Control of Embryonic Lung Branching Morphogenesis by the Rho Activator, Cytotoxic Necrotizing Factor 1

Abstract

Background. Lung development is sensitive to physiological stresses, and its development may be impaired by physical distortion, as in patients with congenital diaphragmatic hernia. Yet, little is known about how mechanical forces can influence lung morphogenesis. Studies with cultured cells suggest that cytoskeletal tension may play a key role in growth control. Since the small GTPase Rho plays an important role in the control of cell tension generation, we carried out studies to test the hypothesis that changes in Rho-mediated cell tension may influence branching morphogenesis. Methods. Embryonic lung buds from timed pregnant Swiss Webster mice were microdissected on Embryonic Day 12 (E12), and whole organs were cultured in serum-free medium in the presence of the Rho activator cytotoxic necrotizing factor 1 (CNF-1) for 48 h. Serial measurements of the degree of epithelial branch formation and tissue maturation were performed using light microscopy and computerized image analysis. Results. At 48 h, embryonic lungs treated with 2 ng/ml CNF-1 increased their terminal bud count by 236 ± 18% ( P = 0.01) compared with 132 ± 2% for untreated controls. However, dose–response experiments revealed biphasic behavior: at a higher dose of CNF-1 (200 ng/ml), bud number was actually decreased relative to controls (43 ± 1%, P < 0.001). Histological analysis revealed that individual glands appeared to be more highly developed at low-dose CNF-1, whereas the high dose produced gland contraction. Conclusions. These data support a potential role for Rho and cytoskeletal tension in control of epithelial pattern formation during lung development.