Examining refinement of the early touch-response circuit in zebrafish neurodevelopment

During early development, the central and peripheral nervous systems are characterized by exuberant cells, projections, and synapses that are later pruned away to homeostatic levels. This pruning allows for tissue morphogenesis, regulation of cell populations, error correction, and optimization of neural connectivity. For neural circuits, this facilitates the establishment of rudimentary circuits which necessitate early organism survival and allow for later refinement. However, little is known about how these fundamental, developmental mechanisms lead to a nervous system precisely tuned for efficient behaviors, survival, and learning. In this dissertation, I first review these developmental concepts in relation to the importance of cell clearance. Then, I present my investigation into circuit refinement in the context of an early-formed touch-response circuit in zebrafish. I demonstrate surprising and strong evidence that contradicts previous studies: an essential component of the touch-response circuit, Rohon-Beard neurons, does not succumb to developmental programmed cell death. This work unveils new questions on the function of these surviving Rohon-Beard neurons and their effects on the dynamics and physiology of somatosensory processing.