ERK-mediated Curvature Feedback Regulates Branching Morphogenesis in Lung Epithelial Tissue

Abstract

Intricate branching patterns emerge in internal organs because of the repetitive presence of simple deformations in epithelial tissues. During murine lung development, epithelial cells in distal tips of a single tube require fibroblast growth factor (FGF) signals generated by their surrounding mesenchyme to form repetitive tip bifurcations. However, it remains unknown how the cells employ FGF signaling to convert their behaviors to achieve the recursive branching processes. Here we show a self-sustained epithelial regulatory system during the murine lung branching morphogenesis, mediated by extracellular signal-regulated kinase (ERK), which acts as a downstream driver of FGF signaling. We found that tissue-scale curvature regulates ERK activity in the lung epithelium using two-photon live cell imaging and mechanical perturbations. ERK is activated specifically in epithelial tissues with a positive curvature, regardless of whether the change in curvature was attributable to morphogenesis or artificial perturbations. Moreover, we found that ERK activation accelerates actin polymerization specifically at the apical side of cells, and mechanically contributes to the extension of the apical membrane, leading to a decrease in epithelial tissue curvature. These results indicate the existence of a negative feedback loop between tissue curvature and ERK activity beyond scale. We confirmed that this regulation was sufficient to generate the recursive branching processes by a mathematical model. Taken together, we propose that ERK mediates the curvature feedback loop underlying the process of branching morphogenesis in developing lungs.

3D cell neighbour dynamics in growing pseudostratified epithelia

“…As the cell nuclei move along the apical-basal axis during the cell cycle ( Meyer et al, 2011 ), the cytoplasm fills the remaining space between the apical and basal surfaces, likely in a way that minimises the total surface area of all cells. The determinants of the epithelial thickness, that is, the distance between the apical and basal surfaces are still unknown, but signalling downstream of Fibroblastic Growth Factor (FGF), Sonic Hedgehog (SHH), Bone Morphogenetic Protein (BMP)/ transforming growth factor-beta (TGF-β), and WNT has been observed to affect cell height, presumably via an effect on cell tension and/or cell-cell adhesion ( Gritli-Linde et al, 2002 ; Hirashima and Matsuda, 2021 ; Kadzik et al, 2014 ; Kondo and Hayashi, 2015 ; Widmann and Dahmann, 2009 ).…”

Tracheal Ring Formation

“…Non-canonical SHH signaling has been suggested to trigger calcium-induced extracellular signal-regulated kinases (ERK) activation Robbins et al (2012) ; Carballo et al (2018) . ERK may also respond to pressure and/or curvature, as reported for the lung epithelium Hirashima and Matsuda (2021) . In epithelial cells from the mammary gland, ERK activity has been found sensitive to the stiffness of the surrounding matrix Farahani et al (2021) .…”

RTK signalling promotes epithelial columnar cell shape and apical junction maintenance in human lung progenitor cells

“…S9D for phospho-antibody validation experiments). In the pseudoglandular mouse lungs, pERK is predominantly expressed in the distal epithelia (Hirashima and Matsuda, 2022; Jiang et al, 2018; Liu et al, 2004; Tang et al, 2011) and pAKT can be detected in the epithelial cells (Wang et al, 2005; Yin and Ornitz, 2020). However, there was sample-to- sample variation in pERK and pAKT staining in human embryonic lungs.…”