Inhibition of TGF-β1 signaling increases Ptl numbers and reduces WBC counts and frequency of poikilocytes but does not affect Hct levels in blood of Gata1^low mice. Hct (A), Ptl numbers (B), and WBC counts (C) of Gata1^low mice during treatment with SB431542 (red, 12 mice) or vehicle (black, 8 mice), as indicated. The vertical lines indicate the time of the treatment (see also supplemental Figure 1). The results are compared with those of untreated age- and sex-matched wild-type (gray box) and Gata1^low (pink box) controls (10 mice each). Results are presented as mean (±SD) of independent measurements and analyzed with the mixed effects regression models using Restricted Maximum Likelihood Method, as summarized in the corresponding tables, on the right. (D) May-Grunwald staining of blood smears from representative untreated wild-type and Gata1^low mice and Gata1^low mice from vehicle- or SB431542-treated Gata1^low mice. Representative poikilocytes are indicated by arrows. Original magnification ×40.