Biocomplexity Institute, Indiana University, Bloomington, IN 47405, USA; Department of Physics, Indiana University, Bloomington, IN 47405, USA; Corresponding author
Agnieszka M. Piatkowska
Department of Cell and Developmental Biology, University College London, London WC1E 6BT, United Kingdom
Michael J. Norman
Department of Physics, North Carolina State University, Raleigh, NC 27607, USA; Quantitative and Computational Developmental Biology Cluster, North Carolina State University, North Carolina, USA
Sherry G. Clendenon
Biocomplexity Institute, Indiana University, Bloomington, IN 47405, USA; Department of Intelligent Systems Engineering, Indiana University, Bloomington, IN 47405, USA
Claudio D. Stern
Department of Cell and Developmental Biology, University College London, London WC1E 6BT, United Kingdom
James A. Glazier
Biocomplexity Institute, Indiana University, Bloomington, IN 47405, USA; Department of Intelligent Systems Engineering, Indiana University, Bloomington, IN 47405, USA
Julio M. Belmonte
Department of Physics, North Carolina State University, Raleigh, NC 27607, USA; Quantitative and Computational Developmental Biology Cluster, North Carolina State University, North Carolina, USA
Summary: 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 (F), and the buildup rate of contractility (Λ). The Λ/F ratio determines whether this mechanism produces spatially and temporally regular or irregular segments, and whether segment size increases with the front speed.
