Comparative Analysis of the pIgR Gene from the Antarctic Teleost Trematomus bernacchii Reveals Distinctive Features of Cold Adapted Notothenioidei

The IgM and IgT classes were previously identified and characterized in the Antarctic teleost Trematomus bernacchii, a species belonging to the Perciform suborder Notothenoidei. Herein we characterized the gene encoding the polymeric immunoglobulin receptor (pIgR) in the same species and compared it to pIgR of multiple teleost species belonging to five perciform sub-orders, including 11 Antarctic and one non-Antarctic (Cottoperca gobio) notothenioid species, the latter living in less cold periantarctic sea. Antarctic pIgR genes displayed particularly long in-trons marked by sites of transposable elements and transcription factors. Furthermore, analysis of T. bernacchii pIgR cDNA unveiled multiple amino acid substitutions unique to Antarctic species, all introducing adaptive features, including N-glycosylation sequons. Interestingly, C. gobio shared most features with the other perciforms rather than with the cold adapted relatives. T. bernacchii pIgR transcripts were predominantly expressed in mucosal tissues, as indicated by q-PCR and in situ hybridization analysis. These results suggest that in cold adapted species pIgR preserved its fundamental role in mucosal immune defense, although remarkable gene structure modifications occurred.