Immunoglobulin genes of the turtles.

The availability of reptile genomes for the use of the scientific community is an exceptional opportunity to study the evolution of immunoglobulin genes. The genome of Chrysemys picta bellii and Pelodiscus sinensis is the first one that has been reported for turtles. The scanning for immunoglobulin genes resulted in the presence of a complex locus for the immunoglobulin heavy chain (IGH). This IGH locus in both turtles contains genes for 13 isotypes in C. picta bellii and 17 in P. sinensis. These correspond with one immunoglobulin M, one immunoglobulin D, several immunoglobulins Y (six in C. picta bellii and eight in P. sinensis), and several immunoglobulins that are similar to immunoglobulin D2 (five in C. picta belli and seven in P. sinensis) that was previously described in Eublepharis macularius. It is worthy to note that IGHD2 are placed in an inverted transcriptional orientation and present sequences for two immunoglobulin domains that are similar to bird IgA domains. Furthermore, its phylogenetic analysis allows us to consider about the presence of IGHA gene in a primitive reptile, so we would be dealing with the memory of the gene that originated from the bird IGHA. In summary, we provide a clear picture of the immunoglobulins present in a turtle, whose analysis supports the idea that turtles emerged from the evolutionary line from the differentiation of birds and the presence of the IGHA gene present in a common ancestor.

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

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.

Immunoglobulin light chains in medaka (Oryzias latipes).

The gene segments encoding antibodies have been studied in many capacities and represent some of the best-characterized gene families in traditional animal disease models (mice and humans). To date, multiple immunoglobulin light chain (IgL) isotypes have been found in vertebrates and it is unclear as to which isotypes might be more primordial in nature. Sequence data emerging from an array of fish genome projects is a valuable resource for discerning complex multigene assemblages in this critical branch point of vertebrate phylogeny. Herein, we have analyzed the genomic organization of medaka (Oryzias latipes) IgL gene segments based on recently released genome data. The medaka IgL locus located on chromosome 11 contains at least three clusters of IgL gene segments comprised of multiple gene assemblages of the kappa light chain isotype. These data suggest that medaka IgL gene segments may undergo both intra- and inter-cluster rearrangements as a means to generate additional diversity. Alignments of expressed sequence tags to concordant gene segments which revealed each of the three IgL clusters are expressed. Collectively, these data provide a genomic framework for IgL genes in medaka and indicate that Ig diversity in this species is achieved from at least three distinct chromosomal regions.

Immunoglobulin heavy chains in medaka (Oryzias latipes).

BACKGROUND: Bony fish present an immunological system, which evolved independently from those of animals that migrated to land 400 million years ago. The publication of whole genome sequences and the availability of several cDNA libraries for medaka (Oryzias latipes) permitted us to perform a thorough analysis of immunoglobulin heavy chains present in this teleost. RESULTS: We identified IgM and IgD coding ESTs, mainly in spleen, kidney and gills using published cDNA libraries but we did not find any sequence that coded for IgT or other heavy chain isotypes described in fish. The IgM - ESTs corresponded with the secreted and membrane forms and surprisingly, the latter form only presented two constant heavy chain domains. This is the first time that this short form of membrane IgM is described in a teleost. It is different from that identified in Notothenioid teleost because it does not present the typical splicing pattern of membrane IgM. The identified IgD-ESTs only present membrane transcripts, with Cµ1 and five Cδ exons. Furthermore, there are ESTs with sequences that do not have any VH which disrupt open reading frames. A scan of the medaka genome using transcripts and genomic short reads resulted in five zones within a region on chromosome 8 with Cµ and Cδ exons. Some of these exons do not form part of antibodies and were at times interspersed, suggesting a recombination process between zones. An analysis of the ESTs confirmed that no antibodies are expressed from zone 3. CONCLUSIONS: Our results suggest that the IGH locus duplication is very common among teleosts, wherein the existence of a recombination process explains the sequence homology between them.

Snakes antibodies.

Immunoglobulins are basic molecules of the immune system of vertebrates. In previous studies we described the immunoglobulins found in two squamata reptiles, Anolis carolinensis and Eublepharis macularius. Snakes are squamata reptiles too but they have undergone an extreme evolutionary process. We therefore wanted to know how these changes affected their immunoglobulin coding genes. To perform this analysis we studied five snake transcriptomes and two genome draft sequences. Sequences coding for immunoglobulin M (IgM), immunoglobulin D (IgD) and two classes of immunoglobulin Y (IgY - named IgYa and IgYb-) were found in all of them. Moreover, the Thamnophis elegans transcriptome and Python molurus genome draft sequences showed a third class of IgY, the IgYc, whose constant region only presents three domains and lacks the CH2. All data suggest that the IgYb is the evolutionary origin of this IgYc. An exhaustive search of the light chains were carried out, being lambda the only light chain found in snakes. The results provide a clear picture of the immunoglobulins present in the suborder Serpentes.

Presence of an unique IgT on the IGH locus in three-spined stickleback fish (Gasterosteus aculeatus) and the very recent generation of a repertoire of VH genes.

This study describes the IGH locus in Gasterosteus aculeatus, with 10 genes encoding three immunoglobulin classes: IgT, IgM and IgD. These genes are organized into a structure with three repeats of IGHT-IGHM-IGHD separated by segments including the VH segments. There was also a fourth IGHT gene. IGHT encodes an antibody with three immunoglobulin domains. Comparative studies indicate it is related to IgT and IgZ and other antibodies located upstream of the IGHM in teleost fish. The IGHM and IGHD are similar to the ones described in teleost. The IGHM has four immunoglobulin domains while the IGHD seven and none is duplicated. The IGH locus of G. aculeatus has 49 VH segments located in four regions. They belonged to four families, whose members show a greater than 92% amino acid identity, indicating that VH families diversified recently. Phylogenetic reconstruction suggests they were originated from four VH segments that must have duplicated with the constant region genes, after that the four VH segments gave rise to the remaining segments. This suggests the presence of an active biological process that generates diversity in VH regions.

The immunoglobulin heavy chain locus in the reptile Anolis carolinensis.

We describe the entire immunoglobulin heavy chain (IgH) locus from the reptile Anolis carolinensis. The heavy chain constant (C(H)) region includes C mu, C delta and C upsilon genes. This is the first description of a C upsilon gene in the reptilian class. Variable (V(H)), diversity (D(H)) and joining (J(H)) genes are located 5' from the constant (C(H)) chain complex locus. The C mu and C upsilon genes encode antibodies with four immunoglobulin domains. The C delta gene encoded an 11 domain delta heavy chain as in Eublepharis macularius. Seventy V(H) genes, belonging to 28 families, were identified, and they can be sorted into five broader groups. The similarity of the organization of the reptilian genes with those of amphibians and mammals suggests the existence of a process of heavy chain genomic reorganization before the radiation of tetrapod vertebrates.