Generation and validation of animals allowing Pax4 ectopic expression in somatostatin-expressing cells. (A and B) Control Sst-Cre::ROSA26-β-gal double-transgenic mice were obtained by crossing Sst-Cre animals with the ROSA26-β-gal line (in which the Rosa26 promoter is upstream of a neomycin resistance-STOP cassette flanked by LoxP sites and followed by the β-galactosidase reporter; A). Sst-Cre mice were also crossed with Pax4-OE animals (in which the CAG promoter is upstream of the GFP-STOP flanked by LoxP sites and followed by the Pax4 and the β-galactosidase cDNA sequences; B). In the resulting Sst-Cre::Pax4-OE bitransgenic mouse line, somatostatin expression drives the expression of the Cre recombinase and allows the excision of the region between the two LoxP sites thereby promoting the expression of Pax4 and β-galactosidase (B). (C and D) β-Galactosidase and somatostatin immunodetection in Sst-Cre::ROSA26-β-gal double-transgenic mice (n = 4) confirmed Cre activity specifically in somatostatin-expressing cells. (E–G) In Sst-Cre::Pax4-OE islets (n = 4), Pax4 was detected in 66 ± 3.09% of the somatostatin-expressing cells (E and F) and was not found in glucagon⁺ cells (G). (H) Glycemia of nonfasted control and transgenic mice of different ages (1–2 mo, n = 5; 2–3 mo, n = 16; 3–5 mo, n = 10; 5–6 mo, n = 6; >7 mo, n = 5). The area under the curve (AUC) was measured and demonstrated no statistical differences between both groups (H). For Cre recombinase efficiency, the p-value was calculated using a one-sample t test. All values are depicted as mean ± SEM. Statistics for AUC were determined using the Mann–Whitney test. ****, P < 0.0001; ns, P > 0.05. Bars: 50 µm; (insets) 20 µm. β-gal, β-galactosidase; GCG, glucagon; SST, somatostatin.