An Enhancer Within Abcb11 Regulates G6pc2 in C57BL/6 Mouse Pancreatic Islets

Abstract

<p><i>G6PC2</i> is predominantly expressed in pancreatic islet beta cells where it encodes a glucose-6-phosphatase catalytic subunit that modulates the sensitivity of insulin secretion to glucose by opposing the action of glucokinase, thereby regulating fasting blood glucose (FBG). Prior studies have shown that the <i>G6pc2</i> promoter alone is unable to confer sustained islet-specific gene expression in mice, suggesting the existence of distal enhancers that regulate <i>G6pc2</i> expression. Using information from both mice and humans, and knowledge that single nucleotide polymorphisms (SNPs) both within and near <i>G6PC2</i> are associated with variations in FBG in humans, we identified several putative enhancers 3' of <i>G6pc2</i>. One region, herein referred to as enhancer I, resides in the 25<sup>th</sup> intron of <i>Abcb11 </i>and<i> </i>binds multiple islet-enriched transcription factors<i>. </i>CRISPR-mediated deletion of enhancer I in C57BL/6 mice had selective effects on the expression of genes near the <i>G6pc2</i> locus: in isolated islets <i>G6pc2</i> and <i>Spc25 </i>expression were reduced ~50%, and <i>Gm13613 </i>expression was abolished, whereas<i> Cers6 </i>and<i> Nostrin </i>expression were unaffected. This partial reduction in <i>G6pc2 </i>expression enhanced islet insulin secretion at basal glucose concentrations but did not affect FBG or glucose tolerance <i>in vivo</i>, consistent with the absence of a phenotype in <i>G6pc2 </i>heterozygous C57BL/6 mice.</p>