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Abstract
Glucose-dependent insulinotropic polypeptide (GIP), an important component of the
enteroinsular axis, is a potent stimulator of insulin secretion, functioning to maintain
nutrient efficiency. Although well-characterized in mammals, little is known regarding
GIP transcriptional regulation in Danio rerio (Dr). We previously demonstrated that
DrGIP is expressed in the intestine and the pancreas, and we therefore cloned the
Dr promoter to compare GIP transcriptional regulation in Dr and mammals. Although
no significant homology was indentified between the highly conserved mammalian promoter
and the DrGIP promoter, 1072-bp of the DrGIP promoter conferred tissue-specific expression
in mammalian cell lines. Deletional analysis of the DrGIP promoter identified two
regions that, when deleted, reduced transcription by 75% and 95%, respectively. Mutational
analysis of the upstream region suggested involvement of an Nkx binding site, although
we were unable to identify the factor binding to this site. The cis element in the
downstream region was found to be a GATA binding site. Lastly, overexpression and
shRNA experiments identified PAX4 as a potential repressor of DrGIP expression. These
findings provide evidence that despite the identification of species-specific transcriptional
regulators and differences in GIP expression patterns between D. rerio and mammals,
a moderate degree of regulatory conservation appears to exist.
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