Excitable dynamics of the segmentation clock*

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.