Fig. 2. Microscopic and histological assessment of physical defects in MLC2a-null embryos. Whole embryo assessment of wild-type (A) and MLC2a-null (G) mouse embryos at somite pairs 24. Note that the null mutant displays severe chest edema. Paraffin wax-embedded serial sections of wild-type (B-F) and MLC2a-null (H-L) mouse embryos were stained for nuclei and cytoplasm with Hematoxylin and Eosin, respectively. White arrows point out the lack of mesenchymal cell seeding in atrioventricular cushions of MLC2a mutant (K), in contrast to normal mesenchymal cell seeding in atrioventricular cushions of wild-type control (E). Black arrows in D and J indicate dilated ventricle. A, atria; OT, outflow tract; RA, right ventricle; LA, left atria; RV, right ventricle; LV, left ventricle; SV, sinus venosus.