Immunolocalization of FMOD (green, A-F), BGN (green, G-L), Col1a1 (green, M-R), and Col6 (green, S-X) in Fmod+/+ (A, C, E, G, I, K, M, O, Q, S, U, W) and Fmod−/− (B, D, F, H, J, L, N, P, R, T, V, X) mitral leaflet attachments. White boxes in A, B, G, H, M, N, S, T are magnified in panels C, D, I, J, O, P, U, V respectively. Yellow boxes in A, B, G, H, M, N, S, T are magnified and shown in E, F, K, L, Q, R, W, X respectively. Red- propidium iodide (PI); blue- α-sarcomeric actin (αSarc); IVS-interventricular septum; AS- atrial septum; MV- mitral valve; LA- left atrium; solid lines- distinct separation of MV and LA; dashed lines- diffuse attachment of left atrial to MV. Scale bars: A= 400μm applies to B, G, H, M, N, S, T; C= 50μm applies to D-F, I-L, O-R, U-X.