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Title: From somites to vertebral column
Author: Ward, E.
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2016
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Vertebrates build their bodies in segments. This segmentation is established in the embryo when the paraxial mesoderm becomes segmented into the somites, which contain the precursors of the axial skeleton (sclerotome) and muscles (dermomyotome). The number and size of somites, and later the morphology of the vertebrae they go on to form, are both thought to be determined by information intrinsic to the paraxial mesoderm. This has led to the general understanding that the final segmental pattern of the vertebral column is a direct read-out of the segmentation established during somitogenesis. This study explores the role of signals external to the somite in segmentation of the vertebral column. Using fluorescent markers, the fate of somites was traced from anterior-posterior along the chick vertebral column, revealing a regionspecific shift between the dorsal and ventral sclerotome, possibly mediated by external signals during sclerotome migration. Next, I identify the notochord as a potential source of these signals, and show that the notochord is required for segmentation of the vertebral bodies. Furthermore, an ectopic notochord is sufficient to alter the spatial periodicity of sclerotome set up in the somites. Inter-regional notochord grafts and somite tracing suggests that this change in somite segmentation is achieved by a previously unidentified attraction of the sclerotome towards the notochord, which compresses somitic segments. I go on to test whether Sonic hedgehog signalling from the notochord provides a directional cue by attracting sclerotome cells to the midline. This study indicates that a role for the notochord in vertebral segmentation is present in amniotes, highlighting a much-overlooked aspect of the development and evolution of vertebral patterning.
Supervisor: Stern, C. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available