EXPRESSION PATTERN OF MESSENGER-RIBONUCLEIC-ACID FOR FOLLISTATIN AND THE INHIBIN ACTIVIN SUBUNITS DURING FOLLICULAR AND TESTICULAR DEVELOPMENT IN GALLUS-DOMESTICUS/

The expression of mRNA for follistatin and the inhibin/activin subunit s was investigated in the follicles of laying hens and the testes of i mmature and mature roosters. Total RNA was isolated from immature and mature testes and from individual granulosa layers of the F-1 through F-5 follicles, from a pool of the F-6-F-8 follicles, from the small ye llow follicles, and from the combined granulosa and theca layers of th e targe white follicles. Northern blot analysis was performed, and a f ollistatin mRNA transcript of approximately 2.4 kilobases (kb) was det ected in immature testes and in the following follicles: F-5, the pool of F-6-F-8, and small yellow and large white follicles. The greatest expression of follistatin occurred in the small yellow follicles, and in this tissue two minor transcripts of approximately 1.7 and 3.7 kb w ere also detected. The inhibin alpha subunit was expressed in both tes tes samples and in all of the follicles except the large white follicl es. Expression of the alpha subunit was greatest in the F-5 follicle, and expression decreased with follicle maturity. As previously reporte d, the inhibin/activin beta(A) subunit was found in the greatest abund ance in the F-1 follicle, with lesser amounts detected in the other hi erarchical follicles and immature testes. In contrast to the beta(A) s ubunit, the inhibin/activin beta(B) subunit was not detected in the fo ur largest hierarchical follicles but was expressed in greatest abunda nce in the pool of F-6-F-8 and small yellow follicles. This represents the first report, to our knowledge, of the detection of follistatin m RNA in the hen ovary and rooster testes. The restriction of follistati n mRNA expression to the small follicles suggests that follistatin, by regulating activin and/or inhibin availability, may play a critical r ole in early follicular development.