Characterization of sea bass FSHß 5' flanking region: transcriptional control by 17ß-estradiol.

ABSTRACT

The sea bass follicle-stimulating hormone 5' flanking region (sbFSHß 5' FR) was cloned and characterized in order to study the molecular mechanisms underlying transcriptional regulation of the sbFSHß gene. Analysis of the ~3.5 kb of this region revealed the presence of several putative cis-acting elements, including steroid hormone response elements, cAMP response elements, pituitary-specific transcription factor response elements, activator protein-1 response elements and TATA sequence. Deleted constructs containing ~3.5 kb of the sbFSHß 5' FR fused to a luciferase reporter gene were transiently transfected into human embryonic kidney (HEK 293) and mouse mature gonadotrope (LßT2) cell lines. The sbFSHß 5' FR was efficiently expressed under basal conditions in LßT2 but not in HEK 293, pointing to both positive and negative regulatory elements. In order to elucidate the estrogen-mediated sbFSHß transcriptional activity, in vitro treatments with 17ß-estradiol were carried out on primary cultures of pituitary cells and LßT2 cells transiently expressing luciferase under the control of sbFSHß 5' FR. Overall, these results demonstrate that 17ß-estradiol inhibits sbFSHß gene expression directly at the level of the pituitary. However, it was also shown that estrogen did not induce changes of the sbFSH promoter-directed luciferase activity, suggesting that sbFSHß 5'FR (~3.5 kb) activity is cell type dependent and its estrogen regulation could require cis-acting elements located upstream of the promoter region, which is characterized in this article.