Fig. 2.

X-gal staining of Col2CreER^T2;Rosa^LacZ mice. (A) Two-week-old Col2CreER^T2;Rosa^LacZ double transgenic mice were injected with tamoxifen (TM) (0.1 mg/g body weight, intraperitonal injection daily for 5 days). Mice were sacrificed at ages of 1, 2, 3 and 4 months (a–d) and disc samples (L3/L4) were fixed, decalcified and processed for frozen section preparation. X-gal staining was followed by counterstaining with nuclear fast red. Col2CreER^T2 targeted cells are lacZ-positive and stained blue. Recombination efficiency was evaluated by counting LacZ-positive cells divided by the total cell number in the growth plate, cartilage endplate, inner and outer annulus fibrosus (AF), and nucleus pulposus (NP) regions. High Cre-recombination efficiency in growth plate and inner AF cells is observed in Col2CreER^T2 transgenic mice 1, 2, 3 and 4 months after TM induction. Relatively lower Cre-recombination efficiency is found in the cartilage endplate and outer AF cells. No lacZ-positive cells are found in the NP region. (B) Evaluation of Cre recombination efficiency. TM was administered to 2-week-old Col2CreER^T2;Rosa^LacZ mice and mice were sacrificed 1 month after TM induction. X-gal staining was performed and sections (L3/L4) were then counterstained with nuclear fast red. Total and X-gal-positive cell numbers were counted in the growth plate, cartilage endplate, inner and outer annulus fibrosus and nucleus pulposus regions. (C) The table demonstrated Col2CreER^T2-mediated Cre-recombination efficiency in different regions of disc cells. This figure was adapted from Jin et al. (2011).