Expression and Regulation of the β-Subunit of Ovine Follicle-Stimulating Hormone Relies Heavily on a Promoter Sequence Likely to Bind Smad-Associated Proteins

FSH is essential for normal gonadal function in mammals. Expression of its β-subunit (FSHB) controls overall production/secretion of FSH and is induced by activin. Studies with ovine FSHB promoter/reporter constructs in LβT2 gonadotropes show that induction by activin requires a putative Smad binding element in the ovine FSHB promoter (-162AGAC-159). Similar studies reported here show that another site, juxtaposed to the Smad binding element, was also required for 81% activin induction in LβT2 cells. This site was similar to several that bind proteins known to partner with Smads. When this site (-171ACTgcgtTT-163) was mutated by changing the nucleotides shown in lowercase letters, the resulting ovine-derived construct (mut-oFSHBLuc) was expressed poorly as a transgene in primary mouse gonadotropes (<0.001 times compared with ovine wild-type transgenes). This decrease in expression demonstrated the importance of this site for activin induction and, perhaps, basal expression, although studies with LβT2 cells did not suggest this latter possibility. Expression of mut-oFSHBLuc in male mouse gonadotropes in vivo was at least 644 times greater than expression in all but one nongonadotrope tissue tested, indicating that mut-oFSHBLuc retained significant gonadotrope-specific expression. An increase in FSHB expression occurs during estrus in mice and is faithfully reproduced with wild-type ovine FSHBLuc transgenes, but not with mut-oFSHBLuc, indicating that the mutated site is needed for this secondary FSH surge. These data suggest that activin gathers Smads and Smad-associated proteins at the −171/−159 promoter region to regulate expression of the ovine FSHB and overall FSH production.