Molecular cloning of the cDNA encoding follicle-stimulating hormone β subunit of the Chinese soft-shell turtle Pelodiscus sinensis, and its gene expression

Follicle-stimulating hormone (FSH) is a member of the pituitary glycoprotein hormone family. These hormones are composed of two dissimilar subunits, α and β. Very little information is available regarding the nucleotide and amino acid sequence of FSHβ in reptilian species. For better understanding of the phylogenetic diversity and evolution of FSH molecule, we have isolated and sequenced the complementary DNA (cDNA) encoding the Chinese soft-shell turtle (Pelodiscus sinensis, Family of Trionychidae) FSHβ precursor molecule by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA end (RACE) methods. The cloned Chinese soft-shell turtle FSHβ cDNA consists of 602-bp nucleotides, including 34-bp nucleotides of the 5′-untranslated region (UTR), 396-bp of the open reading frame, and 3′-UTR of 206-bp nucleotides. It encodes a 131-amino acid precursor molecule of FSHβ subunit with a signal peptide of 20 amino acids followed by a mature protein of 111 amino acids. Twelve cysteine residues, forming six disulfide bonds within β-subunit and two putative asparagine-linked glycosylation sites, are also conserved in the Chinese soft-shell turtle FSHβ subunit. The deduced amino acid sequence of the Chinese soft-shell turtle FSHβ shares identities of 97% with Reeves’s turtle (Family of Bataguridae), 83–89% with birds, 61–70% with mammals, 63–66% with amphibians and 40–58% with fish. By contrast, when comparing the FSHβ with the β-subunits of the Chinese soft-shell turtle luteinizing hormone and thyroid stimulating hormone, the homologies are as low as 38 and 39%, respectively. A phylogenetic tree including reptilian species of FSHβ subunits, is presented for the first time. Out of various tissues examined, FSHβ mRNA was only expressed in the pituitary gland and can be up-regulated by gonadotropin-releasing hormone in pituitary tissue culture as estimated by fluorescence real-time PCR analysis.