In this study we demonstrated that Macrobrachium rosenbergii nodavirus (MrNV) was able to internalize and replicate in Sf9 insect cells, with levels of infection altered by substances affecting the caveolin-(CAV) mediated endocytosis pathway. The use of Sf9 cells for efficient MrNV replication and propagation was demonstrated by confocal microscopy and PCR amplification, through which early viral binding and internalization were initially detectable at 30min post-infection; whereas at 72h, the distinguishable sign of late-MrNV infection was observable as the gradual accumulation of a cytopathic effect (CPE) in the cells, ultimately resulting in cellular disruption. Moreover, during the early period of infection, the MrNV signals were highly co-localized with CAV1 signals of the CAV-mediated endocytosis pathway. The use of genistein as an inhibitor of the CAV-mediated endocytosis pathway significantly reduced MrNV and CAV1 co-localization, and also reduced the levels of MrNV infection in Sf9 cells as shown by PCR and ELISA. Moreover, the addition of the pathway agonist okadaic acid not only recovered but also augmented both the levels of MrNV co-localization with CAV1 and of Sf9 infection in the presence of genistein inhibition; therefore demonstrating that MrNV infection in Sf9 cells was associated with the CAV-mediated endocytosis pathway machinery.

Cathepsin D (CAT-D) is a well-known aspartic protease that serves a function as house-keeping lysosomal enzyme in all somatic cells. Its existence in reproductive tissues is highly variable, even in the somatic derived epithelial cells of reproductive tract. InMacrobrachium rosenbergii, existence of MrCAT-D and its translational product was detected in both somatic cells (Sertoli-like supporting cells) and developing spermatogenic cells as well as along accessory spermatic ducts. Specifically, MrCAT-D was localized onto the sperm surface rather than within the acrosomal matrix, as evident by similar staining pattern of anti-CAT-D on live and aldehyde fixed sperm. MrCAT-D in testicular extracts and sperm isolates showed active enzyme activities towards its specific fluorogenic substrate (MCA-Gly-Lys-Pro-Ile-Leu-Phe-Phe-Arg-Leu-Lys (Dnp)-D-Arg-NH₂). MrCAT-D also exerted its function towards hydrolyzing filamentous actin, the meshwork of which is shown to be localized at the junction between germ cells and supporting cells and spermatogonia inM. rosenbergiitesticular epithelium. Together, we have localized MrCAT-D transcript and its translational product in both supporting and germ cells of testis and claimed its enzymatic function towards actin degradation, which may be related to sperm release from the epithelial cell interaction.

Background and Aim: White spot syndrome virus (WSSV) is a devastating pathogen in shrimp aquaculture, with viral protein 28 (VP28) playing a critical role in host cell attachment and entry. The extracellular domain of VP28 (residues 35–95) is immunogenic and essential for infection; however, its receptor interaction mechanisms remain incompletely elucidated. This study aimed to evaluate the tissue-binding affinity of full-length VP28 and its derived peptides (P1: Residues 35–65; P2: Residues 66–95) as well as a multimeric chimeric virus-like particle (K5-VLP) displaying VP28 on the surface of Macrobrachium rosenbergii nodavirus capsids to enhance host tissue interaction. Materials and Methods: Recombinant VP28, synthetic peptides (P1, P2), and chimeric K5-VLP were produced and characterized. Binding and inhibition assays were performed using enzyme-linked immunosorbent assay and immunofluorescence microscopy on shrimp gill, hemocyte, muscle, stomach, and hepatopancreas tissues. Results: Full-length VP28 exhibited strong binding to gill, hemocyte, and muscle tissues. The P1 and P2 peptides showed moderate binding compared to rVP28. Notably, K5-VLP demonstrated a 1.7-fold higher binding affinity than rVP28 in gill tissues and significantly outperformed P1 and P2 peptides. Inhibition assays confirmed that K5-VLP more effectively interfered with VP28 binding than peptides. Structural analysis and transmission electron microscopy confirmed correct assembly and surface presentation of VP28 on the VLPs. Conclusion: Multimeric display of VP28 on K5-VLP enhances its binding affinity to shrimp tissues compared to monomeric or peptide forms. This suggests a promising platform for antiviral strategies, including competitive inhibition of WSSV entry and targeted therapeutic delivery in shrimp aquaculture. Keywords: aquaculture vaccines, Macrobrachium rosenbergii nodavirus, shrimp immunity, tissue binding, virus-like particles, viral protein 28, white spot syndrome virus.