Inhibition of TGF-β1 signaling reduces splenomegaly in Gata1^low mice. (A) Morphological appearance (original magnification ×1.5), (B) weight, and (C) total cell number of a representative spleen from vehicle- and SB431542-treated Gata1^low mice, as indicated. (D) Frequency by flow cytometry for CD117/CD34 expression and total number of progenitor cells, (E) frequency by flow cytometry for Ter119/CD71 expression and total number of erythroid cells, and (F) frequency by flow cytometry for CD61/CD41 expression and total number of MKs in the spleen from vehicle- and SB431542-treated Gata1^low mice are also presented. Results are compared with those observed in untreated Gata1^low and wild-type animals (pink and gray horizontal bars). Total numbers of progenitor cells, erythroid cells, and MKs are calculated by multiplying the frequency of the different populations obtained by FACS (Table 6) per the total number of cells in the organs of the animals analyzed in these experiments and are presented as mean (±SD) of 5-6 independent determinations per experimental point. Values statistically different (P < .05) between untreated wild-type and Gata1^low mice and vehicle- and SB431542-treated Gata1^low mice are indicated by ^& and *, respectively.