RhoA deletion disrupts megakaryocyte development.

<p>(A) The differences in spleen weights were not statistically significant. (B) When <i>adult</i> RhoA-null platelets were infused into mαIIb^−/−/hαIIb^+/+ mice, the time course of platelet survival was similar to that of their controls. Differences were not statistically significant. Shown is the mean ±SE (N = 3). Values were normalized to platelet levels at the initial draw for each experimental group (30 minutes after infusion). (C) Flow cytometry revealed that the megakaryocyte population, as a percentage of the total bone marrow cells, was diminished in the RhoA^fl/fl PF4CRE⁺mice. Megakaryocytes were discriminated by size and by the use of a FITC-labeled anti-CD41 antibody. Mean ± SE is shown. N = 3. (D) On the top is a representative image of a normal megakaryocyte, and on the bottom is a megakaryocyte (arrow) undergoing apoptosis that is exhibiting dark, pyknotic nuclei and scant cytoplasm. In the bone marrow and in the spleen of RhoA^fl/fl PF4CRE⁺ mice, megakaryocytes are more likely to exhibit this phenotype. Magnification is 40×. (E) The RhoA-null megakaryocyte population has a higher ploidy than normal. Ploidy was calculated by DNA staining with propidium iodide, and we measured staining intensity with flow cytometry. Mean ± SE is shown; * indicates P<0.05. N = 3. (F) Megakaryocyte size (forward scatter) was measured as a function of ploidy. The results show that RhoA-null megakaryocytes were larger than the control cells at all ploidy. Mean ± SE is shown; * indicates P<0.05; ** indicates P<0.01. N = 4.