A new role for Sonic Hedgehog signalling in morphogenesis of the spinal cord = Nuevas funciones de la vía de señalización Sonic Hedgehog en la morfogénesis de la médula espinal
[eng] Development of the posterior spinal cord involves secondary neurulation, a process poorly understood in which neural tube is formed by cavitation of the tail bud. Comprehension of secondary neurulation is required to understand the morphogenetic origin of high prevalence neural tube defects su...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2015 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/99504 |
| Acceso en línea: | https://hdl.handle.net/2445/99504 http://hdl.handle.net/10803/385723 |
| Access Level: | acceso abierto |
| Palabra clave: | Medul·la espinal Marcadors tumorals Spinal cord Tumor markers |
| Sumario: | [eng] Development of the posterior spinal cord involves secondary neurulation, a process poorly understood in which neural tube is formed by cavitation of the tail bud. Comprehension of secondary neurulation is required to understand the morphogenetic origin of high prevalence neural tube defects such as spina bifida. In zebrafish embryos neurulation goes through a stage of neural rod; a neural primordium that hollows a lumen in the middle. To form a single continuous lumen, cells converge to the tissue center, divide in stereotyped orientations perpendicular to it (the so-called C-Divisions), and form a tissue midline composed by apical polarity components that will later originate the central lumen. Polarizing events start with the centrosomes positioning in the midline under the control of unknown cues. Sonic Hedgehog has been widely described as a midline signaling protein in other systems, and its components are located in the apical cilium and the underlying basal body, formed by a centrosome. Shh expression onset occurs during gastrulation in embryonic midline structures —notochord and floor plate- and maintained along neurulation, suggesting a role of Shh in neural tube morphogenesis. Treatment with the Shh inhibitor cyclopamine disrupts the lumina! surface, while Shh pathway activation (Shh-GOF) produces partial to total lumen duplication. Shh-LOF/Shh-GOF display defects in neural lumen positioning and/or formation, confirming a role of Shh in lumen formation. Shh-LOF and Shh-GOF preserve their apicobasal polarity and tissue architecture. Analysis of the dynamics of tissue convergence in ShhGOF embryos shows that compared to the same WT stages the neural plate is wider and the neural plate borders stop converging later in development, suggesting delayed cell convergence movements. However comparison between Shh-GOF and WT cell trajectories to the midline reveals no differences in motion. We found that trajectories of cells committing C-Divisions had indistinguishable motion properties compared to their neighbouring cells, and that Shh-GOF cellular motion properties —velocity and persistency- are resistant to Shh activity. We next analyzed the behaviour of dividing cells and observed that mitosis progressively lengthened along neurulation. Detailed analysis of the mitotic phases shows that Shh-GOF cells show shortened mitoses from condensation to anaphase, but spend the same time –or slightly longer- in metaphase. C-Divisions need orient their metaphase plate so they divide perpendicularly to the midline, giving rise to daughter cells that lie at the sides of the prospective lumen. In C-Divisions, metaphase plate rotations are decreased and slower. We next assessed if division orientation was compromised along neural tube formation. Analysis of division orientation shows higher variability in ShhGOF embryos especially at early stages, a fact that would have morphogenetic consequences in the C-Divisions and lumen formation. With similar cell motion properties and similar metaphase duration between WT and ShhGOF mitotic cells, the latter have quicker mitoses, less metaphase rotations and the stereotyped orientation of polarizing C-Divisions is altered, thereby affecting lumen formation. |
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