Hdac1 and Hdac2 control pre–T-cell development in a dosage-dependent manner. (A) Tcrβ repertoire determined in 3-week-old WT and Hdac1^Δ/Δ;Hdac2^Δ/+ thymi by Southern blot analysis using a Jβ2 probe sequence (right panel). Hdac1^Δ/Δ;Hdac2^Δ/+ lymphoma DNA was used as a positive control, while ethidium bromide–stained gel served as a loading control (left panel). (B) Quantification of thymocytes from 1-week-old mice of the indicated genotypes (n = 3 per genotype). (C) Apoptosis in thymocytes of 1-week-old WT, LckCre;Hdac1^Δ/Δ and LckCre;Hdac1^Δ/Δ;Hdac2^Δ/+ mice, as determined by annexinV and PI staining. Mean percentages of apoptotic (annexinV⁺PI^-) cells are presented on top (n = 3 mice per genotype). (D) Representative dot plots of CD4/CD8 (top) and CD24/TCRβ (bottom) flow cytometric analyses of thymi from 1-week-old mice with indicated genotypes. (E) Quantification of thymic subsets of 1-week-old mice with indicated genotypes. DN = CD4^-CD8^-, DP = CD4⁺CD8⁺, CD4 SP = CD4⁺CD8^-, CD8 SP = CD4^-CD8⁺ (left); ISP = CD4^-CD8⁺CD24⁺Tcrβ^+/−, mature CD8 = CD4^-CD8⁺CD24^+/−Tcrβ⁺ (right). (F) Dot plots representing BrdU-7-AAD flow cytometric analysis of thymocytes from WT and LckCre;Hdac1^Δ/Δ;Hdac2^Δ/+ mice 1.5 hours after BrdU injection. Average and standard deviation of BrdU-positive thymocytes are indicated on top (n = 3 mice per group). WT, wild type.