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Diversity of visual projections in vertebrates

Abstract : The sole output of the eye are the retinal ganglion cells (RGCs) that project into multiple brain nuclei via the optic nerve (ON). A key choice point for RGC axons is to decussate at the midline to project either ipsi-laterally or contra-laterally. The first aim of this thesis is to evaluate whether the narrow set of molecules regulating RGC decussation is evolutionarily conserved. Secondly, we strive for a finer understanding of specific axon guidance molecules by using conditional mutant mice. To this end, we design a novel clearing tool (EyeDISCO) to access the entire visual system in three dimensions, from the eyes to the brain proper. First, we uncover that ipsi-lateral retinal projections (IRPs) are present in the first ray-finned fish as well as lobe-finned fish. These results suggest that IRPs most likely emerged in the common vertebrate ancestor. We further show that the molecular program orchestrating IRPs is not evolutionarily conserved in a ray-finned species. This hints at the fundamental idea that other cues may be responsible for the guidance of IRPs. Second, we shed light on the role of Dcc/Netrin-1 in RGC projections of mice. Remarkably, while a significant subset of RGC axons are unable to project into the ON, we reveal that a large population of RGCs still manages to project correctly in the absence of Dcc and Netrin-1. This heterogeneity underlines the probable interplay of multiple other, still undiscovered, guidance cues. Together, our work proposes a more complex model for RGC targeting across species and warrants future studies to take on an evolutionary perspective to better understand the fundamental mechanism at play during axon guidance.
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Submitted on : Wednesday, October 13, 2021 - 4:50:13 PM
Last modification on : Friday, October 15, 2021 - 3:41:36 PM

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  • HAL Id : tel-03376769, version 1

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Robin Vigouroux. Diversity of visual projections in vertebrates. Neurobiology. Sorbonne Université, 2020. English. ⟨NNT : 2020SORUS363⟩. ⟨tel-03376769⟩

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