Isolation and characterization of the follicle-stimulating hormone beta subunit gene and 5' flanking region of the Chinook salmon.

In this study we have isolated the follicle-stimulating hormone beta subunit gene from the Chinook salmon (csFSHbeta). This gene encodes for a protein that is highly similar to those isolated from other salmonids and shares all of the structural constraints seen in mammalian gonadotropins, including twelve conserved cysteines and a putative N-linked glycosylation site. The organization of the gene follows the conserved pattern regarding the numbers and positions of the introns, although the csFSHbeta gene contains a particularly large 6.2-kb first intron due to the inclusion of several transposon-like elements. Isolation of 1.2 kb of the 5' flanking region of the csFSHbeta gene and subsequent analysis in silico have revealed a number of putative elements which appear highly conserved in teleost FSHbeta gene promoters and are thus likely involved in basal and hormone-induced transcriptional regulation. The functionality of this 1.2-kb fragment in driving expression of a reporter gene and its response to GnRH was shown in gonadotropes, while the overexpression of AP-1 factors, Sf-1, estrogen receptor or Smad1 revealed that the promoter is responsive to these transcription factors. Our current study has opened the way for future analysis to verify the role of these factors in mediating hormonally induced transcription of this gene.