Guided cell migration and postsynaptic membrane expansion (PME) are both important developmental processes, but much remains to be learned about their regulation. Now, Peter Roy and colleagues report that in C. elegansneuromuscular junction formation, during which muscle cells extend membrane processes called muscle arms towards the motor axons, several previously identified cell and axon guidance genes also direct PME (see ). In a genetic screen for mutants with fewer muscle arms, the authors identified 10 genes,including unc-40/Dcc, which encodes a transmembrane receptor that guides cell and axonal migration in response to UNC-6/Netrin. They find that UNC-40 is enriched in muscle arms and directs muscle arm extension to motor axons independently of UNC-6. Among the factors that lie downstream of UNC-40,the authors report, are the guanine-nucleotide exchange factor UNC-73/Trio,members of the WAVE actin-polymerisation complex and the focal adhesion component homologue UNC-95. Together, these data suggest that many genes required for guided cell and growth cone migration have related roles in directing PME.
