GSE132478
Mesenchymal proteases and tissue fluidity remodel the extracellular matrix during airway epithelial branching in the embryonic avian lung
Reciprocal signaling between an epithelium and its surrounding mesenchyme is common during morphogenesis. These epithelial-mesenchymal interactions are particularly evident in tissues that undergo branching morphogenesis, such as the airway epithelium of the lung. Here, we found that reciprocal interactions between the epithelium and mesenchyme drive remodeling of the extracellular matrix (ECM) during morphogenesis of the embryonic chicken lung. RNA-Seq analysis revealed changes in the expression of genes associated with integrin signaling and ECM remodeling. Consistently, we found that prior to branching, the basement membrane is a spatially uniform sheath that wraps the airway epithelium. After branch initiation, however, the basement membrane is significantly depleted from the tip of extending branches. Culturing embryonic lung explants revealed that this basement membrane thinning is mediated by matrix metalloproteinase-2 (MMP2), which is expressed in the mesenchyme. Inhibiting MMP activity suppresses branch extension but has no effect on branch initiation. As branches extend, we found that tenascin-C (TNC) accumulates in the mesenchyme several cell diameters away from the branch tip. Despite its pattern of accumulation, this mesenchymal ECM protein is expressed exclusively by airway epithelial cells, which activate focal adhesion kinase (FAK) to induce TNC expression. We found that branch extension coincides with the deformation of adjacent mesenchymal cells into elongated geometries, which correlates with an increase in the fluidity of the mesenchyme at branch tips. This local increase in mesenchymal movement transports TNC from the epithelial surface into the mesenchyme. These data reveal novel epithelial-mesenchymal interactions that direct ECM remodeling during airway branching morphogenesis. Overall design: Three biological repilcates from two different stages of chicken lung development (E5 and E6, a total of six samples) were used in this analysis. Fold changes in transcript levels between E5 and E6 lungs were generated referencing transcript counts in E5 lungs.