A FUNCTIONAL-STUDY OF THE SALMON GNRH PROMOTER

The Pa and Pb promoters of the Atlantic salmon (Salmo salar) GnRH gene were fused together or individually to the Escherichia coli lacZ gene , and their transcriptional activities were measured in transient expr ession assays in zebrafish (Danio rerio). In 48-hour embryos, both pro moters were preferentially expressed in the brain, whereas a cytomegal ovirus (CMV) promoter-lacZ fusion gene displayed high levels of activi ty in nonbrain tissues. Pa and Pb exhibited different cell specificity in the forebrain. Pb was active in large neuron-like cells exclusive in the olfactory placode region, whereas Pa appeared active in nonneur on-like cells in the forebrain. In Atlantic salmon forebrain tissue, b oth Pa and Pb exhibited endogenous activity, as assessed by reverse tr anscriptase-polymerase chain reaction (RT-PCR) analysis. However, only the Pb transcript contained the prepro-GnRH exon II-IV sequences, sug gesting that Pa activity may not be related to GnRH production in this species.