Pituitary Glycoprotein Hormone β Subunits in the Australian Lungfish and Estimation of the Relative Evolution Rate of These Subunits Within Vertebrates1

Abstract

The beta subunits of the two pituitary gonadotropins LH and FSH and of thyroid-stimulating hormone (TSH) were cloned from Australian lungfish (Neoceratodus forsteri) pituitary glands. These three glycoprotein hormone beta subunits possess the main characteristics common to their counterparts in other vertebrates. Taking advantage of the phylogenetic position of the lungfish, close to the root of tetrapods, a maximum parsimony tree was inferred from these new sequences and sequences from representatives of the diversity of vertebrates. The topology of the tree was imposed so that it reflected as closely as possible the real evolutionary history of the subunits. This tree was used to estimate the relative evolution rate of the three subunits in vertebrates. Cumulated amino acid substitutions from the basal subunit node (ancestral subunit sequence) to the species node were calculated and compared. It showed that a burst in evolutionary rate occurred for the LHbeta subunit in the tetrapod lineage sometime after the emergence of amphibians. The rate of evolution of the LHbeta subunit was particularly high throughout the radiation of mammals while FSH and TSHbeta subunits kept quite stable in this lineage. A burst in evolutionary rate was also observed for the FSHbeta subunit in the lineage leading to teleosts sometime after the emergence of chondrosteans and the dynamic of evolution was high throughout the radiation of teleosts. These results were consistent with data obtained from pairwise comparisons.

Gonadotropin-like and adrenocorticotropin-like cells in the pituitary gland of hagfish, Paramyxine atami; immunohistochemistry in combination with lectin histochemistry

“…These glycoprotein hormones are believed to have evolved from a common ancestral molecule through duplication of the β-subunit genes and subsequent divergence (Dayhoff 1976;Kawauchi and Sower 2006). Two GTHs have been identified in all taxonomic groups of gnathostomes, including actinopterygians (Suzuki et al 1988;Querat et al 2000), sarcopterygians (Querat et al 2004), and chondrichthyans (Querat et al 2001), but not in jawless vertebrates (agnathans). A single GTHβ-like protein has recently been identified in sea lampreys by cDNA cloning .…”

Receptor-selective determinants in catfish gonadotropin seat-belt loops

“…lungfishes and tetrapods) approximately 400 million years ago (Hedges and Kumar, 2003). Although phylogenetic analysis clusters all FSH, LH, and TSH ␤-subunit orthologs in separate branches (Vischer et al, 2003c;Quérat et al, 2004), striking differences are present between orthologous ␤-subunits when looking at their seat-belt loops (Fig. 3).…”

The hagfish heart

“…These glycoprotein hormones (GPH) are believed to have evolved from a common ancestral molecule through duplication of β-subunit genes and subsequent divergence (27,28). Two GTHs have been identified in all taxonomic groups of gnathostomes, including actinopterygians (29,30), sarcopterygians (31), and chondrichthyans (32), but not in agnathans.…”