Investigating H1 horizontal cell development in the larval zebrafish retina

The proper functioning of the vertebrate central nervous system (CNS) depends on the precision by which specific neuronal cell classes establish appropriate synaptic connections. This is possible through crucial mechanisms that operate during development, when distinct neuronal cell classes are generated, differentiate to acquire specific morphological characteristics, migrate to their definitive locations and contact their correct synaptic partners. This is particularly evident in the retina, an accessible part of the CNS. The retina is a well-characterized neural network located at the back of the eye that transforms incoming photons of light into electrochemical signals used to generate vision. It is a highly organized structure and the only sensory tissue that houses two synaptic layers before information is transmitted to the brain, an architecture that facilitates the study of neuronal connectivity. Furthermore, several retinal cell types are spatially arranged in non-random planar patterns, known as mosaics, which reflect underlying circuit assembly mechanisms. My thesis aimed to investigate the development of H1 horizontal cells, a sub-type of neuron in the retina. I used Danio rerio (zebrafish) as a model organism as it is a vertebrate and can thus provide insights into vertebrate retinal development. Taking advantage of transgenic fish that fluorescently label H1 horizontal cells and their progenitors as well as the external, rapid development of zebrafish embryos, I conducted confocal-based in vivo time-lapse imaging to follow the generation and migration of these cells. Moreover, in flat-mount preparations of the retina, I examined the spatial organization of H1 horizontal cells and their connectivity to different subtypes of transgenically labeled cone photoreceptors.