Pax4-cre transgenic mice have the mouse paired box gene 4 (Pax4) promoter directing expression of an enhanced green fluorescent protein fused to a Tet-off cassette (EGFP/tTA). The transgene also contains a tetracycline-responsive element with a CMV minimal promoter (tetO-CMVmin) driving expression of a Cre-recombinase gene. In the absence of tetracycline/doxycycline, Cre recombinase expression is observed in Pax4-expressing cells (pancreatic progenitor cells). While designed to concomitantly allow tetracycline/doxycycline-dependant inhibition of Cre recombinase expression, the donating investigator confirms no such inhibition is observed. Also, no GFP expression is observed with or without tetracycline/doxycycline administration. Therefore, Pax4-cre transgenic mice function only for Cre recombinase expression in Pax4-expressing cells. When bred with mice containing a loxP-flanked sequence, Cre-mediated recombination will result in deletion of the floxed sequences in the Pax4-expressing cells of the offspring. While not useful as a Tet-Off tool, these mice may be useful as for studying pancreatic islet development and beta cell differentiation. For example, when bred to STOCK Gt(ROSA)26Sortm1(Notch1)Dam/J mice (Stock No. 008159), Notch activation inhibits the differentiation of pancreatic progenitor cells into _ and _ endocrine cells and shunts them instead toward a duct fate. The Jackson Laboratory 2024, used with permission.