Smooth Muscle Cell Markers in Developing Rat Lung

We employed a panel of antibodies directed against cytoskeletal and contractile proteins in a developmental study to follow the differentiation and distribution of smooth muscle-like cells in the rat lung. We observed that, in the mesenchyme around developing airways and vessels, desmin replaces vimentin as the predominant intermediate filament as specialization toward smooth muscle occurs. Normally, desmin and smooth muscle myosin were expressed together in the cells and their acquisition appeared indicative of terminal differentiation of smooth muscle. In this regard, the maturation of vascular smooth muscle is delayed in the lung relative to that surrounding the developing air passages. α-smooth muscle actin-containing cells form a thicker coat around the primitive airway tubes and extend farther down the tree than desmin or smooth muscle myosin-positive cells. This suggests that the α-actin is a marker for initial differentiation of smooth muscle cells and that these cells arise from the enveloping me...