Inducible Cre Recombination in Transgenic Mice

Homozygous creER^T2 mouse lines were maintained on the Rosa26-YFP reporter background⁴⁷. Cre recombination was induced by administering tamoxifen (Sigma, 40 mg ml⁻¹), dissolved in corn oil by sonication for 45 min at 30 °C. Adult mice were given 300 mg per kg of body weight by oral gavage on each of 4 consecutive days starting at P45 or P180. In the corpus callosum of Pdgfra-creER^T2/Rosa-YFP mice, 45 ± 1% of PDGFRA⁺ OLPs were labeled for YFP; in the medial cortex, 49 ± 2% were labeled (means ± s.d., combining data from mice induced at P45 and analyzed 8, 14, 28 or 90 d post-tamoxifen; Fig. 3d). In Fgfr3-icreER^T2/Rosa26-YFP mice, practically all of the cells in the forebrain SVZ (including GFAP⁺ type-B cells) and a high proportion of Fgfr3-expressing astrocytes in the parenchyma labeled for YFP (Supplementary Fig. 3).