Project description:This is the simple model without diffusion described in th epublication Sharp developmental thresholds defined through bistability by antagonistic gradients of retinoic acid and FGF signaling. Goldbeter A, Gonze D, Pourquié O. Dev Dyn. 2007 Jun;236(6):1495-508. PMID: 17497689, doi:10.1016/j.jtbi.2008.01.006 Abstract: The establishment of thresholds along morphogen gradients in the embryo is poorly understood. Using mathematical modeling, we show that mutually inhibitory gradients can generate and position sharp morphogen thresholds in the embryonic space. Taking vertebrate segmentation as a paradigm, we demonstrate that the antagonistic gradients of retinoic acid (RA) and Fibroblast Growth Factor (FGF) along the presomitic mesoderm (PSM) may lead to the coexistence of two stable steady states. Here, we propose that this bistability is associated with abrupt switches in the levels of FGF and RA signaling, which permit the synchronized activation of segmentation genes, such as mesp2, in successive cohorts of PSM cells in response to the segmentation clock, thereby defining the future segments. Bistability resulting from mutual inhibition of RA and FGF provides a molecular mechanism for the all-or-none transitions assumed in the "clock and wavefront" somitogenesis model. Given that mutually antagonistic signaling gradients are common in development, such bistable switches could represent an important principle underlying embryonic patterning. Originally created by libAntimony v1.4 (using libSBML 3.4.1) This model originates from BioModels Database: A Database of Annotated Published Models (http://www.ebi.ac.uk/biomodels/). It is copyright (c) 2005-2011 The BioModels.net Team. For more information see the terms of use. To cite BioModels Database, please use: Li C, Donizelli M, Rodriguez N, Dharuri H, Endler L, Chelliah V, Li L, He E, Henry A, Stefan MI, Snoep JL, Hucka M, Le Novère N, Laibe C (2010) BioModels Database: An enhanced, curated and annotated resource for published quantitative kinetic models. BMC Syst Biol., 4:92.

Project description:Pluripotent stem cells (PSCs) have increasingly been used to model different aspects of embryogenesis and organ formation. Despite recent advances in the in vitro induction of major mesodermal lineages and mesoderm-derived cell types experimental model systems that can recapitulate more complex biological features of human mesoderm development and patterning are largely missing. Here, we utilized induced pluripotent stem cells (iPSCs) for the stepwise in vitro induction of presomitic mesoderm (PSM) and its derivatives to model distinct aspects of human somitogenesis. We focused initially on modeling the human segmentation clock, a major biological concept believed to underlie the rhythmic and controlled emergence of somites, which give rise to the segmental pattern of the vertebrate axial skeleton. We succeeded to observe oscillatory expression of core segmentation clock genes, including HES7 and DKK1, determined the period of the human segmentation clock to be around five hours and showed the presence of dynamic traveling wave-like gene expression within in vitro induced human PSM. We furthermore identified and compared oscillatory genes in human and murine PSC-derived PSM, which revealed species-specific as well as common molecular components and novel pathways associated with the mouse and human segmentation clocks. Utilizing CRISPR/Cas9-based genome editing technology, we then targeted genes, for which mutations in patients with segmentation defects of vertebrae (SDV) such as spondylocostal dysostosis (SCD) have been reported (e.g. HES7, LFNG, DLL3 and MESP2 DLL3). Subsequent analysis of patient-like knock-out and point-mutation lines as well as patient-derived iPSCs together with their genetically corrected isogenic controls revealed gene-specific alterations in oscillation, synchronization or differentiation properties, validating the overall utility of our model system, to provide novel insights into the human segmentation clock as well as diseases associated with the formation of the human axial skeleton.

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Controlling human organoid symmetry breaking reveals signaling gradients drive segmentation clock waves

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