ß cells; Cre recombinase is expressed in insulin-producing beta cells of pancreas. Ins1cre mice express Cre recombinase from the start codon of the Ins1 (Insulin I) gene, replacing the entire coding region. Insulin is a hormone produced by beta cells in the pancreas. It regulates the metabolism of carbohydrates and fats by promoting the absorption of glucose from the blood to skeletal muscles and fat tissue and by causing fat to be stored rather than used for energy. Homozygous mice are viable and fertile. When these mice are bred with mice containing loxP-flanked sequence, Cre-mediated recombination will result in deletion of the floxed sequences in the beta cells of the offspring. The donating investigator reports that no cre expression is seen in the central nervous system.