A unified mechanism for spatiotemporal patterns in somitogenesis

Somitogenesis, the process of body segmentation during embryonic development, exhibits a key set of features that is conserved across all vertebrate species despite differences in the detailed mechanisms. Prior to the formation of somites along the pre-somitic mesoderm (PSM), periodic expression of clock genes is observed in its constituent cells. As the PSM expands through the addition of new cells at its posterior, the oscillations in the cells closer to the anterior cease and eventually lead to formation of rostral and caudal halves of the somites. This pattern formation is believed to be coordinated by interactions between neighboring cells via receptor-ligand coupling. However, the mechanism underlying the transition from synchronized oscillations to traveling waves and subsequent arrest of activity, followed by the appearance of polarized somites, has not yet been established. In this paper we have proposed a unified mechanism that reproduces the sequence of dynamical transitions observed during somitogenesis by combining the local interactions mediated via Notch-Delta intercellular coupling with global spatial heterogeneity introduced through a morphogen gradient that is known to occur along the anteroposterior axis of the growing PSM. Our model provides a framework that integrates a boundary-organized pattern formation mechanism, which uses positional information provided by a morphogen gradient, with the coupling-mediated self-organized emergence of collective dynamics, to explain the processes that lead to segmentation.