Two types of cDNA, each encoding a different β-subunit of striped bass (Morone saxatilis, Teleostei) gonadotrophins (GTH-Iβ and GTH-IIβ), as well as the glycoprotein α-subunit, were cloned by screening a striped bass pituitary cDNA library. The probes used for screening the library were cloned cDNA fragments, generated by PCR amplification of reverse-transcribed mRNA obtained from two pituitaries. The nucleotide sequences of the α-subunit, GTH-Iβ and GTH-IIβ are 626, 524 and 580 bases long, encoding peptides of 117, 120 and 147 amino acids respectively. Striped bass GTH-Iβ and GTH-IIβ share a sequence identity of 48% at the nucleic acid level, and 30% at the amino acid level. A cluster analysis of vertebrate pituitary glycoprotein β-subunits suggests that teleost GTH-IIβ is more closely related to tetrapod LH than to FSH. Administration of gonadotrophin-releasing hormone analogue ([d-Ala6,Pro9Net]-LHRH) to juvenile striped bass resulted in ten-, two- and fivefold increases in the expression of the α-subunit, GTH-Iβ and GTH-IIβ respectively. These results suggest that each of the GTH subunits is differentially regulated, and further corroborate the functional duality of teleost gonadotrophins.
The nucleotide sequences of the α-subunit, GTH-Iβ and GTH-IIβ reported in this paper have been deposited in the GenEMBL database with the respective accession numbers L35071, L35070 and L35096.