A Mechanical Model of Early Somite Segmentation

Priyom Adhyapok^1,2*, Agnieszka M Piatkowska³, Michael J Norman^4,5, Sherry G Clendenon^1,6, Claudio D Stern³, James A Glazier^1,6, Julio M Belmonte^4,5*

*Correspondence: priyom.adhyapok@gmail.com, jbelmon2@ncsu.edu

Accepted March 2021, iScience

doi: https://doi.org/10.1016/j.isci.2021.102317

Abstract

The clock-and-wavefront model (CW) hypothesizes that somite formation results from the interplay of molecular oscillations with a caudally-progressing front in the pre-somitic mesoderm (PSM), but does not explain how these signals modulate cell rearrangement into somites. Our Scanning Electron Microscopy analysis of chicken embryos reveal an epithelialization front of 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 periodic failure of adhesion junctions within the dorsal PSM and positions the future inter-somite boundaries. This model can produce spatially periodic segments whose size depends on the speed of the activation front (F) of contraction, and the build-up 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 as in CW model.

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Affiliations

¹ Biocomplexity Institute, Indiana University, Bloomington, IN, 47405, United States of America.

² Department of Physics, Indiana University, Bloomington, IN, 47405, United States of America.

³ Department of Cell and Developmental Biology, University College London, London, WC1E 6BT,

United Kingdom.

⁴ Department of Physics, North Carolina State University, Raleigh, NC, 27607, United States of America.

^v Quantitative and Computational Developmental Biology Cluster, North Carolina State University, USA.

⁶ Department of Intelligent Systems Engineering, Indiana University, Bloomington, IN, 47405, United

States of America.