In vivo and in vitro megakaryopoiesis. (A) Sections of mouse spleen and femur bone marrow of control and FlnA^loxP PF4-Cre mice were stained with H&E to reveal megakaryocytes. Sections shown are representative of 5 mice for each genotype. (B-C) Spleen and bone marrow MKs were quantified per field of view. Data represent the mean ± SD of 5 or 6 fields (5 mice for each genotype). *P < .05. (D) Percentage of CD61⁺ MKs differentiated from fetal livers in control and FlnA-null cultures. Results are expressed as mean ± SD (n = 8). (E) Ploidy analysis of fetal liver-derived control and FlnA-null MKs. Results are representative of 6 independent experiments. (F) Percentage of MK ploidy. Data are mean ± SD (n = 6). *P < .05.