The immunoglobulin gene loci in the teleost Gasterosteus aculeatus

In the present study, we have annotated both the immunoglobulin heavy (IgH) and light (IgL) chain genes in the stickleback (Gasterosteus aculeatus), based on the recently released genome data. The IgH gene locus is arranged in a configuration of (Vn-D-J-Cζ-D3-J4-Cμ-Cδ)3-V6-D-J-Cζ, which is structurally different from any of the known teleost IgH loci. The μ genes consistently exhibit a 4-CH encoding structure and all the ζ genes encode only three CH domains (lacking the equivalent exon of the zebrafish ζCH2). As in many other teleosts, the stickleback δ genes contain multiple CH exons, but exist as three copies. The members of four VH gene families, containing 47 segments, were interspersed in the germline. The stickleback IgL chain genes are also organized in multiple clusters and located in three chromosomes (10, 11, and 15). Sequence and phylogenetic analyses revealed that two isotypes, L1 (κ, including two subgroups, 1A and 1B) and L2 (σ) could be identified. The transcriptional orientations of the VL segments were found to be either the same (only in L2 isotype) or opposite to (in L1A, 1B and 2 isotypes) those of the JL and CL segments, indicating that these segments would undergo rearrangement by deletion or inversion when expressed.