Title: New transgenic reporters identify somatosensory neuron subtypes in larval zebrafish Running Title: Larval zebrafish somatosensory neuron subtypes

To analyze somatosensory neuron diversity in larval zebrafish, we identified several enhancers from the zebrafish and pufferfish genomes and used them to create five new reporter transgenes. Sequential deletions of three of these enhancers identified small sequence elements sufficient to drive expression in zebrafish trigeminal and Rohon-Beard (RB) neurons. One of these reporters, using the Fru.p2x3-2 enhancer, highlighted a somatosensory neuron subtype that expressed both the p2rx3a and pkcα genes. Comparison with a previously described trpA1b reporter revealed that it highlighted the same neurons as the Fru.p2x3-2 reporter. To determine whether neurons of this subtype possess characteristic peripheral branching morphologies or central axon projection patterns, we analyzed the morphology of single neurons. Surprisingly, although these analyses revealed diversity in peripheral axon branching and central axon projection, PKCα/p2rx3a/trpA1b-expressing RB cells did not possess obvious characteristic morphological features, suggesting that even within this molecularly defined subtype, individual neurons may possess distinct properties. The new transgenes created in this study will be powerful tools for further characterizing the molecular, morphological, and developmental diversity of larval somatosensory neurons. Introduction Somatosensation is carried out by a variety of specialized populations of sensory neurons that detect different types of thermal, chemical and mechanical touch stimuli (Lumpkin and Caterina, 2007; Marmigère and Ernfors, 2007). Innervation of the skin by somatosensory neurons occurs very early in development, allowing animals to detect touch even at embryonic stages (Davies and Lumsden, 1984; Moore and Munger, 1989; Kimmel et al., 1990; Saint-Amant Page 2 of 42 John Wiley & Sons, Inc. Developmental Neurobiology