Distal pulmonary cell proliferation is associated with the expression of EIIIA+ fibronectin in the developing rat lung.

Fibronectin is known to regulate the development of the lung. The EIIIA segment of fibronectin is one of the major alternatively spliced segments and modulates the cell proliferative potential of fibronectin in vitro. But the specific role of the EIIIA-containing fibronectin isoform (referred to as EIIIA+ fibronectin) in pulmonary cell proliferation has not been explored in vivo as yet. In this study, to see whether EIIIA+ fibronectin is associated with pulmonary cell proliferation in vivo, the authors immunohistochemically examined the spatiotemporal relationship of the EIIIA+ fibronectin isoform protein and proliferating cell nuclear antigen (PCNA), a biochemical marker for the cell proliferation, during the alveolar formation in the developing rat lung. EIIIA+ fibronectin protein was localized in the epithelial cells and in the mesenchymal tissues. The expression of EIIIA+ fibronectin protein gradually decreased from the pseudoglandular stage to the saccular stage and then slightly increased from the saccular stage to the alveolar stage. This change in the EIIIA+ fibronectin expression seemed to be in accord with the change in the number of PCNA-positive cells in the distal pulmonary cells throughout the lung development. These results suggest that the expression of EIIIA+ fibronectin is associated with the distal pulmonary cell proliferation during the alveolar formation.