Setting the Tempo in Development

Setting the Tempo in Development: An Investigation of the Zebrafish Somite Clock Mechanism

Francois Giudicelli, Ertugrul M. Ozbudak, Gavin J. Wright, Julian Lewis

The of the are clocked out sequentially from the (PSM) at the tail end of the embryo. Formation of each somite corresponds to one cycle of oscillation of the somite segmentation clock—a system of genes whose expression switches on and off periodically in the cells of the PSM. We have previously proposed a simple mathematical model explaining how the oscillations, in zebrafish at least, may be generated by a delayed negative feedback loop in which the products of two target genes, and , directly inhibit their own transcription, as well as that of the gene for the Notch ligand ; Notch signalling via DeltaC keeps the oscillations of neighbouring cells in synchrony. Here we subject the model to quantitative tests. We show how to read temporal information from the spatial pattern of stripes of gene expression in the anterior and in this way obtain values for the biosynthetic delays and molecular lifetimes on which the model critically depends. Using transgenic lines of zebrafish expressing her1 or her7 under heat-shock control, we confirm the regulatory relationships postulated by the model. From the timing of somite segmentation disturbances following a pulse of her7 misexpression, we deduce that although her7 continues to oscillate in the anterior half of the PSM, it governs the future somite segmentation behaviour of the cells only while they are in the posterior half. In general, the findings strongly support the of how the somite clock works, but they do not exclude the possibility that other oscillator mechanisms may operate upstream from the her7/her1 oscillator or in parallel with it.

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  1. […] No Comments Le dernier post de PZ Myers (23/06/2007) tombe à pic après la lecture de Setting the Tempo in Development. Merde, si les gradients de morphogènes sont présents dans l’oeuf […]

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