Abstract

Epithelial morphogenesis involves changes in cell shape and cell neighbors that result from forces exerted at cell-cell junctions. We discuss how these forces can drive formation of spatial patterns and alignment of cell polarity in developing multicellular epithelia. Specifically, we consider the process of global alignment in the chick auditory epithelium, which consists of two cell types, hair cells (HCs) with an asymmetric mechanosensory hair bundle at its apex and supporting cells (SCs). During development, these two cell types form a regular pattern, and the hair bundle of each HC aligns with the tissue axis. Through a combination of experiments and theory, we find that a force pattern generates both positional and orientational order on the tissue scale. Positional order is established by differences between the mechanical activity of cell-cell junctions. These differences are encoded by cell-specific genetic programs restricting the diphosphorylated form of non-muscle myosin-II regulatory light chain (RLC) to specific junctions. In addition, local attenuation of RLC phosphorylation by the hair bundle organizes supracellular patterns of myosin activity, which generates tissue-wide orientational order. Our findings show that junctional asymmetries couple cell rearrangements to polarity, which could be a general feature of development and repair in tissues consisting of different cell types.