Professor Olivier Pourquié, Harvard Medical School

Abstract:
The periodic segmentation of the vertebrate body axis into somites, and later vertebrae, relies on a genetic oscillator (the segmentation
clock) driving the rhythmic activity of signaling pathways in the presomitic mesoderm (PSM). While the clock is often presented as a population of phase-entrained oscillators, whether its oscillations are an intrinsic property of individual cells or represent a population-level phenomenon is not known. We show that oscillations are a collective property of PSM cells which can be actively triggered in vitro by a dynamical quorum sensing signal. We demonstrate that manipulation of mechanical cues is sufficient to predictably switch isolated PSM cells from a quiescent to an oscillatory state in vitro, a behavior reminiscent of excitability in other systems. Together, our work argues that the segmentation clock behaves as an excitable system, introducing a novel paradigm to study such dynamics in vertebrate morphogenesis.