Histochemical detection of β-glucosidase activity in mouse tissues. (a, b) Cryostat sections of snap frozen small intestine from non-transgenic mice stained with BCI-glu. (a) Endogenous activity in the villus brush-border. (b) No activity following incubation at 65°C for 20 min. (c-i) BCI-glu staining of tissues from R26SYNbglAR (left of panel) and PGKcrem/R26SYNbglAR (right of panel) mice: (c) heart and thymus, (d) spleen and pancreas, (e) kidney, (f) skeletal muscle, (g) liver, (h) glandular stomach and (i) brain. (j, k) Small intestinal wholemounts heat treated at 65°C and stained with BCI-glu from: (j) untreated Ahcre/R26SYNbglAR; (k) β-napthoflavone treated Ahcre/R26SYNbglAR mice (4 weeks post induction), showing detectable enzyme activity only in (k). (l-o) Wholemount of colon from an Ahcre/R26SYNbglAR mouse prepared 16 weeks after β-napthoflavone treatment and stained with Mag-glu (p, proximal; d, distal). (l) Extensive recombination occurs throughout as indicated by magenta staining but becomes increasingly variegated towards the distal end. (m-o) Shows enlargements of areas indicated by arrows. Punctate magenta staining corresponds to individual colonic crypts. Bars: A, B 200 μm, C-O 1 cm.