The cortical actomyosin cytoskeleton is a major
determinant of these mechanical properties. Yet, an integrated view linking the
biochemical properties of the cortex, the structures it assembles and cell
mechanics is still missing. We want to characterize how from the local
biochemical dynamics of the cortex in vivo emerges a
structured, active and dynamic polymer material that controls the cell
mechanics and morphogenesis.
For this, we use a small worm, the nematode C. elegans, an extremely powerful model system, combining
a variety of approaches from different fields: quantitative live cell imaging,
genetics, optogenetics, biophysics and biochemistry.
During the development of an embryo, each cell
plays its part in well-orchestrated ballet that shapes the organism. But to
shape the embryo, cells must tune their mechanical properties in a concerted
and tightly regulated manner.
A thin layer of a polymer at the cell surface, the cortex, is responsible in a
large part for defining cell mechanics, not unlike how the mechanics
of a balloon is defined by the nature of the plastic that makes it. And the mechanical
properties of this polymer come from the fibers it's made of, like
how the fabric of a shirt or a sweater makes it stiff or stretch.
in addition to these traditional properties, the cortex has two additional skills. First, it builds up and breaks down very rapidly:
it is dynamic. If you leave
a water balloon on a shelf and then decide a year later to pick it up again,
the same material would be there, the same polymer fibers. Same is true for the fabric of your shirt or your sweater. In the cortex, on the other
hand, a filament has a shelf life of seconds to minutes. Go take
a coffee for two minutes, come back: all the filaments that make it have been
replaced by new ones. This has a very important consequence the cortex is
visco-elastic. At short time scale, that is if you do something quick, it will
behave like a spring, we talk of an elastic material. But at long
time scales it behaves like a fluid. If you pull on it slowly, it will change
its shape and adjust to a new one, just like honey. The second skill of the
cortex is its ability to contract: it is active. The cortex is made
of filaments, like fibers in a plastic or a shirt, but also of miniature motor
that can contract. This gives rise to a very interesting property of the cortex:
it can actively shrink. Imagine your sweater shrinking in the back, while new
fabric is being weaved in the front, or your kid's waterballoon shrinking
on one end while new rubber forms on the other side. Well, that's
basically what happens to some cells as they migrate.
Our aim is to
understand how the assembly of the cortex, this dynamic and active polymer, controls cell