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Embryonic Cell Sorting and Movement
Differential cell adhesion has long been thought to drive cell sorting. Maître et al. (p. 253, published online 23 August) show that cell sorting in zebrafish gastrulation is triggered by differences in the ability of cells to modulate cortex tension at cell-cell contacts, thereby controlling contact expansion. Cell adhesion functions in this process by mechanically coupling the cortices of adhering cells at their contacts, allowing cortex tension to control contact expansion. In zebrafish epiboly the enveloping cell layer (EVL)—a surface epithelium formed at the animal pole of the gastrula—gradually spreads over the entire yolk cell to engulf it at the end of gastrulation. Behrndt et al. (p. 257) show that an actomyosin ring connected to the epithelial margin triggers EVL spreading both by contracting around its circumference and by generating a pulling force through resistance against retrograde actomyosin flow.
Abstract
Differential cell adhesion and cortex tension are thought to drive cell sorting by controlling cell-cell contact formation. Here, we show that cell adhesion and cortex tension have different mechanical functions in controlling progenitor cell-cell contact formation and sorting during zebrafish gastrulation. Cortex tension controls cell-cell contact expansion by modulating interfacial tension at the contact. By contrast, adhesion has little direct function in contact expansion, but instead is needed to mechanically couple the cortices of adhering cells at their contacts, allowing cortex tension to control contact expansion. The coupling function of adhesion is mediated by E-cadherin and limited by the mechanical anchoring of E-cadherin to the cortex. Thus, cell adhesion provides the mechanical scaffold for cell cortex tension to drive cell sorting during gastrulation.
