Molecular Cloning and Sequence Analysis of the cDNAs for Pituitary Glycoprotein Hormone α Subunits from Two Species of Synbranchiformes, Monopterus albus and Ophisternon bengalense

Abstract

No information is available regarding the cDNA nucleotide and protein sequences of pituitary glycoprotein hormone α subunits (PGH α) from fish of the order Synbranchiformes. For better understanding of phylogenetic diversity and evolution of PGH α in fish, we have cloned cDNAs for PGH α subunits from swamp eels, Monopterus albus and Ophisternon bengalense, two members of the order Synbranchiformes, suborder Synbranchoidei, family Synbranchidae. The PGH α subunit cDNA was cloned by reverse transcription and polymerase chain reaction amplification from total pituitary RNA. The full length PGH α cDNA was obtained using 5′- and 3′- rapid amplification of cDNA ends (RACE). The PGH α 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 α 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 α 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 α 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%).