FUNCTIONAL-ANALYSIS OF ESTROGEN-RESPONSIVE ELEMENTS IN CHINOOK SALMON (ONCORHYNCHUS-TSCHAWYTSCHA) GONADOTROPIN II-BETA SUBUNIT GENE

The salmon gonadotropin II gene regulates ovulation and spawning. Analysis of the 5' flanking sequence of the hormone-specific beta-subunit of salmon gonadotropin II (sGTHII beta) gene reveals the presence of several presumptive estrogen-responsive elements (ERE). The participation of ERE in the control of sGTHII beta gene transcription was examined by the transient expression of sGTHII beta gene promoter-chloramphenicol acetyltransferase chimeric DNA constructs in HeLa cells, with the cotransfection of a rainbow trout estrogen receptor expression vector. Three ERE have been identified: the proximal ERE [pERE, at -267 base pair (bp) from the transcription start site], the distal ERE (dERE, at -2698 bp, three GGTCA motifs each separated by exactly 31 bp), and the half-ERE (1/2ERE, at -157 bp as a GGTCA motif), respectively. The pERE ((T) under bar GTCAATCTGACC) represents a novel but less effective variation of the consensus ERE (cERE). The dERE is a unique estrogen-induced enhancer. It requires the participation of the pERE to be functional and the enhancer activity of pERE and dERE is promoter specific. The contribution of 1/2ERE is minor and is not cell-type specific. The activation of the ERE in the sGTHII beta gene and the synergistic cooperation between the dERE and pERE by estradiol-17 beta is dose dependent. DNA sequences in the vicinity of the ERE decreases their hormone responsiveness and the synergism between dERE and pERE. These negative regions may contribute to the quiescent endocrine state of the sGTHII beta gene during the regressive phase of the reproductive cycle in teleost.