The Research On The Immunoglobulin Heavy Chain Sequences Of Five Acipenseridae

Sturgeon, whose earliest fossils are found in strata from the Devonian Period (450-350 million years ago), belongs to Class Osteichthyes, Subclass Actinopterygii, Catalogue Chondrostei and Order Acipenseriformes. This large size living fossil fish has considerable economic and ecological importance. At present, there are 26 species of sturgeon worldwide, and most of wild ones are endangered species. Recently, many researchers dedicated themselves to rescuing and protecting the sturgeon resource.Sturgeon is placed in the evolutionary transition from Chondrichthyes to Osteichthyes, sharing many characteristics of the both, so it has much crucial theoretical meaning in developmental biology such as vertebrate evolution research. In molecular genetics level, the evolutionary differentiation of cartilaginous fishes and bony fishes is associated with a dramatic change of the organization and, probably, regulation of immunoglobulin genes. The study of sturgeon Ig serves as a valuable tool for analyzing the kinship of the Family Acipenseridae and the evolution of their immune system. In this paper, we obtained the Ig heavy chain variable region sequence from Amur sturgeon, Ig heavy chain constant region sequences from Amur sturgeon, Huso sturgeon, Russian sturgeon, Sterlte and Chinese sturgeon respectively, also analyzed them by some bioinformatics methods.We cloned Amur sturgeon IGH variable region alleles by RT-PCR using specific primers to investigate the IGH locus gene organization and the VH diversity. By bioinformatics analyzing, the VH regions, whose identities ranged from 75 to 99% with the leap peptide (LP) identities higher than 90%, belonged to the same family. We found many motifs in the D segment are conserved, whereas the CDR3 regions are not. Further, we deduced that there are at least 12 different JH segments contributing to the antibody variability repertoire of the sturgeon in the locus. Sturgeon, in addition to the random rearrangement of VH, D, and JH segments, has exonuclease activity and an introduction of N and probably P nucleotides at the site of rearrangement.Then we studied on the IGH constant region of Amur sturgeon, Russian sturgeon, Sterlte. Chinese sturgeon and Huso huso. As above, the aim genes were cloned by RT-PCR methods, and then the characteristics and functions of its conceptual amino acid sequences were determined. The IGH gene constant region contains four constant region domain-encoding exons (CH1-CH4), of which CH4 sub-regions one another were the most conserved and had the highest identity scores among all the experimental species. According to the phylogenetic tree, variation expectation value (Kaa), and CH4 sub-region species differentiation time (T)analysis, we found that Chinese sturgeon and the theoretical common ancestor of the other fiveform the first bifurcation of the tree, while, among the five left, Amur sturgeon and Huso sturgeon together, Russian sturgeon and Siberian sturgeon (data from GenBank) together, Sterlte itself form another three bifurcations respectively. This result can clearly explain the relations of taxonomic status, geographical distribution and evolution among the species studied.So far, there are few reports on sturgeon Ig in molecular biology level, especially none in China. Besides, no research on sequence alignment of IGH constant region among different kinds of fishes has been done. This work would provide a valuable basis for later related research in experimental data and theory. The sturgeon belongs to chonrdr-ganoid scale fish, sharing some characteristics with not only chondrichthyes but osteichthyes. In immunogenetics aspect, sturgeon more closely related to elasmobranches than to teleosts and higher vertebrates, is therefore an interesting group to study in terms of gene organization and diversifying mechanisms. So the studies on their immunoglobulins have a profound significance in phylogenesis offish immunity system.