Induced deletion of Smad1 and Smad5, but not Smad1 alone, results in death because of pathology in the colon. (A) Weight change after induced deletion of Smad1 (S1^−/−) and Smad1/Smad5 (S1/5^−/−). (B) Lineage distribution in BM (left), PB (middle), and spleen (right) of induced mice (B cells; B220, T cells; CD3, and myeloid cells; Mac-1). Data are mean ± SD (n = 7 for WT, 3 for S1^−/−, and 4 for S1/5^−/−). *P < .05, **P < .001. represent WT; , S1^−/−; and ▬, S1/5^−/−. (C) Pathologic changes in the colon submucosa of S1/5^−/− mice (right) compared with WT (left; original magnifications ×100). (D) Spleen weights are mean ± SD (n = 7) (left), representative spleens from WT and S1/5^−/− mice (right). (E) Representative histologic photographs of WT (left) and enlarged S1/5^−/− spleens (right; original magnifications ×100). The arrows indicate the red pulp of the spleen.