Analysis of the cathelicidin 1 gene locus in Atlantic cod (Gadus morhua).

Cathelicidins are one of the major families of antimicrobial peptides produced as part of the innate immune responses. We have studied the gene locus of the Atlantic cod cathelicidin gene (gmCath1) by sequencing of a BAC clone. Results have revealed the genes upstream and downstream of gmCath1 in a sequence of >92.6 kb and these include APG-9, obscurin, guanylate kinase and MMTA-2. There appears to be no pattern of synteny observed when the loci of cathelicidin genes in other species was analysed. Analysis of the promoter region of 1 kb upstream of the translation start codon led to the identification of numerous different putative transcription factor binding sites (TFBS) that are believed to be important for the control of immune gene expression. Further studies into the quantitative expression of gmCath1 found that it is constitutively expressed in the head kidney and spleen and significant increases in expression are observed at 24 h post injection with the immunostimulant ergosan. By inserting a 311 bp fragment of the gmCath1 promoter into a luciferase reporter vector we found that stimulation with Poly I:C results in significant up-regulation of gene expression. This report detailing the promoter region of a cathelicidin gene in teleost fish, and the varied putative TFBS identified, suggests that the gmCath1 gene is highly likely to be induced in response to a wide range of different immune stimuli including bacteria and viruses.