Coming to Consensus: A Unifying Model Emerges for Convergent Extension

Abstract

Cell motility is a widespread biological property that is best understood in the context of individual cell migration. Indeed, studies of migration in culture have provided tremendous insight into the signals and mechanics involved and have laid the foundation for our understanding of similar migrations by larger cellular collectives. By contrast, our understanding of another flavor of movement, cell intercalation during convergent extension, is only now emerging. Here, we integrate divergent findings related to intercalation in different settings into a unifying model, paying attention to how this model does and does not resemble current models for directed cell migration.

Figure 1.

Cell migration differs from cell intercalation. A. Individual cell migration involves traction against an ECM and actin (red) assembly in the leading and lagging edges. B. In the “crawling” model for cell intercalation, initially set forth in mesenchymal cells, mediolaterallydirected (here, horizontal) protrusions act in a manner analogous to leading edges to drive mediolateral intercalation by cell crawling. C. In the “junction shrinking” model for cell intercalation, initially set forth in epithelial cells, movement is driven by actomyosin-mediated shrinkage of mediolaterally-aligned cell-cell junctions.

Figure 2.

A unified model for cell intercalation during convergent extension. Panels A-C represent successive stages of intercalation, in which apically-localized junction shrinking and basolateral cell crawling act in concert. The model is based on work from Williams et al., 2014 and Sun et al., 2017. Herein, we suggest that mesenchymal cells also exploit a hybrid model, though how the cell crawling and junction shrinking are spatially organized remains poorly defined.