Mitotic polarity oscillation promotes epithelial tumor progression

Mitosis of epithelial cells requires a transient loss of epithelial polarity [1-5]. However, the nature of this mitotic polarity oscillation and its functional consequences for epithelial development are not fully understood. Here we show that the Crumbs (Crb) complex, a key regulator of epithelial polarity, is lost from the membrane during mitosis, and the Crb mutant phenotype is ameliorated when cell division is inhibited. Remarkably, an essential requirement of Crb for epithelial polarity is fully suspended when cell division is blocked in conjunction with inhibition of either cell ingression or cell intercalation. We conclude that the amount of morphogenetic stress induced by mitosis, ingression, and intercalation determines the requirement for Crb. Increased cell division and loss of cell polarity are two main drivers of epithelial cancer [6-8]. Maintaining epithelial polarity is important for limiting proliferation. Whether the loss of polarity during mitosis impacts tissue growth is less clear. We show that increasing cell division in a morphogenetically quiet epithelium not only increases tissue size but also causes hyperplastic to neoplastic transition. Conversely, reducing cell division restores epithelial polarity in neoplastic tissue of tumor mutants. Taken together, our study revealed that a major function of polarity factors in epithelial maintenance is to counteract morphogenetic stress. Moreover, we propose a feedforward mechanism that links cell division and the loss of polarity as a key driver of epithelial cancer.