Abstract:This study aimed to explore the pathogenic mechanism of the iridescent virus and provide the theory basis for clinical diagnosis and treatment in Epinephelus lanceolatus. The full-length E. lanceolatus interferon-stimulated gene 15 (isg15) was obtained by PCR and rapid amplification of cDNA ends (RACE). The full-length cDNA of isg15 was 910 bp, including an open reading frame (ORF) of 468 bp, which encoded a polypeptide of 155 amino acids. The molecular mass of the deduced amino acid sequence was 17.09 kDa, with an estimated pI of 9.33. Conserved domain analysis revealed that the isg15 protein of E. lanceolatus contained two ubiquitin-like domains, and the C-terminal had a highly conserved motif of "Leu Arg Leu Arg Gly Gly (LRLRGG)". Sequence and phylogenetic analyses showed that the amino acid sequence of isg15 in E. lanceolatus had the closest identity to Epinephelus coioides, with a similarity of approximately 88.24%. In addition, the homologous similarity of the E. lanceolatus isg15 with Scophthalmus maximus and Larimichthys crocea was 61.18% and 60.59%, respectively. Real-time quantitative PCR was used to detect the expression patterns of the isg15 gene in the healthy tissues of E. lanceolatus and the changes in the spleen and kidney at different times after infection with the iridovirus. The results showed that the isg15 gene was mainly expressed in the blood of E. lanceolatus and was highly expressed in various immune-related tissues, such as the liver and kidney. Upon induction with iridovirus, isg15 gene expression was up-regulated in the kidney and spleen, and reached a peak at 72 h, indicating that isg15 may play an important role in the immune response of E. lanceolatus against viral infection. In this study, the analyses and expression patterns of isg15 in E. lanceolatus were studied, which is helpful to further understand the antiviral regulatory mechanism of isg15 in teleosts, and provides a theoretical basis for the disease-resistant molecular breeding of E. lanceolatus.
