Three IgH isotypes, IgM, IgA and IgY are expressed in Gentoo penguin and zebra finch

<div><p>Previous studies on a limited number of birds suggested that the IgD-encoding gene was absent in birds. However, one of our recent studies showed that the gene was definitely expressed in the ostrich and emu. Interestingly, we also identified subclass diversification of IgM and IgY in these two birds. To better understand immunoglobulin genes in birds, in this study, we analyzed the immunoglobulin heavy chain genes in the zebra finch (<i>Taeniopygia guttata</i>) and Gentoo penguin (<i>Pygoscelis papua</i>), belonging respectively to the order Passeriformes, the most successful bird order in terms of species diversity and numbers, and Sphenisciformes, a relatively primitive avian order. Similar to the results obtained in chickens and ducks, only three genes encoding immunoglobulin heavy chain isotypes, IgM, IgA and IgY, were identified in both species. Besides, we detected a transcript encoding a short membrane-bound IgA lacking the last two CH exons in the Gentoo penguin. We did not find any evidence supporting the presence of IgD gene or subclass diversification of IgM/IgY in penguin or zebra finch. The obtained data in our study provide more insights into the immunoglobulin heavy chain genes in birds and may help to better understand the evolution of immunoglobulin genes in tetrapods.</p></div

A Comprehensive Analysis of the Phylogeny, Genomic Organization and Expression of Immunoglobulin Light Chain Genes in <i>Alligator sinensis</i>, an Endangered Reptile Species

<div><p>Crocodilians are evolutionarily distinct reptiles that are distantly related to lizards and are thought to be the closest relatives of birds. Compared with birds and mammals, few studies have investigated the Ig light chain of crocodilians. Here, employing an <i>Alligator sinensis</i> genomic bacterial artificial chromosome (BAC) library and available genome data, we characterized the genomic organization of the <i>Alligator sinensis</i> IgL gene loci. The <i>Alligator sinensis</i> has two IgL isotypes, λ and κ, the same as <i>Anolis carolinensis</i>. The Igλ locus contains 6 C_λ genes, each preceded by a J_λ gene, and 86 potentially functional V_λ genes upstream of (J_λ-C_λ)_n. The Igκ locus contains a single C_κ gene, 6 J_κs and 62 functional V_κs. All V_L genes are classified into a total of 31 families: 19 V_λ families and 12 V_κ families. Based on an analysis of the chromosomal location of the light chain genes among mammals, birds, lizards and frogs, the data further confirm that there are two IgL isotypes in the <i>Alligator sinensis</i>: Igλ and Igκ. By analyzing the cloned Igλ/κ cDNA, we identified a biased usage pattern of V families in the expressed V_λ and V_κ. An analysis of the junctions of the recombined VJ revealed the presence of N and P nucleotides in both expressed λ and κ sequences. Phylogenetic analysis of the V genes revealed V families shared by mammals, birds, reptiles and <i>Xenopus</i>, suggesting that these conserved V families are orthologous and have been retained during the evolution of IgL. Our data suggest that the <i>Alligator sinensis</i> IgL gene repertoire is highly diverse and complex and provide insight into immunoglobulin gene evolution in vertebrates.</p></div