Characterization and expression studies of Gaduscidin-1 and Gaduscidin-2; paralogous antimicrobial peptide-like transcripts from Atlantic cod (Gadus morhua)

Piscidins are a family of antimicrobial peptides (AMPs) from fish that constitute an important component of their innate immune system. Based on previously generated Atlantic cod (Gadus morhua) expressed sequence tags (ESTs), we identified sequences representing two paralogous AMP-like transcripts. These Atlantic cod paralogues were termed gaduscidins (GAD-1 and GAD-2), derived from the genus name Gadus. We obtained full-length cDNA sequences for these putative AMP-encoding transcripts using bi-directional rapid amplification of cDNA ends (RACE). GAD-1 and GAD-2 putative peptides exhibit sequence similarity with members of the piscidin family from teleost fish. Quantitative reverse transcription - polymerase chain reaction (QPCR) was utilized in transcript expression studies of GAD-1 and GAD-2. We examined the constitutive expression of these transcripts in six tissues (head kidney, blood, brain, gill, pyloric caecum, and spleen) of non-stressed juvenile cod; GAD-1 and GAD-2 transcripts were detected in all six tissues, with the highest expression of both transcripts being in spleen, head kidney, and gill. Transcript expression of GAD-1 and GAD-2 was also examined in immune tissues (spleen and head kidney) following intraperitoneal (IP) injection of formalin-killed, atypical Aeromonas salmonicida (ASAL) or phosphate-buffered saline (PBS control). Both transcripts were weakly (less than 4-fold) up-regulated by ASAL in spleen but non-responsive to ASAL in head kidney. Since GAD-1 and GAD-2 transcripts are highly expressed constitutively in immune-relevant tissues (e.g. spleen and head kidney), and are weakly induced in spleen following IP injection with bacterial antigens, they may represent important components of innate immunity in Atlantic cod.