Hdac1 and Hdac2 collectively show obligate haploinsufficiency in tumor suppression. (A) Quantification of thymocytes in 1-week-old WT and LckCre;Hdac1^Δ/Δ;Hdac2^Δ/Δ (DKO) mice (n = 3 mice per genotype). (B) Apoptosis in thymi of 1-week-old WT and DKO mice, as determined by annexinV and PI staining. Mean percentages and standard deviations of apoptotic (annexinV⁺PI^-) cells are presented on top (n = 3 mice per genotype). (C) Representative CD4/CD8 (top panel) and CD25/CD44 (bottom) flow cytometry dot plots of thymocytes from 1-week-old WT and DKO mice. Scheme on the right indicates DN stages of thymocyte development. (D) Quantification of thymic subsets in 1-week-old WT and DKO mice. DN = CD4^-CD8^-; DP = CD4⁺CD8⁺; CD4 SP = CD4⁺CD8^-; CD8 SP = CD4^-CD8⁺; DN1 = CD25^-CD44⁺; DN2 = CD25⁺CD44⁺; DN3 = CD25⁺CD44^-; DN4 = CD25^-CD44^-. WT, wild type.