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How embryos scale vertebrae

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Researchers take a step closer to decoding how cells coordinate embryonic growth
Published: 21 Dec 2012

As embryos develop and grow, from a single-cell egg to a fully functional body, they must form organs that are in proportion to the overall size of the embryo. The exact mechanism underlying this fundamental characteristic, called scaling, is still unclear. But researchers from the European Molecular Biology Laboratory in Heidelberg, Germany, and McGill University in Montreal are one step closer to understanding it.

The researchers have discovered that scaling of the future vertebrae in a mouse embryo is controlled by how the expression of certain genes oscillates, in a coordinated way, between neighbouring cells. The findings, published in Nature, highlight the importance of this oscillatory pattern in ensuring that embryos grow up to becoming well-proportioned animals.

 

Neighbouring cells in the future vertebrae column of an embryo coordinate to turn specific genes on and off in turn, generating a wave of gene expression similar to the ‘Slide to unlock’ animation on a smart phone. To study this process, and determine its impact on how proportions of the future vertebrae are maintained, the researchers developed a new technique.

“Using this new assay, we were able to film this wave of gene expression in real time with high precision, and to identify whether this pattern could change according to the overall size,” explains Alexander Aulehla who coordinated the study at EMBL Heidelberg. “There is a clear link: when the embryo is smaller, the number of segments formed remains the same, but each segment is smaller and the expression waves are proportionally slower.”

The speed of the wave seems to be the essential characteristic to predict the size of the future vertebra: the faster the wave, the bigger the vertebrae. Similar expression waves have been observed in several vertebrates and also in insect species, so this communication pattern among embryonic cells seems to be widespread. However, scientists haven’t yet elucidated how the speed of the wave is controlled at a molecular level.

Paul François, an assistant professor of Physics at McGill, collaborated with the EMBL research team by writing a computer model of what happens in the tissue.  “What surprised me is that you can reproduce the complex behavior with a relatively simple, three-parameter mathematical model. This suggests mechanisms that maybe tested in the future to understand how embryonic cells coordinate with each other to ensure formation of properly sized vertebrae.”

Francois’s research focuses on the modeling of physical properties of gene networks and their evolution – a field that has emerged at the nexus of biology and physics in recent years, following sequencing of the human genome and rapid growth in scientists’ understanding of the processes inside cells.

To view the film of gene expression in an embryo: http://youtu.be/T-fa1gYfwJk

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