Suv39h DKO stem cells show loss of heterochromatin structure and increased DNA damage. (A) Representative immunofluorescence staining of heterochromatin protein 1-α (HP1α) and colocalization with DAPI bright spots in fluorescence-activated cell sorted LSK cells of different genotypes. Images were captured on a Zeiss 880 LSM Laser Scanning Microscope with Airyscan using a 63× Oil Immersion Objective with Numerical Aperture of 1.4. (B) Quantification of colocalization index of thresholded HP1α staining with DAPI bright spots. Data are shown as individual data points together with mean and SEM. Statistical analysis by 1-way ANOVA with Holm-Sidak post hoc test. n = 42, 68, 30, 37, respectively, pooled from at least 3 mice of each genotype. (C) Phospho-γH2AX staining of bone marrow cells from Suv39h1-deficient (h1KO), Suv39h1- and h2-deficient (DKO), and control chimeras. Median fluorescence intensity (MFI) is shown normalized to control levels. Individual data points are shown together with mean and SEM. Data were statistically analyzed by 1-sample Student t test (2-tailed) compared with a theoretical mean of 1.0. FITC, fluorescein isothiocyanate.