Conditional Mutagenesis of Mll2. (A) Scheme of the Mll2 protein, which contains several domains and motifs including AT hooks; SNLs (speckled nuclear localization sequences); the CxxC DNA binding region; three PHD fingers and an extended PHD finger (ePHD); a sequence similar to a Bromo domain; the FYR-N and -C domains (which dimerize); a transactivation domain (TD); a cleavage site (CS) for Taspase; and the SET domain, which is the H3K4 methyltransferase domain. (B) Scheme of the strategy for conditional mutagenesis. The CreERT2 protein was ubiquitously expressed from the Rosa26 locus but repressed by the Hsp90 complex. Tamoxifen binding releases CreERT2 from Hsp90 to permit Cre recombination of the loxP sites surrounding exon 2 of Mll2, which causes a frame-shift mutation. (C) A Southern blot to determine recombination efficiency in Mll2F/F; Rosa26-CreERT2/+ ES cells at various timepoints (0 to 96 hours) after addition of 4-hydroxy tamoxifen. (D) The same time course as shown in (C) was evaluated for Mll2 protein levels by western blotting. Wild type (wt) and Mll2-/- ES cells served as controls. (E) Summary of microarray expression profiling from Mll2-/- (constitutive) cells compared with wt or FLP rescued cells and tamoxifen-treated (conditional) compared with untreated mll2F/F; Rosa26-CreERT2/+ cells. At the left, the summary shows the number of genes whose mRNA expression level increased or decreased at least 1.7-fold in either the constitutive or conditional experiment. At the right, the overlap between the down-regulated genes in the two experiments is shown, along with the number of CpG island promoters in the three categories.