Supernumerary neuromasts in the posterior lateral line of zebrafish lacking peripheral glia.

The lateral line and its associated sensory nerves develop from cephalic epithelial thickenings called neurogenic placodes. In the zebrafish, the transcription factor neurogenin 1 is essential for the generation of the sensory ganglion from the placode, but is dispensable for the migration of the primordium and the initial development of neuromasts. We find that inactivation of the gene encoding neurogenin 1 leads to the development of over twice the normal number of neuromasts along the posterior lateral line of zebrafish larvae. Mutation of the gene encoding another transcription factor, sox10, has a similar effect. After a normal number of proneuromasts is initially deposited by the migrating primordia, interneuromast cells divide and differentiate to form the extra neuromasts. Our results indicate that the development of these intercalary neuromasts occurs principally because of the absence of neural crest-derived peripheral glia, which evidently inhibit the assembly of interneuromast cells into neuromasts.