Expression pattern of messenger ribonucleic acid for the activin type II receptors and the inhibin/activin subunits during follicular development in broiler breeder hens

The expression of mRNA for the activin type II receptors (ActRII and ActRIIB), follistatin, and the inhibin/activin subunits was investigated in the follicles of broiler breeder hens. Total RNA was isolated from individual granulosa and theca layers of the F(1), through F(5) follicles, a pool of the F(6) and F(7) follicles, the small yellow follicles, and from the combined granulosa and theca layers of the large white follicles from six birds. Northern blot analysis was performed, and two ActRII mRNA transcripts of 6.5 and 3.7 kb were detected in granulosa and theca samples. Both ActRII transcripts were equally expressed in the granulosa samples, but in the theca samples expression of the 3.7-kb transcript was greater than the 6.5-kb transcript. ActRIIB was not detected by Northern analysis in any of the samples. Expression of the mRNA for the activin/inhibin binding protein, follistatin, was detected in theca and granulosa samples with the greatest expression found in small yellow follicle samples for both cell layers. Expression of the inhibin asubunit was detected in the granulosa layer of all the follicles, but expression was greatest in the F(6) and F(7) follicles. Granulosa from the large hierarchical follicles expressed the most inhibin/activin beta(A)-subunit, whereas expression of the inhibin/activin beta(B)-subunit was greatest in the granulosa of small yellow and F(6) and F(7) follicles. This report is the first, to our knowledge, on detection of activin type II receptor mRNA in the hen ovary and characterization of the expression pattern of the inhibin family in both the theca and granulosa layers throughout follicular development. The presence of activin receptor and follistatin mRNA in the theca and granulosa layers of the small developing follicles suggests that locally produced activin may be highly regulated and have a vital role in early follicular development.