EXPRESSION OF INHIBIN-ALPHA AND INHIBIN ACTIVIN-BETA(3) SUBUNITS IN THE GRANULOSA LAYER OF THE LARGE PREOVULATORY FOLLICLES OF THE HEN/

The expression of the mRNA for the inhibin/activin subunits (alpha and beta(A)) in the granulosa layer of the five largest preovulatory foll icles of the hen was investigated. Total RNA from the granulosa layer of the F-5 (the fifth largest) to F-1 (the largest) follicles was extr acted and analyzed by Northern blot analysis using homologous chicken inhibin alpha and beta(A) subunit cDNA probes. RNA loading was quantif ied by a cDNA probe of bovine 185 rRNA. Results showed that for the ch icken inhibin alpha subunit mRNA signals (n = 3), the mean relative in tensity for the F-1, F-2, F-3, and F-4 follicles was 0.50 +/- 0.10 (+/ - SEM,), 0.52 +/- 0.08, 0.59 +/- 0.06, and 0.81 +/- 0.04, respectively , compared to a mean relative intensity of 1.00 (p < 0.05) for the F-5 follicle. For the beta(A) subunit mRNA signals (n = 3), the mean rela tive intensity for the F-5, F-4, F-3, and F-2 follicles was 0.25 +/- 0 .06, 0.28 +/- 0.15, 0.40 +/- 0.17, and 0.48 +/- 0.10, respectively, co mpared to a mean relative intensity of 1.00 (p < 0.05) for the F-1 fol licle. The inhibin alpha subunit was also estimated to be more abundan tly expressed among follicles in the granulosa layer than was the beta (A) subunit. Our data indicate that the expression of inhibin alpha an d beta(A) subunits is differentially regulated in the hen granulosa la yer during follicular development. Expression of the alpha subunit is reduced with follicular development whereas inhibin beta(A) subunit ex pression is dramatically enhanced. In addition, the granulosa layer of the large preovulatory follicles may produce more inhibin alpha subun it than beta(A) subunit, and the F-1 follicle may be the primary sourc e of the beta(A) subunit for dimeric inhibin and/or activin in the hen .