Loss of both Suv39h1 and Suv39h2 enzymes results in poor HSC potential and a reduced frequency of long term HSCs. (A) Schematic of primary and secondary hematopoietic reconstitution of different genotype donor (CD45.2⁺) cells into lethally irradiated (2× 550 Gy) recipient hosts (CD45.1⁺). Suv39h1-deficient, (h1KO), Suv39h2-deficient (h2KO) are matched with littermate WT cells, and double Suv39h-deficient (DKO) are matched with littermate control (Con) cells (Suv39h2^het). (B-C) Frequency of donor-derived (CD45.2⁺) total white blood cells (WBC) for each transplanted mouse through 8 weeks in primary (B) and secondary (C) recipients. Individual data points together with mean and standard error of the mean (SEM) are shown. Data were statistically analyzed by 1-way analysis of variance (ANOVA) with Sidak multiple comparisons test comparing each genotype with relevant control. (D) Frequency and number of LSK cells and frequency of long-term HSC enriched (CD150⁺) cells in bone marrow from Control, h1KO, and DKO chimeras. Individual data points together with mean and SEM are shown. Data were statistically analyzed by 1-way ANOVA with Dunnett post hoc test. (E) Schematic of competitive hematopoietic reconstitution of different genotype donor cells into lethally irradiated (2× 550 Gy) F1 recipient hosts. (F) Frequency of CD45.2⁺ white blood cells from each competitive chimera depicted in panel D. Data shown as individual data points together with mean and SEM. Data were normalized to the mean of the control group, which was set at 50%, and were statistically analyzed by 1-way ANOVA with Sidak multiple comparisons test comparing each genotype with Control. ns, not significant.