Meeting Abstract
The optical clarity, extensive genetic toolkit, and small size of the larval zebrafish make it amendable to explorations of neuromechanical form and function. Here, we apply these approaches to investigate the sensory architecture of the pectoral fin and consider its relationship to function. We mapped the full extent of the sensory innervation of the fin, the first time this has been done in the limb of a vertebrate. We stochastically labeled the mechanosensory Rohon-Beard cells (RBs) by injecting UAS:ptagRFP into isl2b:Gal4 embryos, imaged these at 5dpf with confocal microscopy, and reconstructed single neurons. We found that a subpopulation of islet2B+ RBs located at the level of the fourth and fifth myomeres innervate the pectoral fin. These cells display classic RB morphology with dense primary afferent arborization. Unexpectedly, RBs that innervate the fin also innervate the body. In the fin, RB processes innervate abductor, adductor, or occasionally both surfaces of the skin. The degree of innervation of the fin varied between RBs, with some cells branching to cover a large area of the fin while others projected into smaller regions only at the base. We hypothesized that there would be increased innervation at the level of the blood vessel, a previously described point of bending where the musculature at the base of the fin gives way to the membranous distal portion of the fin; however, we find no evidence of increased density in the bending “joint.” The variation of innervation fields within the fin, in combination with axial innervation, suggests a complexity of sensory information processing at the level of single RBs and across the population. This work provides a basis for more direct interrogation of function as well as possible comparative studies between vertebrates and invertebrates.
