Genome-wide identification of scavenger receptor family genes in Octopus sinensis and their immune response to PGN, poly I:C, and Vibrio parahaemolyticus.

Octopus sinensis is an important economic species in China that relies mainly on the innate immune system to resist pathogenic invasion. Scavenger receptors (SRs), as key members of pattern recognition receptors (PRRs), initiate immune responses by recognizing pathogen-associated molecular patterns (PAMPs). However, the composition and immune functions of SR family members in O. sinensis remain unclear. In this study, six OsSR genes were identified from the O. sinensis genome, all of which contain conserved SR family domains. These SRs were classified into five subclasses (A, B, E, H, and I), with one member in each subclass except subclass B, which contains two genes. Subcellular localization prediction revealed that MARCO, SRCRB4D, and MRC1 localize to the extracellular matrix, STAB2 and DMBT1 to both the extracellular matrix and plasma membrane, and SCARB1 to both the endoplasmic reticulum and plasma membrane-a distribution pattern that may support their differential immune recognition functions. Quantitative real-time PCR (qRT-PCR) analysis revealed that the six OsSR genes were expressed in eight normal tissues (including gill, hepatopancreas, and caecum) with varying expression levels. After stimulation with peptidoglycan (PGN), polyinosinic-polycytidylic acid (poly I:C), and Vibrio parahaemolyticus, the expression levels of OsSR genes in the hepatopancreas and gill showed significant upregulation at different time points (6 h, 12 h, 24 h, 48 h) (p < 0.05), while a few genes remained unchanged or were downregulated. Specifically, OsMARCO was significantly upregulated in both the gill and hepatopancreas after stimulation with PGN, poly I:C, and V. parahaemolyticus (p < 0.05); OsSCARB1 was significantly upregulated in both gill and hepatopancreas after V. parahaemolyticus stimulation (p < 0.05) but showed no significant change in gill tissues under PGN and poly I:C stimulation. These qRT-PCR results demonstrate that OsSRs are differentially regulated by pathogenic and PAMP challenges, thus not only defining their role in the transcriptional immune response but also laying a foundation for research on innate immune signaling pathways in cephalopods.