Dysfunctional myeloid and erythroid cell development in the absence of Dnmt3a. (A) Increased frequency of GMPs but decreased frequency of MEPs in the bone marrow of Dnmt3a-KO MDS mice (n = 11) compared with control mice (n = 13). (B) Quantification of Ki67⁺ cells within bone marrow populations from Dnmt3a-KO MDS (n = 6-7) and control (n = 7) mice showed increased proliferation of Dnmt3a-KO myeloid progenitors (MPs). (C) Quantification of Annexin V⁺ cells within bone marrow populations from Dnmt3a-KO MDS (n = 8-10) and control (n = 9) mice showed increased apoptosis in Dnmt3a-KO mature myeloid cells (Gr-1⁺ Mac-1⁺) but not progenitors. (D) FACS analysis showing accumulation of immature erythroid progenitors (stage I and stage II) in the spleen of Dnmt3a-KO MDS mice. (E) Quantification of erythroid progenitors in the spleens of Dnmt3a-KO MDS (n = 12) and control (n = 10) mice showed arrest of Dnmt3a-KO progenitors at stage I (proerythroblast) and stage II (basophilic erythroblast) of erythroid development, leading to a subsequent decrease in the more mature stage IV (orthochromatophilic erythroblast) cells. (F) Quantification of erythroid progenitors in the bone marrow of Dnmt3a-KO MDS (n = 12) and control (n = 10) mice. (G) Apoptosis analysis of erythroid progenitors in the spleens of Dnmt3a-KO MDS (n = 6) and control (n = 6) revealed no differences in percentages of Annexin V⁺ cells, suggesting the accumulation of Dnmt3a-KO early progenitors arose from a block in developmental progression. (H) Apoptosis analysis of erythroid progenitors in the bone marrow of Dnmt3a-KO MDS (n = 6) and control (n = 6) mice. * P < .05, ** P < .01, *** P < .001.