IgH loci of American alligator and saltwater crocodile shed light on IgA evolution

Abstract

Immunoglobulin loci of two representatives of the order Crocodylia were studied from full genome sequences. Both Alligator mississippiensis and Crocodylus porosus have 13 genes for the heavy chain constant regions of immunoglobulins. The IGHC locus contains genes encoding four immunoglobulins M (IgM), one immunoglobulin D (IgD), three immunoglobulins A (IgA), three immunoglobulins Y (IgY), and two immunoglobulins D2 (IgD2). IgA and IgD2 genes were found in reverse transcriptional orientation compared to the other Ig genes. The IGHD gene contains 11 exons, four of which containing stop codons or sequence alterations. As described in other reptiles, the IgD2 is a chimeric Ig with IgA- and IgD-related domains. This work clarifies the origin of bird IgA and its evolutionary relationship with amphibian immunoglobulin X (IgX) as well as their links with mammalian IgA.

Mucosal Immunoglobulins

“…Although IgA appears to be lacking in Testudines (e.g., turtles) and Squamata such as snakes and lizards, IgA antibodies have been described in crocodilians (e.g., alligators and crocodiles) (Cheng et al, 2013;Magadan-Mompo et al, 2013a). Crocodilians have three IgA genes that are arranged in reverse orientation to the other Ig genes, as in birds.…”

“…The primary amino acid structures of α chains of human (both subclasses and allotypes), gorilla, chimpanzee, orangutan, gibbon, macaque, sooty mangabey, dog, pig, goat, sheep, horse, dolphin, bat, rabbit, mouse, rat, cow, possum, duckbill platypus, echnida, quail, pheasant, turkey, chicken, duck, goose, ostrich, alligator, and crocodile IgA have been obtained by amino acid and/or DNA sequence analyses, and IgA-like antibodies have been identified in leopard geckos Burnett et al, 1989;Kawamura et al, 1991Kawamura et al, , 1992Patel et al, 1995;Brown and Butler, 1994;Knight et al, 1984;Kratzin et al, 1975;Mansikka, 1992;Putnam et al, 1979;Torano and Putnam, 1978;Tsuzukida et al, 1979;Tucker et al, 1981;Yang et al, 1979;Brown et al, 1997;Belov et al, 2002;Lundquist et al, 2001;Wagner et al, 2003;White et al, 1998;Zhou et al, 2005Zhou et al, , 2006Scinicariello et al, 2006;Mancia et al, 2007;Deza et al, 2007;Choi et al, 2010;Vernersson et al, 2010;Butler et al, 2011;Huang et al, 2012;Guo et al, 2014;Cheng et al, 2013;Magadan-Mompo et al, 2013a). Aligned sequences of IgA from selected species are shown in Figure 3.…”

Biophysical and Biochemical Characterization of Avian Secretory Component Provides Structural Insights into the Evolution of the Polymeric Ig Receptor

“…In amphibians, the pIgR ectodomain contains four Ig-like domains (D1-D4) that bind polymeric forms of IgM and IgX, an amphibian mucosal antibody (10). Similar to amphibians, avian and reptilian pIgR also contain four extracellular domains, but bind to polymeric forms of IgM and IgA (pIgA), which assemble together with a protein called joining (J) chain (5,7,11). Mammalian SC also bind pIgs, typically dimeric IgA (dIgA) and pentameric IgM (pIgM), however a gene duplication event added a domain immediately following D1, enlarging mammalian SC to five Ig-like domains (D1-D5) (5,6).…”

Intraclass diversification of immunoglobulin heavy chain genes in the African lungfish

“…Currently, we do not know what these are for IgN and IgQ, but they appear to be present in Dipnoi only. The current dogma regarding the evolution of IgY, IgA(X) postulates that IgA(X) is an IgY/IgM chimera, and thus IgY may have emerged earlier than IgA(X) (Magadán-Mompó et al 2013; Mashoof et al 2013). …”