Disrupting the menin-MLL1 interaction affects shared target genes in B cells but not B-cell differentiation. (A) Experimental design for expressing the disrupting peptide in wild-type BM cells and assays to measure its activity. (B-C) The selective effect of the disrupting peptide on the expression levels of several shared target genes in cultured BM B cells. B220-enriched BM cells were infected with peptide-expressing or empty (MIG) retrovirus and GFP⁺ cells were sorted 6 to 10 days later for qRT-PCR assays. (D) The effect of peptide expression on B-cell growth in vitro. BM was depleted of lineage-positive cells and the resulting lineage-depleted population was cultured overnight and then infected with peptide-expressing or empty retrovirus. The hatched bar shows the B-cell growth using BM from Rag1-cre;Men1^f/f infected with empty retrovirus. The B-cell percentages were determined at day 8 by flow cytometry. Error bars represent 95% confidence intervals from 3 replicate infections. (E-F) The effect of the peptides on gene expression in B cells expanded in vitro. GFP⁺ cells as described in panel D were used for qRT-PCR assays on day 6. Relative expression levels of the genes indicated below each set of bars reflect data normalized to ribosomal RNA expression. All experiments were reproduced 3 times. Statistical significance was determined using the unpaired Student t test; error bars represent 95% confidence intervals; ***P ≤ .001; **P ≤ .01.