Characterization of mice expressing Ins1 gene promoter driven CreERT recombinase for conditional gene deletion in pancreatic β-cells.

Gene manipulation using Cre-loxP recombination has proven to be an important approach for studying the impact of gene expression on pancreatic β-cell biology. We report the generation of a transgenic mouse line that enables a highly specific system for conditional gene manipulation within β-cells and achieve tissue specific and temporally regulated deletion of the Ctnnb1 (β-catenin) gene in pancreatic β-cells. cDNA encoding Cre recombinase fused to modified estrogen receptor (CreERT) under control of mouse insulin 1 gene promoter (Ins1) was used to construct the mouse line Tg(Ins1-Cre/ERT)1Lphi, also termed MIP1-CreERT. In a cross of MIP1-CreERT with a ROSA26/LacZ reporter strain, tamoxifen [Tmx] - dependent β-galactosidase expression occurred within pancreatic β-cells but not in other organ systems. Intraperitoneal glucose tolerance tests and glucose-stimulated changes in β-cell cytoplasmic calcium concentration were not adversely affected in adult MIP1-CreERT. A mouse line with floxed Ctnnb1 gene (Ctnnb1f/f) was crossed with the MIP1-CreERT line to generate a mouse model for inducible β-cell specific deletion of β-catenin gene (Ctnnb1f/f:MIP1-CreERT). Ctnnb1f/f:MIP1-CreERT mice and Ctnnb1f/f littermate controls, were injected with Tmx as adults to knock down β-catenin production in the majority of pancreatic β-cells. These mice showed normal glucose tolerance, islet cyto-architecture and insulin secretion. A novel protein fraction of 50Kd, immunoreactive with anti-β-catenin was observed in islet extracts from Ctnnb1f/f:MIP1-CreERT[Tmx] mice but not MIP1-CreERT-negative Ctnnb1f/f[Tmx] controls, indicating possible presence of a cryptic protein product of recombined Ctnnb1 gene. The MIP1-CreERT mouse line is a powerful tool for conditional manipulation of gene expression in β-cells.