biostudies-literatureAdhyapok PNational Institutes of Health102317https://www.ebi.ac.uk/biostudies/studies/S-EPMC8050378biostudies-literatureUnknown24(4)Somitogenesis is often described using the clock-and-wavefront (CW) model, which does not explain how molecular signaling rearranges the pre-somitic mesoderm (PSM) cells into somites. Our scanning electron microscopy analysis of chicken embryos reveals a caudally-progressing epithelialization front in the dorsal PSM that precedes somite formation. Signs of apical constriction and tissue segmentation appear in this layer 3-4 somite lengths caudal to the last-formed somite. We propose a mechanical instability model in which a steady increase of apical contractility leads to periodic failure of adhesion junctions within the dorsal PSM and positions the future inter-somite boundaries. This model produces spatially periodic segments whose size depends on the speed of the activation front of contraction (<i>F</i>), and the buildup rate of contractility (Λ). The Λ/<i>F</i> ratio determines whether this mechanism produces spatially and temporally regular or irregular segments, and whether segment size increases with the front speed.iScienceA mechanical model of early somite segmentation.PMC8050378U01 GM111243R01 GM076992R01 GM077138Clendenon SGPiatkowska AMStern CDBelmonte JMNorman MJGlazier JAAdhyapok PfalseA mechanical model of early somite segmentation.Somitogenesis is often described using the clock-and-wavefront (CW) model, which does not explain how molecular signaling rearranges the pre-somitic mesoderm (PSM) cells into somites. Our scanning electron microscopy analysis of chicken embryos reveals a caudally-progressing epithelialization front in the dorsal PSM that precedes somite formation. Signs of apical constriction and tissue segmentation appear in this layer 3-4 somite lengths caudal to the last-formed somite. We propose a mechanical instability model in which a steady increase of apical contractility leads to periodic failure of adhesion junctions within the dorsal PSM and positions the future inter-somite boundaries. This model produces spatially periodic segments whose size depends on the speed of the activation front of contraction (<i>F</i>), and the buildup rate of contractility (Λ). The Λ/<i>F</i> ratio determines whether this mechanism produces spatially and temporally regular or irregular segments, and whether segment size increases with the front speed.2021-01-01T00:00:00Z2021 Apr2024-11-15T19:54:42.044Z2022-02-09T15:56:46.059ZS-EPMC80503783388981610.1016/j.isci.2021.102317