Protein clue to biological asymmetry


Researchers identify a gene that makes organisms go all twisty. Nick Carne reports.


The movement of a normal fruit fly larva (left) and one expressing Myosin 1D in its normally symmetrical epidermis. The modified larva is twisted and moves via directional ‘barrel rolls.’

The movement of a normal fruit fly larva (left) and one expressing Myosin 1D in its normally symmetrical epidermis. The modified larva is twisted and moves via directional ‘barrel rolls.’

Gaëlle Lebreton / iBV / CNRS

A single protein can make you do the twist, new research suggests.

A study led by Stéphane Noselli from the Institute of Biology Valrose (iBV) in Nice, France, reveals how the specific protein induces a spiral motion in another molecule, which, in fruit fly at least, turn causes the entire body to twist, triggering lateralised behaviour.

The team has been investigating this for some time as it grapples with the bigger question of why asymmetry plays such a major role in biology.

Despite common assumptions to the contrary, asymmetry is extremely common at every level of biological organisation, from the chirality – or “handedness” of the DNA double helix, to the position of the mammalian heart, to body shapes such as that of fiddler crabs.

Noselli and colleagues want to know how these asymmetries emerge and if they are linked to one another.

Initially they identified the first gene controlling asymmetry in the common fruit fly (Drosophila) and showed that the protein it produces, Myosin 1D, controls the coiling or rotation of organs in the same direction. Next, they showed that this gene plays the same role in vertebrates.

In the latest study, reported in a paper published in the journal Science, the researchers induced the production of Myosin 1D in normally symmetrical organs of Drosophila, such as the respiratory trachea.

Quite spectacularly, they say, this was enough to induce asymmetry at all levels: deformed cells, trachea coiling around themselves, the twisting of the whole body, and helicoidal locomotive behaviour among fly larvae. And these new asymmetries always develop in the same direction.

To identify the origin of these cascading effects, they called in biochemists from the University of Pennsylvania in the US, who brought Myosin 1D into contact with actin, a component of the cell’s cytoskeleton or backbone. They observed that the interaction between the two proteins caused the actin to spiral.

The conclusion drawn is that Myosin 1D appears to be a unique protein capable of inducing asymmetry in and of itself: first at the molecular level, then, through a domino effect, at the cell, tissue, and behavioural level.

This suggests a possible mechanism for the sudden appearance of new morphological characteristics over the course of evolution, such as the twisting of snails' bodies.

Myosin 1D thus appears, the researchers say, to have all the necessary characteristics for the emergence of this innovation, since its expression alone suffices to induce twisting at all scales.

  1. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1420-9101.2006.01175.x
  2. http://dx.doi.org/10.1126/science.aat8642
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