Tetraspanins in mammalian reproduction: spermatozoa, oocytes and embryos

Juno and CD9 protein network organization in oolemma of mouse oocyte

Juno and CD9 protein, expressed in oolemma, are known to be essential for sperm-oocyte binding and fusion. Although evidence exists that these two proteins cooperate, their interaction has not yet been demonstrated. Here in, we present Juno and CD9 mutual localization over the surface of mouse metaphase II oocytes captured using the 3D STED super-resolution technique. The precise localization of examined proteins was identified in different compartments of oolemma such as the microvillar membrane, planar membrane between individual microvilli, and the membrane of microvilli-free region. Observed variance in localization of Juno and CD9 was confirmed by analysis of transmission and scanning electron microscopy images, which showed a significant difference in the presence of proteins between selected membrane compartments. Colocalization analysis of super-resolution images based on Pearson's correlation coefficient supported evidence of Juno and CD9 mutual position in the oolemma, which was identified by proximity ligation assay. Importantly, the interaction between Juno and CD9 was detected by co-immunoprecipitation and mass spectrometry in HEK293T/17 transfected cell line. For better understanding of experimental data, mouse Juno and CD9 3D structure were prepared by comparative homology modelling and several protein-protein flexible sidechain dockings were performed using the ClusPro server. The dynamic state of the proteins was studied in real-time at atomic level by molecular dynamics (MD) simulation. Docking and MD simulation predicted Juno-CD9 interactions and stability also suggesting an interactive mechanism. Using the multiscale approach, we detected close proximity of Juno and CD9 within microvillar oolemma however, not in the planar membrane or microvilli-free region. Our findings show yet unidentified Juno and CD9 interaction within the mouse oolemma protein network prior to sperm attachment. These results suggest that a Juno and CD9 interactive network could assist in primary Juno binding to sperm Izumo1 as a prerequisite to subsequent gamete membrane fusion.

Extracellular vesicles would be involved in the release and delivery of seminal TGF-β isoforms in pigs

Introduction

Pig seminal plasma (SP) is rich in active forms of all three isoforms (1-3) of transforming growth factor β (TGF-β), a chemokine modulatory of the immune environment in the female genital tract once semen is delivered during mating or artificial insemination (AI). The present study aimed to examine how TGF-βs are secreted by the epithelium of the male reproductive tract and how they are transported in semen, emphasizing the interplay with seminal extracellular vesicles (sEVs).

Methods

Source of TGF-βs was examined by immunohistochemistry in testis, epididymis, and accessory sex glands, by immunocytochemistry in ejaculated spermatozoa, and by Luminex xMAP® technology in SP and sEVs retrieved from healthy, fertile male pigs used as breeders in AI programs.

Results

All three TGF-β isoforms were expressed in all reproductive tissues explored and would be released into ductal lumen either in soluble form or associated with sEVs. Ejaculated spermatozoa expressed all three TGF-β isoforms, both inside and outside, probably the outer one associated with membrane-bound sEVs. The results confirmed that pig SP contains all three TGF-β isoforms and demonstrated that a substantial portion of them is associated with sEVs.

Discussion

Seminal EVs would be involved in the cellular secretion of the active forms of seminal TGF-β isoforms and in their safe transport from the male to the female reproductive tract.

Significance of Complement Regulatory Protein Tetraspanins in the Male Reproductive System and Fertilization

Fertilization is a very sophisticated and unique process involving several key steps resulting in a zygote's formation. Recent research has indicated that some immune system-related cell surface molecules (CD molecules from the tetraspanin superfamily) may have a role in fertilization. Extracellular vesicles are undeniably involved in a variety of cellular functions, including reproduction. Tetraspanin proteins identified in extracellular vesicles are now used mostly as markers; mounting evidence indicates that they also participate in cell targeting, cargo selection, and extracellular vesicle formation. Their significance and potential in mammalian reproduction are currently being studied extensively. Despite the fact that the current data did not establish any theory, the crucial function of tetraspanins in the fertilization process was not ruled out, and the specific role of tetraspanins is still unknown. In this review, we bring insight into the existing knowledge regarding the expression of tetraspanins in spermatozoa and seminal fluid and their role in gamete binding and fusion.

Positive selection on ADAM10 builds species recognition in the synchronous spawning coral Acropora

The reef-building coral Acropora is a broadcast spawning hermaphrodite including more than 110 species in the Indo-Pacific. In addition, many sympatric species show synchronous spawning. The released gametes need to mate with conspecifics in the mixture of the gametes of many species for their species boundaries. However, the mechanism underlying the species recognition of conspecifics at fertilization remains unknown. We hypothesized that rapid molecular evolution (positive selection) in genes encoding gamete-composing proteins generates polymorphic regions that recognize conspecifics in the mixture of gametes from many species. We identified gamete proteins of Acropora digitifera using mass spectrometry and screened the genes that support branch site models that set the "foreground" branches showing strict fertilization specificity. ADAM10, ADAM17, Integrin α9, and Tetraspanin4 supported branch-site model and had positively selected site(s) that produced polymorphic regions. Therefore, we prepared antibodies against the proteins of A. digitifera that contained positively selected site(s) to analyze their functions in fertilization. The ADAM10 antibody reacted only with egg proteins of A. digitifera, and immunohistochemistry showed ADAM10 localized around the egg surface. Moreover, the ADAM10 antibody inhibited only A. digitifera fertilization but not the relative synchronous spawning species A. papillare. This study indicates that ADAM10 has evolved to gain fertilization specificity during speciation and contributes to species boundaries in this multi-species, synchronous-spawning, and species-rich genus.

Distribution of tetraspanins in bovine ovarian tissue and fresh/vitrified oocytes

Tetraspanin proteins are mostly known as organizers of molecular complexes on cell membranes, widely expressed on the surface of most nucleated cells. Although tetraspanins participate in many physiological processes of mammals, including reproduction, their relevance to the processes of folliculogenesis and oogenesis has not yet been fully elucidated. We bring new information regarding the distribution of tetraspanins CD9, CD81, CD151, CD82, and CD63 at different stages of follicular development in cattle. The found distribution of tetraspanin CD9, CD63, and integrin alpha V in similar areas of ovarian tissue outlined their possible cooperation. We also describe yet-unknown distribution patterns of CD151, CD82, and CD63 on immature and mature bovine oocytes. The unique localization of tetraspanins CD63 and CD82 in the zona pellucida of bovine oocytes suggested their involvement in transzonal projections. Furthermore, we present an unchanged distribution pattern of the studied tetraspanins in vitrified mature bovine oocytes. The immunofluorescent analysis was supplemented by in silico data addressing tetraspanins expression in the ovarian cells and oocytes across several species. The obtained results suggest that in the study of the oocyte development and potentially the fertilization process of cattle, the role of tetraspanins and integrins should also be taken into account.

CD9, a tetraspanin target for cancer therapy?

In the present minireview, we intend to provide a brief history of the field of CD9 involvement in oncogenesis and in the metastatic process of cancer, considering its potential value as a tumor-associated antigenic target. Over the years, CD9 has been identified as a favorable prognostic marker or predictor of metastatic potential depending on the cancer type. To understand its implications in cancer beside its use as an antigenic biomarker, it is essential to know its physiological functions, including its molecular partners in a given cell system. Moreover, the discovery that CD9 is one of the most specific and broadly expressed markers of extracellular membrane vesicles, nanometer-sized entities that are released into extracellular space and various physiological body fluids and play a role in intercellular communication under physiological and pathological conditions, notably the establishment of cancer metastases, has added a new dimension to our knowledge of CD9 function in cancer. Here, we will discuss these issues as well as the possible cancer therapeutic implications of CD9, their limitations, and pitfalls.

Exosomal Cargo May Hold the Key to Improving Reproductive Outcomes in Dairy Cows

The reproductive status of dairy cows remains a challenge for dairy farmers worldwide, with impaired fertility linked to a significant reduction in herd profitability, due in part to impaired immunity, increased metabolic pressure, and longer postpartum anestrous interval (PPAI). Exosomes are nanovesicles released from a variety of cell types and end up in circulation, and carry proteins, bioactive peptides, lipids, and nucleic acids specific to the place of origin. As such, their role in health and disease has been investigated in humans and animals. This review discusses research into exosomes in the context of reproduction in dairy herds and introduces recent advances in mass-spectrometry (MS) based proteomics that have a potential to advance quantitative profiling of exosomal protein cargo in a search for early biomarkers of cattle fertility.