A comprehensive evolutionary analysis based on nucleotide and amino acid sequences of the α- and β-subunits of glycoprotein hormone gene family

Abstract

On the basis of nucleotide sequences of the coding region and their predicted amino acid sequences, 58 glycoprotein hormone subunit genes were compared, aligned and used to construct phylogenetic trees for this family. The analysis included 17 α-subunits, eight TSHβ-, six FSHβ-, 17 LHββ/CGβ-, four fish gonadotropin (GTH)-Iβ-, five fish GTH-IIβ- and one additional fish GTHβ-subunits. The reliability of the phylogenetic trees was probed with the bootstrapping test. Our results indicated that: both the α- and β-subunits of the family diverged from a common ancestral gene about 927 million years ago; the initial precursor of the β-subunit duplicated to give rise to the LHβ and a second hormone, the latter then duplicating to FSHβ and TSHβ, so that FSHβ is related more to TSHβ than to LHβ; and bony fish GTH-Iβ is highly related to mammalian FSHβ, whereas the bony fish GTH-IIβ is more related to mammalian LHβ. For scientific consistency and convenience, we propose that the following nomenclature be adoted; all fish gonadotropins of type I be classified as FSH and all type II be classified as LH hormones. In addition, on the basis of results from this and other studies, we propose an evolutionary history for this glycoprotein hormone family. Reconstruction of the evolutionary history of this family would not only provide clues to understanding thyrotropin and gonadotropin functions, but would also allow further revision of the present nomenclature of the gonadotropins in fish.