To assess the importance of secreted BMP antagonism in suppressingphysiological signaling in DSS colitis, we usedCagg-CreERT2;Grem1fl/flmice to knockout intestinal stromal Grem1 expression7,32 (Figure 5A).Although efficient recombination was seen in theαSMA-positive muscularis cells throughout the colon,WASCs continued to robustly express Grem1 in colonic ulcer beds(Figure 5B). Here, GREM1 is linked to colitis.