Figure 3. Recombination in ‘off-target’ tissues of neural-specific cre driver lines.

(a,b′) Select adult (P56) tissue sections indicating off target recombination in several neural-specific cre lines after crossing to the R26R-lacZ reporter line. (a,h,o,v) Cre-mediated β-gal expression in Thy1-cre (a), Grik4-cre (h), GFAP-cre (o) and Cyp39a1-cre (v) target tissues (brain). (b–g) Additional cre activity in Thy1-cre mice is present in the myocardium and vascular endothelium (b), lung tissue (arrowheads) (c), renal tubules (d), skeletal muscle, hair follicles, skin (arrowheads) (e), seminiferous tubules (f) and smooth muscle and urothelial cells of the bladder (arrowheads) (g). (i–n) Off-target cre activity in Grik4-cre mice is observed in the myocardium (i), lung tissue (j), renal tubules (k), skeletal muscle (l), smooth muscle cells of the intestine (m) and myometrium (n). (p–u) Observed off-target cre recombinase expression in Gfap-cre mice occurs in the endocardium (p), pulmonary vascular endothelium (q), endothelial cells of the liver portal system (r), ductus epididymis (s), islets of Langerhan’s and pancreatic duct endothelium (arrowheads) (t), as well as endometrial and glandular endometrial cells of the uterus (arrowheads) (u). (w–b′) Unreported cre recombination is present in several tissues of the Cyp39a1-cre mouse including the myocardium, aortic endothelial cells (w), pulmonary vascular endothelium and bronchiolar epithelial cells (arrowheads) (x), hepatocytes (y), skeletal muscle, hair follicles, skin (arrowheads) (z), acinar cells (a′) and uterine smooth muscle cells and endometrium (arrowheads) (b′).