Abstract

Gastruloids, which model formation of the primary body axis of vertebrate embryos, turn themselves from spheres into rods, breaking symmetry to organise cell rearrangements known as convergent extension (CE). Gastruloid elongation demonstrates that CE is, or can be, entirely self-organising, and that self-organising mechanisms are embedded in this, and likely others of the many instances of CE in development. Classically, self-organisation in biology involves Turing Reaction-Diffusion (RD) patterning by diffusible morphogens. We have explored the possibility that a completely different, non-RD-based, self-organisation principle for symmetry-breaking by CE could exist, namely polarity-propagating mechanical feedback, for which there is experimental evidence at the single-cell level. Using in silico modelling, we show that extremely simple rules for mechanical interactions are sufficient to organise convergent extension. Thus, although Turing himself chose to consider only chemical morphogenesis, mechanical self-organisation seems likely to be involved in CE, either orthogonal to RD or providing a form of “double assurance” (robustness-enhancing redundancy).

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