Cytosolic sensor genes against viral infection of rock bream Oplegnathus fasciatus

The defense system of a host body is initiated from recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs). Cytosolic PRRs detect especially microbial and host nucleic acid in the cytoplasm. Stimulator of interferon genes (STING), known as an endoplasmic reticulum adaptor, directly recognizes cyclic dinucleotides (CDNs) which are bacterial second messenger molecules and also controls an antiviral pathway in response to cytosolic DNA. Interferon (IFN)-induced protein with tetratricopeptide repeats (IFITs) family is a kind of IFN-stimulated genes and concerned in response to viral infection. In this study, we have characterized STING and IFIT5-like from rock bream, which is a famous species in Korea, at the molecular level and analyzed the transcriptional expression pattern on the viral challenges.

STING and IFIT homolog were identified from the rock bream cDNA and genomic database and designated as RbSTING and RbIFIT5. These cDNA sequences were analyzed about the putative coding region and its corresponding amino acid sequences. Pairwise sequence and multiple sequence alignments were carried out for sequence comparisons. To study of the transcriptional expression, tissues were collected from healthy and challenged tissues. Total RNA extraction and cDNA synthesis were performed. qPCR was used to determine the transcriptional expression pattern.

The RbSTING cDNA sequence was a 1242 bp that encoded 413 amino acid residues. The RbIFIT5 was confirmed as a 1434 bp sequence that encoded 478 amino acid residues. The tissue distribution analysis of these genes was determined by qRT-PCR of healthy rock bream. The expression level was normalized by β-actin expression value. Relative mRNA expression levels were calculated based on the expression in muscle. RbSTING expression was higher in gill and blood, intestine. Similarly, RbIFIT5 was higher in blood and heart, gill. In order to understand expression pattern of these genes at the viral infection, rock bream were challenged by either poly I:C and rock bream iridovirus (RBIV) and then blood, liver, spleen, and head kidney were isolated at different time points. RbSTING and RbIFIT5 expressions were up-regulated by poly I:C and RBIV. According to the results, RbSTING and RbIFIT5 are concerned to antiviral defense system.