Rohon-Beard Neuron in Zebrafish

We experience various sensations through our skin. The sensations are received by distinct sensory channels that are expressed in the trigeminal ganglion (TG) or the dorsal root ganglion (DRG). TG neurons innervate the head skin, whereas DRG neurons innervate the skin of the trunk and limbs. In addition to these neuronal populations, larvae of anamniote vertebrates (lampreys, teleosts, and amphibians) have an additional sensory neuronal population that develops prior to functional maturation of DRG neurons, termed Rohon-Beard (RB) neurons. RB neurons innervate the trunk skin; thus, the TG and RB neurons are responsible for larval somatosensation. After the maturation of DRG neurons, the physiological roles of the RB neurons are replaced progressively by the DRG neurons. Studies of somatosensation in zebrafish have suggested that the transition from RB neurons to DRG neurons is completed within 5 days post fertilization. During this transition, the RB neurons undergo programmed cell death; thus, RB neurons have been considered to be a transient neuronal population. However, recent studies using zebrafish have indicated that some RB neurons survive for at least 2 weeks post-fertilization. These long-lived RBs are distinguished by Protein Kinase C-α (PKCα) expression and comprise <40% of the RB population although their physiological significance remains to be elucidated. Furthermore, RB neurons show diversity in gene expression other than the PKCα gene, implying that there are several different cell types in RB neurons. However, the physiological significance of this diversity also remains unclear. Visualization of the neural activity and functional manipulation could contribute to greater insight into RB neuron physiology. Many genetic tools that enable the visualization and manipulation of cell activity have been introduced to zebrafish biology. In addition, some enhancer or promoter sequences that induce gene expression in specific subtypes of RB neurons have been isolated. Using these molecular tools, researchers can investigate the physiology of distinct RB neurons. Here, We focus on RB neurons, presenting a current understanding of their development, diversity, and function and methods for their manipulation and visualization.