Fig. 3

Mbnl1 ^E∆3/∆E3 mice have precocious EMT in the endocardial cushions without a persistent increase in total mesenchyme production. Close-up views of the hearts in sagittal sections of wild type E9.25 (a) and Mbnl1 ^∆E3/∆E3 E9 (b) embryos stained with H&E reveal precocious invasion of mesenchymal cells (red arrowhead) into the AVC cushions of knockout mice. Sections from three individuals were evaluated for each group; representative images are shown. Close-up views of the AVC cushions in adjacent sections from wild type E9.25 (c) and Mbnl1 ^∆E3/∆E3 E9 (d) embryos subjected to immunohistochemistry with an antibody against pSMAD2 reveal high levels of TGFβ signaling in only a few cells in wild type cushions (red arrowhead), but nearly all cells in the knockout cushions. H&E stained sagittal sections of wild type (e) and Mbnl1 ^∆E3/∆E3 (f) hearts do not reveal noticeable hypercellularity in the AVC cushions at E10.5. Atr = atrium, vent = ventricle, EC = endocardial cushion, OFT = outflow tract. g The average relative number of mesenchymal cells was determined by counting the cells within the AVC cushions on serial, H&E-stained, sagittal sections of wild type and Mbnl1 ^∆E3/∆E3 E10.5 embryos. Representative three-dimensional reconstructions of AVC cushions from optical sections of wild type (h) and Mbnl1 ^∆E3/∆E3 (i) E10.5 hearts imaged using optical coherence tomography. Videos of the optical sections and reconstructions of these hearts are shown in Additional file 2: Movie S1 and Additional file 3: Movie S2, respectively; still images shown here were rotated to the same viewing angle