A mechanical perspective on vertebral segmentation

Segmentation is a characteristic feature of the vertebrate body plan. The prevailing paradigm explaining its origin is the ‘clock and wave-front’ model, which assumes that the interaction of a molecular oscillator (clock) with a traveling gradient of morphogens (wave) pre-defines spatial periodicity. While many genes potentially responsible for these processes have been identified, the precise role of molecular oscillations and the mechanism leading to physical separation of the somites remain elusive. In this paper we argue that the periodicity along the embryonic body axis anticipating somitogenesis is controlled by mechanical rather than bio-chemical signaling. Using a prototypical model we show that regular patterning can result from a mechanical instability induced by differential strains developing between the segmenting mesoderm and the surrounding tissues. The main ingredients of the model are the assumptions that cell–cell adhesions soften when overstretched, and that there is an internal length scale defining the cohesive properties of the mesoderm. The proposed mechanism generates a robust number of segments without dependence on genetic oscillations.