Deletion of Men1 during lymphocyte differentiation results in a partial block in B-cell differentiation. (A) Pro-B (B220⁺/CD43⁺), small pre-B (B220⁺/CD43⁻/IgM⁻), immature B (B220⁺/CD43⁻/IgM⁺), and (B) splenic B cells (B220⁺) were quantified in the BM of Men1^f/f or Rag1-cre;Men1^f/f animals. (C) Representative fluorescence-activated cell sorter plot illustrating partial fraction C-to-C′ block. (D) Fraction C to fraction C′ ratio comparing Men1^f/f to Rag1-cre;Men1^f/f mice. Fraction C (B220⁺/CD43⁺/BP-1⁺/HSA^lo) to fraction C′ (B220⁺/CD43⁺/BP-1⁺/HSA^hi) ratios were determined using absolute numbers of the gated populations in the hind limbs of either genotype. (E) Relative expression of Hoxa9 and Meis1 in pro-B cells (B220⁺/CD43⁺) from Men1^f/f (black bars) or Rag1-cre;Men1^f/f animals (white bars). Relative expression levels were determined using ribosomal RNA as an internal control. Three- to 4-week-old animals were analyzed, n = 3-4 animals per genotype. Statistical significance was determined using the unpaired Student t test; error bars represent 95% confidence intervals; ***P ≤ .001; **P ≤ .01.