Control of Mitotic Spindle Angle by the RAS-Regulated ERK1/2 Pathway Determines Lung Tube Shape

During early lung development, airway tubes change shape. Tube length increases more than circumference as a large proportion of lung epithelial cells divide parallel to the airway longitudinal axis. We show that this bias is lost in mutants with increased extracellular signal-regulated kinase 1 (ERK1) and ERK2 activity, revealing a link between the ERK1/2 signaling pathway and the control of mitotic spindle orientation. Using a mathematical model, we demonstrate that change in airway shape can occur as a function of spindle angle distribution determined by ERK1/2 signaling, independent of effects on cell proliferation or cell size and shape. We identify sprouty genes, which encode negative regulators of fibroblast growth factor 10 (FGF10)-mediated RAS-regulated ERK1/2 signaling, as essential for controlling airway shape change during development through an effect on mitotic spindle orientation.