Ligand-induced mutagenesis of Mll2 in utero , via lactation and in adults. (A) Southern blot of tamoxifen-induced CreERT2 recombination in various tissues of a 2-month-old Mll2F/F; Rosa26-CreERT2/+ male two weeks after tamoxifen administration. The first lane shows tail DNA before tamoxifen administration with the 3.4 kb unrecombined band. All other lanes show DNAs after tamoxifen displaying the recombined 2.6 kb band. (B) Western blot of protein extracts from wild type and tamoxifen induced Mll2F/F; Rosa26-CreERT2/+ male testis and brain. The 300 kD protein, CBP, was used as a loading control. (C) Recombination efficiency in E10.5 embryos was detected by Southern blot. Pregnant mothers were untreated (-) or treated with one dose of 4 mg tamoxifen at E10 (12 h) or E8.5 (48 h). (D) The Mll2-/- phenotype was recapitulated in Mll2F/F; Rosa26-CreERT2/+ embryos after induction at E4.5 and E5.5 with doses of 1 mg tamoxifen. The embryos were harvested at E10.5. The inset shows a Mll2-/- embryo at E10.5 at the same scale. (E) Control Mll2F/+; Rosa26-CreERT2/+ embryos induced with tamoxifen at E4.5/E5.5 were normal at E10.5. (F, G) Mll2 is dispensable from E11.5. Mll2F/F; Rosa26-CreERT2/+ (F) and Mll2F/+; Rosa26-CreERT2/+ embryos (G) induced at E8.5 were normal at E12.5. (H) Southern blot of various tissues harvested from 14-day-old Mll2F/F; Rosa26-CreERT2/+ neonates, using the same strategy as in panel (A) and five daily doses of 4 mg tamoxifen to the lactating mothers, starting 4 days after delivery. (I) Body weight measurements after birth of Mll2F/F; Rosa26-CreERT2/+ or Mll2F/+; Rosa26-CreERT2/+ pups treated with tamoxifen or not as in panel (H).