Several developmental stages, including dorsal closure (DC), involve epithelial fusion events during which cell-cell adhesions disassemble, cells migrate and, when migration is complete, cell-cell adhesions reassemble. On p. , Nicholas Harden and colleagues reveal how the Scribble complex (which contains Scrib, a polarity regulator) and Pak (a Cdc42/Rac effector kinase; Cdc42 and Rac regulate actin-based membrane extensions during cell migration) interact to shift epithelial cells between adhered and migratory states in Drosophila. In mammalian cells, Scrib recruits Cdc42, Rac and Pak to the leading edge (LE) membrane during cell migration. Similarly, in Drosophila Pak localisation in the follicular epithelium is Scrib dependent. Importantly, however, the researchers show that during DC, Scrib is lost from the LE during epidermal migration, and, at the end of DC, integrin-localised Pak recruits the Scrib complex to the LE, thereby restoring apicobasal polarity and cell-cell adhesion. They suggest, therefore, that bidirectional interactions between the Scrib complex and Pak might modulate epithelial plasticity during DC and in other developmental situations.
