Fig. 3.

Examples of spontaneous Cre activity in some osteocytes with age and induction of more osteocyte-specific Cre activity with tamoxifen. a Brightfield, DAPI and TdTomato images of the femur in 2 day old Sost ER^T2 Cre/tdTomato mice without tamoxifen treatment at 4x and 20x magnifications show no spontaneous Cre activity. b Percentage of positive osteocytes in tail vertebrae in single animals at 2 mo before injection of tamoxifen (Baseline) and at 3 months of age after tamoxifen injection (Tam + 1 mol·L⁻¹) and at 5 mo before injection of tamoxifen and 6 mo of age after tamoxifen injection is shown. The 3–5th caudal tail vertebra in females and males in Cre^– control mice, Cre⁺ injected with vehicle, Cre⁺ injected with tamoxifen are shown. Some spontaneous induction of Cre activity occurs in the absence of tamoxifen. Cre-mediated recombination was higher in males than in females. One 5 mo old male animal showed 86% baseline or spontaneous Cre activity. c and d Images of the tdTomato fluorescent reporter to indicate Cre-mediated recombination in the tail vertebrae of male and female Sost ER^T2 Cre/tdTomato mice with and without tamoxifen treatment at baseline and 1 month after tamoxifen injection (c. 2 mo and d. 5 mo). Cre^– controls with vehicle injection are also shown. These images are from the same animals as shown in 3b. The scalebars represent 100X