Immunoglobulins genes in Neoceratodus forsteri and Protopterus annectens explain the origin of the immunoglobulins of the animals that passed ashore

Abstract

AbstractSarcopterygii fish have great evolutionary interest since tetrapods and animals that came ashore arose from them. Within immunology, they can teach us about the emergence of Immunoglobulins D, A/X, and Y already present in amphibians. We have studied the genes of the immunoglobulins in the fish Sarcopterygii Neoceratodus forsteri and Protopterus annectens. In the first fish, we find that several loci for the constant chains of immunoglobulins are distributed in 4 chromosomes. We have found four genes for IgM, a gene for IgW and a gene for IgN. In the second, we find one locus with genes for IgN and IgM and another with one gene for IgW. With these sequences, together with those obtained in other publications, we have been able to study the possible evolution and emergence of immunoglobulin classes. We conclude that there are two evolutionary lines, one focused on IgM and very conservative, and the other focused on IgW, which allows high variability. The W line gave rise to the IgD of 11 domains of reptiles. IgA and IgY are unique since they arose from recombination between the two evolutionary lines. The W line gave origin to the CH1 and CH2 domains, and the M line gave the CH3 and CH4 domains.