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Formation of the posterior commissure in the developing zebrafish embryo
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Resumo(s)
We aimed to study the development of the tract of the posterior commissure (TPC) in the early zebrafish
embryo. Even though TPC anatomy has been described, its development has yet to be explored. The TPC
is conserved in vertebrates and connects the right and left parts of the brain, in the diencephalonmesencephalon region. In the zebrafish, it has been linked to interhemispheric communication and binocular
integration. The Lx200 transgenic line, created in the laboratory, was used, since it expresses fluorescent
proteins in neuronal subpopulations, including in the TPC and the ventral caudal cluster (vcc), whose
neurons project along this tract.
We determined that the Lx200 transgenic line labels a subcluster of the vcc, the Lx200-vcc, with projections
pioneering TPC development, at around 20 hpf. The location of the Lx200-vcc was determined as ventral,
in the prosomere 1 (p1)-mesencephalon region, while proper TPC was located in the p1. In situ hybridization
assays to observe the known expression pattern of genes allowed for this localization. At larval stages, the
TPC location was similar, close to the dorsal midline in the p1 region, while somas were located in the p1-
mesencephalon region, both were determined via photoconversion of the Dendra2 protein.
Dendra2 photoconversion also allowed for the determination of Lx200-vcc cells' contribution to the tracts.
Rostral Lx200-vcc cells project along the TPC, but not to the medial-longitudinal fascicle (MLF), while
caudal Lx200-vcc cells likely contribute to the MLF.
Whole mount in vivo lightsheet and confocal imaging allowed for a qualitative and quantitative description
of the process of TPC formation. We utilised the Imaris image analysis software to trace and track the
projections in time. TPC development occurred via non-turning, branching projections, in a ventral to dorsal
direction. Connections occurred via the contact of opposing growth cones or by growth cone-axon
connections.
We provide a detailed characterization of the Lx200-vcc neurons and of TPC development. Our work
contributes to a deeper understanding of axonogenesis, a major step in central nervous system development,
in a whole embryo context. Future work will focus on the molecular pathways responsible for TPC
development.
Descrição
Tese de mestrado, Biologia Evolutiva e do Desenvolvimento, 2023, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
circuitos neuronais formação da comissura peixe zebra Teses de mestrado - 2023