Abstract:This study aimed to investigate the transcriptional regulation of a teleost antimicrobial peptide. The expression pattern of the rainbow trout Cathelicidin2 (Cath2) gene was analyzed by quantitative real-time PCR (qRT-PCR). Cath2 was expressed in tissues closely related to immune defense, including the gill and head kidney, and expression significantly increased after both bacterial and viral infections. Promoter and transcription factor binding sites were analyzed for the upstream regulatory sequence of Cath2 gene. The predicted promoter contained characteristic eukaryotic TATA and CAAT boxes, as well as multiple binding sites for immune-related transcription factors, including two candidate binding sites for nuclear factor kappa B (NFκB) on the positive strand of the core promoter. In Ctenopharyngodon idella kidney cell lines, transcription of both green fluorescent protein and firefly luciferase genes was initiated by the predicted Cath2 promoter. Both the bacterial mimetic lipopolysaccharide and the viral mimetic polyinosinic polycytidylic acid up-regulated promoter activity. As shown in the dual luciferase reporter assay, promoter activity was enhanced by co-expression of the transcription factor NFκB, indicating that Cath2 is regulated by the NFκB pathway. These results suggest that expression of the rainbow trout Cath2 gene could be induced by different immune stimuli, and its promoter might serve as an immune-inducible transgenic element. The Cath2 promoter may initiate the transcription of heterologous immune genes against exogenous infection in a proper expression pattern, avoiding excessive transcription under unnecessary conditions; therefore, it has potential for genetic engineering approaches in the breeding of disease-resistant fish.
