Immunoglobulin T genes in Neopterygii

Abstract

In teleost fishes there are three immunoglobulin isotypes named immunoglobulin M (IgM), D (IgD) and T (IgT). IgT has been the last to be described and is considered a teleosts-fish specific isotype. From the recent availability of genome sequences of fishes, an in-depth analysis of Actinopterygii immunoglobulin heavy chain genes was undertaken. With the aid of a bioinformatics pipeline, a machine learning software, CHfinder, was developed that identifies the coding exons of the CH domains of fish immunoglobulins. Using this pipeline, a high number of such sequences were obtained from teleosts and holostean fishes. IgT was found in teleost and holostean fishes that had not been previously described. A phylogenetic analysis reveals that IgT CH1 exons are similar to the IgM CH1. This analysis also demonstrates that the other three domains (CH2, CH3 and CH4) were not generated by recent duplication processes of IgM in Actinopterygii, indicating it is an immunoglobulin with an earlier origin.