Delayed Coupling Theory of vertebrate segmentation

LUIS G. MORELLI; SAÚL ARES; FRANK JÜLICHER

Max Planck Institute for the Physics of Complex Systems, Scientific Report 2009-2010

Typostudio Schumacher Gebler Dresden

Año: 2011; p. 52 - 53

The body plan of all vertebrate animals has a segmented organization that is reflected in the repeated arrangement of vertebra and ribs. This structure forms during the development of the organism by a process called segmentation. The segments —called somites— form sequentially along a linear axis, one by one, with a precisely controlled timing. The timing of vertebrate segmentation is set by a genetic clock. This clock is realized by oscillations of the levels of certain proteins in individual cells. The genes encoding for these proteins are called cyclic genes. Their expression changes periodically in time. The genetic oscillations of cells in the tissue are coordinated by a molecular signaling system that introduces a coupling between neighboring cellular oscillators. This gives rise to a collective spatio-temporal pattern which consists of waves that travel and eventually stop and arrest in a periodic arrangement of somites. Signaling gradients ranging over larger distances control the slow down and arrest of the cellular oscillators and guide spatio-temporal patterns during segmentation. The segmentation process can be studied on different levels of organization that range from molecular and cellular to tissue length scales. We have developed a theoretical description of somitogenesis based on a coarse grained representation of cellular oscillators as phase oscillators. Our study of the collective self-organization of coupled genetic oscillators during segmentation highlights the importance of time-delays in the coupling. These time-delays arise because of the slow dynamics of signaling processes that couple neighboring cells. The resulting delayed coupling theory can be compared to quantitative experiments. This allows us to identify key principles of cellular coordination during vertebrate morphogenesis.