The vertebrate body axis is subdivided into repeated segments, best exemplified by the vertebrae that derive from embryonic somites. The number of somites is precisely defined for any given species but varies widely from one species to another. To determine the mechanism controlling somite number, we have compared somitogenesis in zebrafish, chicken, mouse and corn snake embryos. Here we present evidence that in all of these species a similar ‘clock-and-wavefront’1,2,3 mechanism operates to control somitogenesis; in all of them, somitogenesis is brought to an end through a process in which the presomitic mesoderm, having first increased in size, gradually shrinks until it is exhausted, terminating somite formation. In snake embryos, however, the segmentation clock rate is much faster relative to developmental rate than in other amniotes, leading to a greatly increased number of smaller-sized somites.
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Sequences of genes described in this paper have been deposited into GenBank under accession numbers EU196456, EU196465, EU232010, EU196457, EU196458, EU196459, EU196460, EU196466, EU196461, EU196464, EU196462 and EU196463.
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The authors thank M. Gibson, B. Rubinstein, P. Francois and members of the Pourquié laboratory for critical reading and discussions, M. Wahl for the mouse LFNG pictures, members of the Reptile and Aquatics Department, J. Chatfield for editorial assistance, and S. Esteban for artwork. Research was supported by Stowers Institute for Medical Research, and in part by a Defense Advanced Research Projects Agency (DARPA) grant (O.P.). J.L. is supported by Cancer Research UK. Zebrafish were obtained from the Zebrafish International Resource Center (ZIRC) at the University of Oregon, which is supported by a grant from the NIH-NCRR. O.P. is a Howard Hughes Medical Institute Investigator.
Author Contributions C.G. and O.P. designed the experiments, C.G. cloned the snake genes and performed the mouse, chicken and snake in situ hybridizations, E.M.O. performed the fish in situs, C.G. and E.M.O. performed the measurements and analysed the data with O.P. D.B. established the corn snake and zebrafish colony and produced the embryos. C.G. and J.W. performed the cell cycle analysis. J.L. performed the mathematical modelling. C.G., E.M.O., J.L. and O.P. wrote the manuscript. All authors discussed the results and commented on the manuscript.
The file contains Supplementary Methods with additional references, Supplementary Figures 1-5 with Legends, Supplementary Tables 1-4 and Supplementary Boxes 1-2. (PDF 4543 kb)
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Gomez, C., Özbudak, E., Wunderlich, J. et al. Control of segment number in vertebrate embryos. Nature 454, 335–339 (2008). https://doi.org/10.1038/nature07020
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