The three-sided romance of the lateral line: glia love axons love precursors love glia.

The lateral line system of fish and amphibians is closely related to the inner ear in terms of evolution, morphology and physiology. Several recent papers have shed new light on the postembryonic development of this system, and have revealed an unexpected triangular relationship where migrating sensory precursors guide axons, axons guide glia and glia, in turn, control the formation of sensory organs. They have also revealed the crucial importance of controlled cell migration not only for patterning the system, but also for determining polarity (and therefore directional sensitivity) of the mechanosensory hair cells. The remarkable accessibility of the lateral line system may allow a detailed analysis of cell migration and polarization, and may help us better understand the complex interactions between sensory precursor cells, neurons and glia during development.