Discovery of an unusual alternative splicing pathway of the immunoglobulin heavy chain in a teleost fish, Danio rerio

In present study, we identified a novel membrane immunoglobulin M isotype from zebrafish (Danio rerio), which was designated as mIgM-2, adding a new member to the Immunoglobulin family in teleost fish. The full length of cloned mIgM-2 cDNA was 611 bp, encoding 150 amino acids. The putative mIgM-2 protein sequence consists of one constant region and a trans-membrane region. Phylogenetic analysis showed that mIgM-2 grouped with the known zebrafish IgM sequences. The mIgM-2 mRNA was widely expressed in immune-related tissues including intestine, kidney and skin. In vivo stimulation with LPS significantly up-regulates the expression of mIgM-2. Our results will add new insight into the immunoglobulin class diversity of teleost fish, and to better understand the evolutionary history of adaptive immunity from fish to mammals as a whole.