Regulatory regions in the promoter and third intron of the growth hormone gene in rainbow trout, Oncorhynchus mykiss Walbaum

The mechanisms involved in the transcriptional regulation of the rainbow tr out (Oncorhynchus mykiss) growth hormone (tGH) gene have been investigated. Transient transfection assays, using deletion mutants of the tGH promoter, demonstrated that the -226/+24 5'-flanking region, bearing three binding s ites for the pituitary-specific transcription factor GHF1/Pit1 and a cAMP-r esponse element, is necessary and sufficient to confer strong tissue-specif ic and cAMP-stimulated expression to a luciferase reporter gene. This regio n is also upregulated by the synthetic glucocorticoid dexamethasone (DEX), the,combined effects of cAMP, and DEX being synergistic. Footprinting and g el shift assays revealed that CHF1 binds to a recognition element in the th ird intron of the tGH gene, suggesting that GHF1 can affect the expression of this gene by interacting with response elements in the transcription uni t. These results may be exploited to design tGH gene constructs for the pro duction of autotransgenic fish, in which the expression of the isospecific transgene driven by a constitutive proximal promoter is specifically target ed to the pituitary and physiologically controlled. (C) 1999 Academic Press .