| Abstract: |
| The formation of body segments (somites) in vertebrate embryos is accompanied by molecular oscillations (the segmentation clock). Interaction of this oscillator with a posterior-moving molecular gradient along the body axis is generally believed to control somite number, size, and axial identity according to the clock-and-wavefront model. We present simulations that replicate many observed features of segmentation based on these hypotheses. However, experiment using the differentiation inducer Noggin, show that the clock-and-wavefront mechanism is not necessary for somite formation and we present an alternative mechanical instability mechanism which also explains many of the observed features of somitogenesis. The moral is not that one mechanism is right and the other wrong. Rather, Occam`s Razor does not always apply in biology--in many cases fundamentally distinct mechanisms each of which would be independently sufficient, act simultaneously during development to build specific structures. |
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