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

CD81 is a receptor for equine arteritis virus (family: Arteriviridae)

Arteriviruses are a family of single-stranded, positive-sense RNA (+ssRNA) viruses that infect diverse animal hosts. Many arteriviruses are macrophage-tropic, consistent with their utilization of the macrophage-specific molecule CD163 as a receptor. However, the horse arterivirus (equine arteritis virus, EAV), which infects additional cell types beyond macrophages, does not utilize CD163 in its entry mechanism. Here, we use a genome-wide CRISPR knockout screen to identify alternative receptors that could explain this discrepancy in arterivirus receptor utilization and tropism, identifying the plasma membrane tetraspanin CD81 as a required host factor for EAV infection. Genetic knockout of CD81 or pre-incubation with soluble CD81 protected cells from infection with EAV, but had no impact on susceptibility to other arteriviruses. Bypassing the entry step of the viral life cycle by transfecting the EAV genome into CD81-knockout cells produced infectious EAV, implicating CD81 in the EAV entry process. Screening of CD81 orthologs from natural arterivirus hosts identified the brushtail possum CD81 as unsupportive of EAV entry, indicating that CD81 incompatibility can serve as a barrier to cross-species infection. Horse/possum CD81 chimeras were then used to map the structural domains of CD81 engaged by EAV, identifying alpha helix "D" on the large extracellular loop of CD81 as critical for EAV entry. This study identifies the first example of receptor switching in the Arteriviridae family and, given the broad tissue distribution of CD81 expression, suggests that the adoption of CD81 enabled an expansion of EAV tropism.IMPORTANCEArteriviruses are a family of diverse positive-sense RNA viruses that can infect a wide range of animal hosts, but many details regarding how arteriviruses gain entry into cells remain unclear. Most arteriviruses are thought to utilize the macrophage-specific molecule CD163 as a receptor; however, the horse arterivirus (equine arteritis virus, EAV) infects additional cell types beyond macrophages and does not utilize CD163. In this study, we identified the host factor CD81 as a significant player in EAV entry. Beyond the implications that this discovery holds for equine health, this study adds to the increasingly complex picture of arterivirus entry and demonstrates that these viruses are capable of adopting new host molecules as receptors, with consequences for the types of cells these viruses infect, the disease they cause, and their mode(s) of transmission.

The extracellular vesicle tetraspanin CD63 journey from the testis through the epididymis to mature bull sperm

The important role of extracellular vesicles, which are considered key mediators of intercellular communication under physiological and pathological conditions, in various cellular processes, including those crucial for mammalian reproduction, has been increasingly studied. Tetraspanins, including CD63, are widely used as markers of extracellular vesicles, but they may also play a role in their biogenesis, cargo selection, cell targeting, and uptake. This study aimed to map the journey of the extracellular vesicle protein tetraspanin CD63 from the testis through the epididymis into mature bull sperm via an approach that included immunohistochemistry (immunofluorescence and immunoperoxidase staining), Western blot analysis, and immunoprecipitation analysis. We described the presence of CD63 in bull testicular and epididymal tissues, extracellular vesicles produced in these organs and spermatozoa during epididymal transit and after ejaculation. In addition, we revealed the nonuniform distribution of potential CD63 partners, such as CD9, integrin αV and syntenin-1, in the sperm head and tail and in extracellular vesicles. These findings contribute to understanding the complex mechanisms underlying sperm maturation and point to the possible involvement of tetraspanins and their associated partners, either as part of extracellular vesicles or sperm membranes, in these processes.

Plasmodium vivax merozoite-specific thrombospondin-related anonymous protein (PvMTRAP) interacts with human CD36, suggesting a novel ligand-receptor interaction for reticulocyte invasion

BACKGROUND

The Plasmodium vivax merozoite restrictively invades immature erythrocytes, suggesting that its ligand(s) might interact with corresponding receptor(s) that are selectively abundant on reticulocytes to complete the invasion. Finding the ligand‒receptor interaction involved in P. vivax invasion is critical to vivax malaria management; nevertheless, it remains to be unraveled.

METHODS

A library of reticulocyte receptors and P. vivax ligands were expressed by a HEK293E mammalian cell expression system and were then used to screen the interaction using enzyme-linked immunosorbent assay (ELISA). A flow cytometry-based erythrocyte binding assay and bio-layer interferometry experiment were further utilized to cellularly and quantitatively identify the ligand‒receptor interaction, respectively.

RESULTS

Plasmodium vivax merozoite-specific thrombospondin-related anonymous protein (PvMTRAP) was found to interact with human CD36 using systematic screening. This interaction was specific at a molecular level from in vitro analysis and comparable to that of P. vivax Duffy binding protein (PvDBP) and Duffy antigen receptor for chemokines (DARC) (KD: 37.0 ± 1.4 nM and 7.7 ± 0.5 nM, respectively). Flow cytometry indicated that PvMTRAP preferentially binds to reticulocytes, on which CD36 is selectively present.

CONCLUSIONS

Human CD36 is selectively abundant on reticulocytes and is able to interact specifically with PvMTRAP, suggesting that it may function as a ligand and receptor during the invasion of reticulocytes by P. vivax.