The 5' untranslated region (UTR) of PA inhibin mRNA was compared in a variety of sheep tissues, using primer extension. Considerable variation in the length and number of 5' extended products were noted between tissues. Specific bands were noted in ovarian follicular RNA, which were also present in samples from corpora lutea, strorna, and placental cotyledon RNA. Other extended products were observed in RNA from corpora lutea, stroma, cotyledon, pituitary, bone marrow, frontal cortex, medial basal hypothalamus, adrenal, liver, and kidney, which were not present or weakly represented in follicular RNA. Additional tissue-specific bands were noted in testis and bone marrow RNA. No specific differences in the lengths of the 5' UTR of the PA inhibin mRNA were observed in sheep homozygous for the Booroola fecundity gene FecB, in any tissue studied. The coding region of ovine PA inhibin cDNA was sequenced and a genetic polymorphism confirmed within or close to the ovine PA inhibin gene.
W e conclude that the PA inhibin gene is expressed widely in the sheep. Furthermore there is variation in the length of the 5' UTR of PA inhibin mRNA between male and female gonads and other tissues, implying that expression of this gene is differentially controlled. However, the fecB mutation does not affect mRNA splicing events or the initiation site used in ovarian transcription. The mechanism by which the fecB mutation influences the amounts of PA inhibin mRNA, follicle-stimulating hormone (FSH) secretion and ovulation rate has still to be elucidated.