Expression of Mkl1 during megakaryocyte differentiation. (A) Freshly isolated E12.5-E14.5 fetal liver cells were differentiated in the presence of TPO, IL-6, and IL-11. At day 4, different cell types (myelomonocytic cells vs megakaryocytes) were separated on a discontinuous BSA gradient. Analysis of cell ploidy validates the megakaryocyte fractionation. (B) Relative Mkl1 mRNA levels were assessed by quantitative RT-PCR on fetal liver subpopulations. The RNA from total fetal liver cells was used from day 0 to day 4 (left). At day 4, RNA from fractionated cells was used (right). The relative expression levels were normalized to 18S rRNA. (C) c-kit+CD41+ BM cells were sorted (day 1) and cultured with TPO for 4 more days. RNA at different time points was used to assess relative Mkl1 levels by quantitative RT-PCR. The Mkl1 expression was normalized to 18S rRNA or absolute cell number. Mean plus or minus SEM of duplicate experiments is represented.