In the developing mouse eye, the presumptive lens and retinal epithelia stay in close contact whilst undergoing a coordinated indentation movement known as invagination. The mechanisms that underlie this invagination event have remained mysterious, although cytoplasmic processes between the two epithelia were described as early as 1902. Now, on , Richard Lang and colleagues identify filopodia as being the processes present between these two epithelia, extending mainly from the presumptive lens. Their formation,they report, depends on Cdc42, IRSp53 and FAK, three molecules previously implicated in filopodia generation and anchoring. Using pharmacological inhibitors, the authors reveal that the filopodia can contract through the actin-myosin system and that this contractility regulates the distance between lens and retinal epithelia, as well as the depth of the lens pit. They conclude that the filopodia act as physical tethers that allow lens and retinal invagination to proceed in a coordinated fashion. Future work should address whether this mechanism of invagination occurs elsewhere during vertebrate morphogenesis.
