Content area
Full Text
The segmented body plan of vertebrates is established during somitogenesis, a well-studied process in model organisms; however, the details of this process in humans remain largely unknown owing to ethical and technical limitations. Despite recent advances with pluripotent stem cell-based approaches1-5, models that robustly recapitulate human somitogenesis in both space and time remain scarce. Here we introduce a pluripotent stem cell-derived mesoderm-based 3D model of human segmentation and somitogenesis-which we termed 'axioloid'-that captures accurately the oscillatory dynamics of the segmentation clock and the morphological and molecular characteristics of sequential somite formation in vitro. Axioloids show proper rostrocaudal patterning of forming segments and robust anterior-posterior FGF-WNT signalling gradients and retinoic acid signalling components. We identify an unexpected critical role of retinoic acid signalling in the stabilization of forming segments, indicating distinct, but also synergistic effects of retinoic acid and extracellular matrix on the formation and epithelialization of somites. Comparative analysis demonstrates marked similarities of axioloids to the human embryo, further validated by the presence of a Hox code in axioloids. Finally, we demonstrate the utility of axioloids for studying the pathogenesis of human congenital spine diseases using induced pluripotent stem cells with mutations in HES7 and MESP2. Our results indicate that axioloids represent a promising platform for the study of axial development and disease in humans.
(ProQuest: ... denotes formulae omitted.)
Previous studies have enabled the reconstruction of the human segmentation clock in vitro1,4'6. However, these systems have lacked the ability to form proper axial segmental organization, a central feature of all vertebrates, limiting their utility for the understanding of higher-order tissue organization and more advanced stages of human embryonic development. As supplementation of extracellular matrix (ECM) molecules in vitro has been shown to facilitate the formation of higher-order tissue structures in organoids as well as help mimic morphogenetic processes in mouse pluripotent stem cell-derived gastruloids2 and trunk-like structures3, we set out to establish a single germ layer, mesoderm-based 3D model of human axial development using human induced pluripotent stem (iPS) cells. We exposed iPS cells in a step-wise manner to signals promoting primitive streak and presomitic mesoderm (PSM) fates (Fig. 1a and Methods). The spontaneously symmetry-breaking and elongating mesodermal aggregates (Fig. 1b, Extended Data Fig. 1a and Supplementary Video 1) were then embedded into...