Neuronal differences prefigure somatotopy in the zebrafish lateral line.

The central projection of the fish lateral line displays somatotopic ordering. In order to know when and how this ordering is established, we have labelled single sensory neurones and followed the growth of their neurites. We show that the neuromast cells and the corresponding neurones are not related by a fixed lineage, and also that somatotopic differences between anterior and posterior line neurones, and among neurones of the posterior line, are present before innervation of the sense organs. We propose that the position of the central projection defines the peripheral position that the neurone will innervate.