In the nervous system, certain mRNAs are transported along axons and show localised translation. This is thought to be important for axon-autonomous regulation of, for example, growth cone turning and guidance. However, we still have an incomplete understanding of which mRNAs are localised, how their transport and translation are controlled, and how this impacts neuronal development and function. The IMP1 RNA-binding protein is known to play a role, particularly in controlling local expression of β-actin in neurons and other cell types, and John Flanagan and colleagues (p. ) now investigate the function of its relative IMP2. In the developing mouse nervous system, IMP2 shows specific localisation to axon tracts. Identification and analysis of the mRNAs to which IMP2 binds reveals a large number of putative targets, including many associated with axon guidance, cell migration and cytoskeletal organisation. Consistent with this, IMP2 knockdown in the developing chick spinal cord leads to growth cone stalling and failed axon midline crossing at the floor plate. This phenotype is reminiscent of loss of one of the identified IMP2 targets, namely the Robo1 receptor, whose axonal protein levels are reduced upon IMP2 knockdown. Together, these data identify a new player in axonal mRNA regulation and provide a valuable dataset for further analysis of the role of IMP2 and its targets.
