Guide cells help navigate axon regeneration

During embryonic development, neurons project nascent axons that navigate through space to find their targets. Axonal-growth paths forged by these pioneer axons depend on chemical and physical cues from cells that can include guidepost cells, which directly interact with nascent axons and induce them to grow, stop, or turn (1). A series of guidepost cells can serve as “stepping stones” to organize the complex growth of an axon in space (2, 3). Although guidepost cells direct axon formation during embryonic development in diverse model organisms, their existence often is transient. Thus, it was unclear whether guidepost-like cells promote axon regeneration and whether regenerative guidepost cells are constitutive or induced by injury. On page 1447 of this issue, Scimone et al. (4) pinpoint regenerative guidepost-like cells in the visual system of freshwater flatworms called planarians.