Molecular cloning and sequence analysis of the cDNAs for pituitary glycoprotein hormone alpha subunits from two species of synbranchiformes, Monopterus albus and Ophisternon bengalense

摘要

No information is available regarding the cDNA nucleotide and protein sequences of pituitary glycoprotein hormone alpha subunits (PGH alpha) from fish of the order Synbranchiformes. For better understanding of phylogenetic diversity and evolution of PGH alpha in fish, we have cloned cDNAs for PGH alpha subunits from swamp eels, Monopterus albus and Ophisternon bengalense, two members of the order Synbranchiformes, suborder Synbranchoidei, family Synbranchidae. The PGH alpha subunit cDNA was cloned by reverse transcription and polymerase chain reaction amplification from total pituitary RNA. The full length PGH alpha cDNA was obtained using 5'- and 3'-rapid amplification of cDNA ends (RACE). The PGH alpha of these two species possessed 354 bp of coding region, which encoding a protein of 117 amino acids consisting of a putative signal peptide of 23 amino acids and a mature peptide of 94 amino acids. The amino acid sequence identity of PGH alpha between the two species is 93.8%. All 10 cysteine residues, forming 5 disulfide linkage, and 2 putative N-linked glycosylation sites are conserved in the PGH alpha subunits of the two species. Three proline residues, presumably responsible for changing the backbone directions of the protein structure, are conserved as well. Phylogenetic analysis of PGH alpha subunits based on their amino acid sequences revealed that the percent identities of the swamp eels are highest (92.5%) with fishes of Perciformes, intermediate with Pleuronectiformes (82.5%) and Cyprinodontiformes (72.2%), and lowest with Salmoniformes, Cypriniformes, Siluriformes, Anguilliformes, Acipenseriformes and Ceratodontiformes (56.7%-65.1%).