At low density (LD), TAZ (red) is nuclear and SMAD3 (green) is cytoplasmic. TGF-β receptors are distributed throughout the cell surface. In response to TGF-β, SMAD3 accumulates in the nucleus where TAZ is located. At high density (HD), TAZ is excluded from the nucleus, as a result of cell density sensing. In non-polarized cells, TGF-β induces SMAD3 nuclear accumulation, while TAZ remains cytoplasmic. In polarized cells (schematically represented with apical villi), apical delivery of TGF-β is without effect on SMAD localization because TβRs are exclusively basolateral and TGF-β access to its receptors is blocked by intercellular junctions.