Inhibition of TGF-β1 signaling normalizes the number and expression profile of progenitor cells, erythroid cells, and MKs in BM of Gata1^low mice. (A) Frequency by flow cytometry for CD34/CD117 expression, (B), total numbers, and (C) expression profiling of Common erythroid/MK and common erythroid/MK and common myeloid/granulocyte/monocyte progenitors from BM of vehicle- and SB431542-treated Gata1^low mice. Results are compared with those observed with untreated Gata1^low and wild-type littermates (pink and gray horizontal bars). B (right) presents the total number of progenitor cells calculated on the basis of CFC evaluations. (D) Frequency by flow cytometry for Ter119/CD71 expression, (E) total numbers, and (F) expression profiling of erythroid cells from BM of vehicle- and SB431542-treated Gata1^low mice. (G) Frequency by flow cytometry for CD61/CD41 expression, (H) total cell number, (I) representative morphology by EM of MKs from BM of vehicle- and SB431542-treated Gata1^low mice, and (J) expression profiling. I, Magnification ×4400; Neu indicates a neutrophil. Total cell numbers were calculated by multiplying the mean frequencies presented in Table 6 per the total number of BM cells in the 3 animals analyzed in this experiment. Quantitative results are presented as mean (±SD) of at least 3 independent determinations with 3 mice per experimental point and are compared with those observed with the corresponding populations purified from untreated Gata1^low and wild-type animals (pink and gray horizontal bars). Values statistically different (P < .01) between untreated Gata1^low and wild-type animals and between vehicle- and SB431542-treated Gata1^low mice are indicated by ^& and *, respectively.