Cloning and Gene Expression of a cDNA for the Chicken Follicle-Stimulating Hormone (FSH)-β-Subunit

Abstract

Follicle-stimulating hormone (FSH) is a member of pituitary glycoprotein hormones that are composed of two dissimilar subunits, α and β. Very little information is available regarding the nucleotide and amino acid sequence of FSH-β in avian species. For better understanding of the phylogenic diversity and evolution of FSH molecule, we have isolated and sequenced the complete complementary DNA (cDNA) encoding chicken FSH-β precursor molecule by reverse transcription–polymerase chain reaction (RT-PCR) and rapid amplification of cDNA end (RACE) methods. The cloned chicken FSH-β cDNA consists of 2457-bp nucleotides, including 44-bp nucleotides of the 5′-untranslated region (UTR), 396 bp of the open reading frame, and an extraordinarily long 3′-UTR of 2001-bp nucleotides followed by a poly(A)(16) tail. It encodes a 131-amino-acid precursor molecule of FSH-β-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 chicken FSH-β-subunit. Four proline residues, presumably responsible for changing the backbone direction of protein structure, are conserved in chicken FSH-β-subunit as well. The nucleotide sequence of chicken FSH-β cDNA shows high homology with quail FSH-β cDNA, 97% homology in the open reading frame, and 85% homology in the 3′-UTR. The deduced amino acid sequence of chicken FSH-β-subunit shows a remarkable similarity to other avian FSH-β-subunits, 98% homology with quail, and 93% homology with ostrich, whereas a lower similarity (66 to 70%) is noted when compared with mammalian FSH-β-subunits. By contrast, when comparing with the β-subunits of chicken luteinizing hormone and thyroid-stimulating hormone, the homologies are as low as 37 and 40%, respectively. FSH-β mRNA was only expressed in pituitary gland out of various tissues examined and can be up-regulated by gonadotropin-releasing hormone in pituitary tissue culture as estimated by real-time quantitative PCR.