transfection of nonsusceptible rodent cells with human CD46 renders these cells permissive to infection with the Edmonston and Halle vaccine strains of measles virus (Dorig et al. 1993; Naniche et al. 1993). A key finding in these investigations was that MV binding and infection was inhibited by monoclonal and polyclonal antibodies to CD46. These reports established CD46 as a MV cell entry receptor. This chapter summarizes the role of CD46 in measles virus infection.

The pentraxin serum amyloid P component is found in the male genital tract and attached to spermatozoa

Serum amyloid P component (SAP) belongs to the pentraxin family of proteins, members of which are characterized by radial pentameric structure and calcium-dependent ligand binding. SAP is present in all types of amyloidosis and has been shown to bind to several ligands, but the physiological function of this protein has not been fully elucidated. The present study identified and characterized SAP in human semen and immunolocalized it to the male reproductive tract. SAP was also detected in seminal plasma by immunoblotting and purification by affinity chromatography followed by mass spectrometry. According to electroimmunoassay, the concentration of SAP in semen is approximately 2 mg/L, and flow cytometry revealed SAP attached to the surface of spermatozoa. Moreover, immunohistochemistry showed positive staining of spermatozoa, subsets of epithelial cells, and the stroma of accessory male genital glands and testis. Presence of mRNA supports local production of SAP, as shown with reverse transcription polymerase chain reaction. We identified SAP in a new setting - the human male reproductive system. SAP was detected on ejaculated spermatozoa, in seminal plasma and in tissue sections from the male reproductive tract. Further functional studies are needed to explain the role of SAP in human reproduction.

Immunization with autologous CD46 generates a strong autoantibody response in rats that targets spermatozoa

CD46, a membrane complement regulator, has been implicated as pathogen receptor, T cell activator and contributor to spermatozoa-egg interactions. In man, a role in the fertilization process was suggested by its localization on the acrosome. In rodents, CD46 is expressed only on the spermatozoal acrosome, suggesting an essential role at this site. This restricted expression led us to ask whether immunization with CD46 would generate anti-CD46 antibody responses that might target spermatozoa and influence fertility. We immunized male and female rats with rat CD46. Strong immune responses were generated in all rats and immune sera stained CD46 in testis extracts and in situ in testis and sperm. Incubation of spermatozoa with immune sera caused deposition of immunoglobulin and C3b in an acrosome pattern and reduced motility. We mated immune male rats with naïve females and female immune rats with naïve males. The incidence of pregnancy and number of fetuses were not different in matings involving immune male or female rats compared to controls. Testis sections from immune rats revealed no immunoglobulin deposition on CD46-positive sperm precursors, suggesting that acrosomal CD46 was inaccessible in this location. A minority of spermatozoa harvested from epididymis of immune rats had immunoglobulin and C3b bound to the acrosome, suggesting that anti-CD46, present in genital tract fluids, bound after acrosome reaction. These data demonstrate that the restricted expression of CD46 allows strong anti-CD46 responses in rats that target spermatozoa in vitro and in vivo. The anti-CD46 response did not influence fertility, perhaps reflecting the considerable redundancy for fertilization in rodents.

The influence of pre- and post-ovulatory insemination and early pregnancy on the infiltration by cells of the immune system in the sow oviduct

The aim of this study was to investigate the influence of pre- and post-ovulatory insemination and early pregnancy on the distribution of immune cells in the oviduct. Eighteen sows were pre-ovulatory and sixteen sows were post-ovulatory inseminated and slaughtered at different times, 5-6 h after insemination, 20-25 h and approximately 70 h after ovulation, day 11 and day 19. Immediately after slaughter, oviductal samples of three different segments (isthmus, ampulla and infundibulum) were fixed, embedded in plastic resin and stained with toluidine blue or cryofixed and stored in a freezer at -70 degrees C until analysed by immunohistochemistry (pre-ovulatory inseminated sows) with an avidin-biotin peroxidase method. Quantitative and qualitative examinations of oviductal epithelium and subepithelial connective tissue were performed by light microscopy. After pre- or post-ovulatory insemination, neutrophils were not observed in the oviductal epithelium from any of the segments or groups. The numbers of intraepithelial lymphocytes of all sows as well as CD2- and CD3-positive cells of the pre-ovulatory inseminated sows were higher in the infundibulum than in the other segments (p < or = 0.001). In the subepithelial connective tissue of the pre-ovulatory inseminated sows, significantly higher numbers of lymphocytes (p < or = 0.001) and plasma cells (p < or = 0.001) were found in infundibulum than in isthmus. Neutrophils were found mainly in infundibulum, the number approximately 40 h after pre-ovulatory insemination was significantly higher (p < or = 0.05) than in the other groups and segments. Significantly higher numbers of CD2 than CD3-positive cells were found for all groups and segments. In the subepithelial connective tissue of post-ovulatory inseminated sows, the numbers of lymphocytes was higher (p < or = 0.001) at day 19 than up to 50 h after insemination and lower (p < or = 0.001) in isthmus than in ampulla and infundibulum. Neutrophils were found in infundibulum in almost all groups and the number was significantly higher (p < or = 0.05) in the infundibulum up to 50 h after insemination than in other segments. In the oviductal epithelium, no influence of insemination was found on the presence of phagocytes, i.e. neutrophils and macrophages, but on lymphocytes. In the infundibular connective tissue, pre-ovulatory insemination had an effect on neutrophil distribution, indicating an active immune response to insemination in the upper segment. Post-ovulatory insemination changed the oviductal immune cell pattern.

CD55 in rat male reproductive tissue: Differential expression in testis and expression of a unique truncated isoform on spermatozoa

CD55 is a key regulator of complement activation, expressed on most tissues and cells in man and other mammals. In the rat, alternative splicing in the gene encoding CD55 yields GPI-anchored (GPI-CD55) and transmembrane (TM-CD55) forms. Published Northern blot analysis indicated that while GPI-CD55 was broadly expressed, TM-CD55 was primarily expressed in the testis, although the precise site of expression was not identified. To clarify the distribution of CD55 isoforms in rat reproductive tissues, we first performed immunohistochemistry and Western blot analysis with an anti-rat CD55 mAb that recognized all reported CD55 isoforms, and a polyclonal immunoglobulin specific for TM-CD55. CD55 was absent in testis prior to puberty. Post-puberty, CD55 was expressed at high levels on all spermiogenic cells from step 6 spermatid onward, and on mature spermatozoa focussed on the acrosome, but was absent from support cells and early progenitors. Enzymatic digestion revealed that GPI-CD55 was predominant in testis and spermatozoa. Staining for TM-CD55 with specific immunoglobulin confirmed its absence from mature sperm and expression on spermatids only between steps 11 and 14 of development. GPI-CD55 on spermatozoa was of lower molecular weight than that in testis and other tissues; sequencing from spermatozoal mRNA identified a unique isoform of GPI-CD55 missing short consensus repeat 4. The predominant acrosome expression and presence of a unique, truncated isoform of CD55 on spermatozoa provides further support for the hypothesis that the acrosome is a highly specialized region in which closely regulated complement activation may contribute to reproductive function.

T-cell regulation: with complements from innate immunity

The complement system was traditionally known as an effector arm of humoral immunity. Today we also recognize it as a main element of the innate immune system. In blood and other body fluids complement is a first line of defence against pathogens, because it becomes fully active within seconds. Active complement fragments attach to the invading pathogen to promote opsonization and lysis, triggering a local inflammatory response. This Review focuses on the evolving role of the complement system in the regulation of T-cell responses, from directing the initiation phase, through driving lineage commitment, to regulating the contraction phase.

The complement regulatory proteins CD55 (decay accelerating factor) and CD59 are expressed on the inner acrosomal membrane of human spermatozoa as well as CD46 (membrane cofactor protein)

The complement regulatory proteins CD55 and CD59 are expressed on the plasma membrane of human spermatozoa, whereas CD46 is only on the inner acrosomal membrane (IAM) which becomes surfaced exposed after the acrosome reaction when sperm assume fertilisation-competence. CD55 & CD59, two glycosylphosphatidylinositol (GPI)-anchored proteins, have been detected previously in some studies also in the acrosomal region of chemically fixed spermatozoa but never demonstrated at this site on unfixed spermatozoa. Dual labelling immunofluorescence and confocal microscopy on fresh unfixed spermatozoa, with minimal subsequent time to fixation, has shown CD55 to be markedly expressed on the IAM, more than on the plasma membrane. However, unlike for CD46, CD55 displayed patchy staining over the acrosome, with some variation between individual spermatozoa. All IAM-associated CD55 was localised within GM1-containing lipid rafts. CD59 was expressed also on the IAM, but in a pronounced granular pattern with more variation observed from one spermatozoa to another. Both CD55 & CD59 were released from the IAM by PI-PLC, demonstrating them to be GPI-anchored. Analysis of acrosome-reacted spermatozoal CD55 by Western blotting revealed a novel single 55 kDa protein lacking significant oligosaccharides susceptible to glycosidases. Antibody-induced membrane rafting and release of CD55 & CD59 in vitro may have influenced previous results. Significant coexpression of CD55 & CD46 on the IAM suggests some functional cooperation at this site.

Expression and genomic organization of zonadhesin-like genes in three species of fish give insight into the evolutionary history of a mosaic protein

Background

The mosaic sperm protein zonadhesin (ZAN) has been characterized in mammals and is implicated in species-specific egg-sperm binding interactions. The genomic structure and testes-specific expression of zonadhesin is known for many mammalian species. All zonadhesin genes characterized to date consist of meprin A5 antigen receptor tyrosine phosphatase mu (MAM) domains, mucin tandem repeats, and von Willebrand (VWD) adhesion domains. Here we investigate the genomic structure and expression of zonadhesin-like genes in three species of fish.

Results

The cDNA and corresponding genomic locus of a zonadhesin-like gene (zlg) in Atlantic salmon (Salmo salar) were sequenced. Zlg is similar in adhesion domain content to mammalian zonadhesin; however, the domain order is altered. Analysis of puffer fish (Takifugu rubripes) and zebrafish (Danio rerio) sequence data identified zonadhesin (zan) genes that share the same domain order, content, and a conserved syntenic relationship with mammalian zonadhesin. A zonadhesin-like gene in D. rerio was also identified. Unlike mammalian zonadhesin, D. rerio zan and S. salar zlg were expressed in the gut and not in the testes.

Conclusion

We characterized likely orthologs of zonadhesin in both T. rubripes and D. rerio and uncovered zonadhesin-like genes in S. salar and D. rerio. Each of these genes contains MAM, mucin, and VWD domains. While these domains are associated with several proteins that show prominent gut expression, their combination is unique to zonadhesin and zonadhesin-like genes in vertebrates. The expression patterns of fish zonadhesin and zonadhesin-like genes suggest that the reproductive role of zonadhesin evolved later in the mammalian lineage.