The bicistronic Ins1-2A-Cre knock-in allele was created using homologous recombination (aided by targeted CRISPR/cas9 endonuclease activity) to insert a viral 2A oligopeptide sequence (T2A; mediates ribosomal skipping) and a Cre recombinase gene (cre) just upstream of the endogenous STOP codon of Ins1. An annealed Ins1-CRISPR-F and Ins1-CRISPR-R were inserted into the entry site of plasmid carrying both gRNA and Cas9 expression units. DNA vectors were microinjected into the pronuclei of C57BL/6J fertilized zygotes. Embryos were transferred to pseudopregnant females.