Molecular cloning of inhibin/activin beta A-subunit complementary deoxyribonucleic acid and expression of inhibin/activin alpha- and beta A-subunits in the domestic hen.

A chicken inhibin/activin beta A-subunit cDNA clone has been isolated and used to detect the beta A-subunit mRNA in the hen. A cDNA library of the hen granulosa layer was screened with a rat inhibin beta A-subunit cDNA probe, and a cDNA of 1540 bp was cloned and sequenced. The clone contains the entire open reading frame of 1272 nucleotides encoding 424 amino acids. It shows 78% nucleotide identity (85% in deduced amino acids) in the full-length coding region and 85% nucleotide identity (98% in deduced amino acids) in the 116-amino acid C-terminal mature region to the rat beta A-subunit cDNA clone. The predicted positions of one N-linked glycosylation site and all cysteine residues are fully conserved as well. Northern blot analysis showed that the major 8.4-kb inhibin/activin beta A-mRNA band was primarily expressed in the granulosa layer of the preovulatory follicles. It was also detected in much less abundance in the theca layer, thyroid gland, heart, muscle, intestine, adrenal gland, liver, lung, spinal cord, and spleen. When a chicken inhibin alpha-subunit cDNA probe was used, the 1.7-kb major band of the inhibin alpha-subunit mRNA was detected most strongly in the granulosa layer and less abundantly in the postovulatory follicle, theca layer, testis, heart, and adrenal gland. Moreover, a distinct 1.3-kb alpha-mRNA was detected in the muscle and lung. The present cloning study extends our understanding of the inhibin/activin beta A-subunit cDNA from studied species to the chicken and shows that the beta A-subunit is highly conserved during evolution. Our data indicate that the mRNAs for inhibin/activin alpha- and beta A-subunits are widely present in a variety of chicken tissues but that the granulosa layer of large preovulatory follicles is the primary site of expression. The present study also suggests that both inhibin and activin may serve as local factors to regulate cell function in chicken tissues.