Characterization, functional analysis, and expression of TNFR16 from Pinctada fucata martensii in response to exogenous stimuli and RNA interference

Marine pearls from Pinctada fucata martensii are valuable for decoration, skin care, and health care, but their quality and yield can be threatened by diseases, pearl nuclei transplantation rejection, and other external factors. The present study investigated the immune function of the tumor necrosis factor receptor (TNFR) gene in P. f. martensii to better understand immune responses related to nuclei rejection. The PmTNFR16 cDNA sequence obtained from cloning was 1675 bp in length and encoded 406 amino acid residues. Sequence analysis revealed that PmTNFR16 comprises one signal peptide domain, four TNFR domains, one transmembrane domain, and one death domain. Expression analysis revealed PmTNFR16 was highly expressed in the mantle and significantly up-regulated after exogenous stimuli. The effects of PmTNFR16 on immune effector molecules within the NF-κB signaling pathway were further explored using RNA interference probes for PmTNFR16. Pre-treatment of pearl oysters with dsRNA-PmTNFR before nucleus-insertion resulted in decreased expression of PmTNFR16 by 53 % at 24 h (p<0.01). Similarly, the expression of the NF-κB signaling pathway immune-related genes TRAF2, TRADD, IKK, NIK, and NF-κB significantly decreased at 24 h. The results indicated that PmTNFR16 was successfully silenced as were the expression of immune-related genes in the downstream NF-κB signaling pathway. Overall, these results indicate that PmTNFR16 may be involved in the immune response of the host organism by mediating the NF-κB signaling pathway. These observations provide a framework for future studies of the immune mechanisms of pearl oysters.