Polarised epithelial cells become migratory during several developmental processes, taking on many mesenchymal characteristics. But what happens during migration to the proteins that establish and maintain epithelial cell polarity? Pinheiro and Montell show that epithelial cells need not lose their polarity during migration; indeed, polarity is sometimes required for proper motility (see p. 5243). The researchers investigate the migration of border cells in the Drosophila ovary, which move from the follicular epithelium to the oocyte. They show that the apical epithelial polarity proteins Par-6, Par-3/Bazooka and atypical protein kinase complex (aPKC) remain asymmetrically localised during border cell migration. Depletion or overexpression of Par-6 or Bazooka disrupts migration and causes the mislocalisation of membrane proteins, including E-cadherin. The researchers propose that the Par-3/Par-6/aPKC complex, as well as establishing polarity, may sometimes contribute to the invasiveness of epithelial cells during development, wound healing and tumourigenesis.
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