Spiral cleavage – the process by which cells of the early embryo divide and spiral around the pole-to-pole axis of the embryo – is the most common mode of animal development. Many hypotheses exist to explain how the precise spatial arrangement of cells is coordinated during this process, but to date there has been no systematic approach to verify which, if any, of these hypotheses are true. Now, on p. 54, Isaac Salazar-Ciudad and colleagues construct a computational framework in order to simulate early spiral cleavage behaviour. Using this model, they are able to constrain the behaviour of cells with existing hypotheses so as to determine which are important for the emergence of spiral cleavage and which are not. The authors find that none of the hypotheses proposed over time can produce the precise arrangement of cells observed during spiral cleavage, but that a small subset of them can do so if combined. Specifically, animal-vegetal polarization of cell division, Sachs’ rule in which cell division is oriented perpendicularly to the previous cell division, cortical rotation and adhesion are the main contributing variables to spiral cleavage. Finally, the authors show that their model can be used to generate a range of different embryo geometries corresponding to what is seen in seven different spiralian species. This elegant study highlights the power of computational approaches in understanding developmental processes, and brings insight into the specific parameters that govern spiral cleavage.
- © 2017. Published by The Company of Biologists Ltd