Molecular Cloning and Expression Analysis of the Complementary Deoxyribonucleic Acid for Chicken Inhibin/Activin bB Subunit1

Inhibins and activins are dimeric peptide hormones that play an integral role in the intraovarian regulation of folliculogenesis. The domestic hen, with its well-defined follicular hierarchy, pro-vides a unique model in which to study the role of these hor-mones in follicular development. In the present study, the com-plete coding sequence and deduced amino acid sequence for the chicken inhibin/activin bB subunit has been determined from cDNA clones isolated from a chicken ovarian granulosa cell li-brary. This bB-subunit cDNA predicts a precursor protein of 392 amino acids containing the mature C-terminal 115 amino acid bB subunit. When compared to the bB subunit isolated from a variety of species, the chicken cDNA clone showed high nucle-otide identity in the full-length coding region (.70%) and in the mature coding region (.80%). In addition, the deduced amino acid sequence of chicken bB subunit showed greater than 95 % identity compared to other species in the mature peptide region. Expression of the bB-subunit mRNA was detected by re-verse transcription-polymerase chain reaction in both gonadal and extragonadal tissues. Northern blot analysis detected ex-pression in the gonadal tissues only, specifically in the granulosa tissue from the F3-F5 follicles, small yellow follicles (SYF), large white follicles, and immature and mature rooster testes. A major transcript of approximately 4.1 kilobases (kb) and three minor transcripts of approximately 8.4 kb, 6.5 kb, and 1.7 kb were detected in the SYF granulosa samples. To examine the expres-sion pattern of the bB subunit around the stage of follicle selec-tion, the SYF granulosa was subdivided into two groups: 6–8 mm and 9–12 mm. Quantification of RNA expression (n 5 3) showed that expression of the bB subunit was maximal in the 6– 8 mm SYF. Activin B, as well as other intraovarian signals, may regulate early follicle selection and/or development in the chick-en