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Asymmetry plays a major role in biology at every scale: think about the spirals of DNA, the human heart is positioned to the left, our preference for using our left or right hand … The Valrose Institute of Biology Institute (CNRS / Inserm / Université Côte d'Azur), in collaboration with colleagues from the University of Pennsylvania, showed how a single protein induces a spiral motion in another molecule. By the domino effect, this causes the cells, organs and indeed the whole body to twist, triggering lateral behavior. This research is published in the journal Science on November 23, 2018.
Our world is fundamentally asymmetrical: think of the double helix of DNA, the asymmetric division of stem cells, or the human heart being positioned on the left … But how do these asymmetries occur and are they interconnected?
At the Valrose Institute of Biology, the team led by CNRS researcher Stéphane Noselli, including Inserm and Université Cote d'Azur, studied for many years the left-right asymmetry to solve these puzzles. Biologists had identified the first asymmetry of gene control in the common fruit fly (Drosophila), one of the organisms of the biologist's preferred model. More recently, the team has shown that this gene plays the same role in vertebrates: the protein it produces, Myosin 1D, controls the wrapping or rotation of organs in the same direction.
In this new study, the researchers induced the production of Myosin 1D in the symmetrical normal organs of Drosophila, such as the respiratory trachea. Quite spectacularly, this was enough to induce asymmetry at all levels: the deformed cells, the trachea wrapped around them, the twisting of the whole body, and the helical behavior of the locomotives among the fowl larvae. Remarkably, these new asymmetries are always developing in the same direction.
To identify the origin of these cascading effects, biochemists from the University of Pennsylvania contributed to the project: on a glass case, they brought Myosin 1D into contact with a component of the cytoskeleton (the "vertebral column" of the cell), namely actin. They could see that the interaction between the two proteins caused the actin to spiral.
In addition to its role in the left-right asymmetry between Drosophila and vertebrates, Myosin 1D appears to be a unique protein that is capable of inducing asymmetry itself and at all levels, first at the molecular level, then through a domino effect, cell, tissue, and behavioral level. These results suggest a possible mechanism for the sudden appearance of new morphological characteristics during evolution, such as, for example, the twisting of snail bodies. Thus, Myosin 1D appears to have all the features necessary for the emergence of this innovation, since its expression alone is sufficient to induce twisting at all levels.
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