The organisation of cellular proteins and structures into organised periodic patterns is common in biology, and has been studied extensively on the level of cells and tissues, but less so on subcellular scales. Now, Huimin Zhang and colleagues (Wang et al., 2020) reveal how, in the C. elegans epidermis, the periodic subcellular framework, which is composed of various cytoskeletal, structural and signalling proteins, is formed and maintained during epidermal morphogenesis. They show that spectrin and actin are the first proteins to display the periodic striped pattern, and that the organisation of other factors was lost in the absence of either protein, indicating that both are essential for stripe formation. The maintenance of this pattern during post-embryonic development, however, depends on hemidesmosomes. During the elongation of the epidermal syncytium, stripes duplicate by first thickening and then splitting apart. Thickening occurs through the random addition of new hemidesmosomes into existing stripes, whereas splitting is the result of extension forces arising from epidermal growth acting on physical links between stripes to separate them. These links are likely provided by collagens, as in their absence the even spacing of stripes becomes disrupted during the duplication process. Collectively, these results provide new insight into the formation and maintenance of periodic subcellular patterns, which might be relevant to other elements of cell growth and tissue development.
