Compressive stress regulates tissue compaction through BMP signaling. (A) Percentage of cells positive for pSmad1 and pSmad5 in HH25 cushions cultured under osmotic stress for 24 h, n=4 or 5, data are mean±s.d. (B) Compaction trend for compressive stress combined with the Alk2/3 inhibitor LDN. (C) Compaction trend for BMP treatment combined with the Alk2/3 inhibitor LDN, n=4 or 5 cushions per condition, data are mean±s.e.m. (D) Representative immunofluorescence images stained for pSmad1/5 of HH25 cushions cultured under osmotic stress over 24 h. T, tensile stress; U, unloaded; C, compressive stress. Arrowhead indicates an example of a pSmad1/5-positive cell. Scale bar: 50 μm, **P<0.01 [ANOVA with Tukey's post-hoc test (A,C) and a two-tailed unpaired t-test (C)].