STUDIES ON THE STRUCTURE OF THE CONTROL REGION OF THE BAGRIDAE IN CHINA AND ITS PHYLOGENTIC SIGNIFICANCE

Bagridae belonging to Siluriformes, is a group of fishes widely distributed in China. The phylogenetic relationships of the species in this family are not fully identified and most of the previous works were based on external and osteological characteristics. Complete sequence of the mitochondrial DNA control region of the typical species of Family Bagridae were obtained by PCR and the structure of the control region was analyzed. The vertebrate mitochondrial control region is commonly subdivided into three domains that different from each other in base cmposition as well as in rate and mode of evolution. The central domain, containing the heavy strand's origin of replication is relatively conserved and characterized by a high GC content served domain; the ETAS(extended termination associated sequence) domain that usually has one or copies of termination associated sequences and that signals termination of the d-loop strands, and the CSB domain that are believed to function in its initiation. Nucleotide sequences of mitochondrial DNA control region were aligned with the Clustal X and MEGALIGN, then refined manually. Choosing A. sinensis and G. trilineatus as the outgroup, the phylogenetic trees were constructed with MEGA 2.1 by the neighbour-joining method and maximum-parsimony method based on the complete sequence of the control region. And the result is compared based on the topology and the bootstrap value. The average base composition is A:31.1% T:31.2% C:23.3 G14.3%. The base composition has bias against G, which is also the characteristic of mitochondrial DNA. And the A+T content is much higher than that of C+G. The mitochondrial DNA control region of Bagridae can also be divided into central domain, ETAS domain and CSB domain, which is in accordance with the basic structure shown in other species. Central domain, ETAS domain and CSB domain as well as some conserved sequences were identified in Bagridae and compared with other species. The phylogenetic studies based on neighbour-joining method and maximum-parsimony method are consistent. Family Bagridae forms a monophyletic group, and there is strong evidence that Pseudobagrus tenuis is grouped with Leiocassis crassilabris. It can be concluded that the control region can be used for the phylogenetic analysis; Family Bagridae forms a monophyletic group; P. tenuis should be transferred to the genus Leiocassis.