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Somites Without a Clock

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Science  09 Jan 2014:
1247575
DOI: 10.1126/science.1247575

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Abstract

The formation of body segments (somites) in vertebrate embryos is accompanied by molecular oscillations (“segmentation clock”). Interaction of this with a wave travelling along the body axis (the “clock-and-wavefront model”) is generally believed to control somite number, size and axial identity. Here, we show that a clock-and-wavefront is unnecessary for somite formation. Non-somite mesoderm treated with Noggin generates many somites that form simultaneously, without cyclic expression of Notch-pathway genes, yet have normal size, shape and fate. These somites have axial identity: the Hox-code is fixed independently of somite fate. However they are not subdivided into rostral and caudal halves, necessary for neural segmentation. We propose that somites are self-organizing structures whose size and shape is controlled by local cell-cell interactions.

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