<i>Furin</i> mutant hearts show a decreased in the number of phospo-Smad positive cells at the AV junction.

(A-F) Immunostaining showing the expression of pSMAD1/5 (red), cTNI (green) and TBX3 (white) in the left atrioventricular junction of a E14.5 mouse heart. B, C, E, F show high magnifications of the areas squared in A and D. White arrowheads indicate phospho-SMAD1/5 positive / Tbx3 positive cells. Yellow arrowheads indicate phospho-SMAD1/5 positive epicardial derived mesenchymal cells of the AV sulcus. (G) Graph showing a significant reduction in the number of phospho-SMAD1/5 positive cells in the TBX3 positive population of the AV canal. (n = 3 hearts analysed for each genotype). *P<0.05 for unpaired Student’s t test. (H) Graph showing that the number of TBX3 positive cells in the AV junction is equivalent in wildtype and control. (I) Graph showing that the number of phospho-SMAD1/5 positive cells in the epicardial derived mesenchymal cells of the AV sulcus is equivalent in wildtype and control.