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  • An evo-devo approach to vertebral body development: going back to progenitors
    Publication . Azevedo, Tomás Augusto Barreiros Pais de; Palmeirim, Isabel; Witten, Paul Eckhard; Andrade, Raquel P.
    The segmented signal for vertebral body development is conveyed, in zebrafish, through mineralization of the notochordal sheath and, in chicken, through resegmentation of the most medially located ventral sclerotome cells, with the contribution of the notochord still unclear. Along with the different size of the notochord in these two embryos, this leads to the hypothesis that evolutionary changes in the expression territories of transcription factors could underlie these differences. In the zebrafish axial(notochord)/paraxial(PSM/somite/sclerotome) mesoderm progenitor region, flh normally represses spt that normally defines paraxial mesoderm fate, leading to an axial mesoderm one instead. The aims of this thesis were to clarify the role of the notochord in chicken segmented vertebral body formation and investigate the role of transcription factor evolutionary changes in this process’s differences between zebrafish and chicken. In chapter II we thoroughly describe the first morphological landmark of segmented vertebrae, Von Ebner’s fissure, using it as a proxy to observe that the notochord and dermomyotome are not responsible for vertebral body segmented signal initiation. In chapter III, through CNOT2 electroporation experiments, we observe an increase in the axial mesoderm size (notochord and floor plate), accompanied by a shortening of axial length and downregulation of TBX6L. We conclude that CNOT2 represses TBX6L, leading axial/paraxial progenitor cells to assume an axial mesoderm cell fate. In chapter IV, we fill in a lingering chicken embryo knowledge gap, by producing a detailed quantification of early axis elongation. At the same time, we provide a reproducible and precise staging system and a morphometric tool to analyze experimental data. This thesis demonstrates the evolutionary shift in preponderance from the notochord to the PSM/somites/sclerotome in the role on segmented signal location and axial elongation. It also proposes that changes in the flh/CNOT2 and spt/TBX6L expression territories in the axial/paraxial mesoderm region are underlying these shifts.
    2022-07-11Doctoral thesis Embargo Show more