[Expression of inhibin alpha and inhibin/activin beta A subunits in the developing follicles of the duck].

The very sensitive quantitative competitive reverse transcription-polymerase chain reaction (RT-PCR) was used to investigate the expression of mRNA for the inhibin alpha and inhibin/activin beta A subunit in the developing ovarian follicles of the duck. The results indicated all follicles showed the expression of mRNA for the inhibin alpha and inhibin/activin beta A. The inhibin alpha subunit mRNA is expressed more abundantly than the beta A subunit in the large preovulatory follicles. Competitive RT-PCR revealed that the expression of inhibin alpha subunit is the highest in small yellow follicles (SYF), the mean relative content for the F1, F2, F3, F4/5 and LWF (large white follicle) was 0.26 +/- 0.05, 0.28 +/- 0.07, 0.57 +/- 0.12, 0.98 +/- 0.09 and 0.026 +/- 0.006, respectively, compared to a mean relative content of 1.00 for the SYF. The highest level of inhibin/activin beta A mRNA was found in the F1 follicle, the mean relative content for the F2, F3, F4/5, SYF and LWF was 0.218 +/- 0.09, 0.111 +/- 0.03, 0.058 +/- 0.011, 0.053 +/- 0.013 and 0.005 +/- 0.002, respectively, compared to a mean relative content of 1.00 for the F1 follicle. Our data suggest that the expression of the alpha subunit is reduced with follicular development whereas beta A subunit expression is dramatically enhanced, which indicates the expression of inhibin alpha and inhibin/activin beta A subunit is differentially regulated during follicular development. In addition, the highest level of beta A mRNA in F1 follicle indicates the production of dimeric inhibin and/or activin primarily occurred in the largest F1 follicle.