cDNA cloning, phylogenetic analysis of two gonadotropins #beta# subunits sequences of Amur sturgeon

To elucidate the role of gonadotropin （GTH） in cultured amur sturgeon Acipenser schrenkii, we extracted total RNA from the pituitary gland and cloned two gonadotropin β-subunits using GeneRacer~(TM) technology. The cDNA of GTH Ⅰ-#beta# subunits is 1 088 bp, and the open reading frame 384 bp encoding peptides of 128 amino acid. The cDNA of GTHⅡ-#beta# is 616 bp and the open reading frame is 408 bp encoding 136 amino acid. They were submitted to GenBank, with accessions No. AY575920 （GTH Ⅰ-#beta#） and No. AY575921 （GTH Ⅱ-#beta#） respectively. Multiple amino acid sequences alignments were performed among vertebrates including teleostei, chondrostei, amphibian, tetrapod, avian and mammalian. The pairwise distances were computed and phylogenetic trees were constructed using NJ and MP methods based on the codon sequences （cds） of the chosen species by Mega 2 software. MP tree was also deduced from data of two subunits mature peptides. It showed that GTH Ⅰ-#beta# subunit of amur sturgeon has the highest homology with Siberian sturgeon, which was 99.1% similarity, and the lowest identity percent was 34.5 %, with the species of Perciformes. The high degree similarity of amur sturgeon GTHⅡ #beta#-subunit with Siberian sturgeon was 98.3 % ; it was more than 60 % similarity between chondrastei with teleostei except Perciformes, whereas the lowest similarity was with avian （42.8 % ）. The topology of two #beta# subunits phylogenetic trees deduced by NJ and MP methods were similar. The Chondrostei and Teleostei were at two distinct clades and formed the Osteichthyes which was in agree with traditional classification. The similarity, heredity distances and the branches length of each lineage showed that GTH Ⅰ -#beta# subunit had faster evolution rate in teleostei while LH #beta# was in the same as in Amniota. It was concluded that the evolution of these two glycoprotein #beta#-subunits were concomitant with the species evolution.