You were once a hollow shell. To sculpt that hollow ball into an
organism with layers of internal organs, muscle and skin, portions of
that embryonic 'shell' folded inwards.
The same happens to fruit fly embryos, and researchers at the European
Molecular Biology Laboratory (EMBL) in Heidelberg, Germany, have now
identified a particular group of cells which are crucial for the first
such fold. They also showed for the first time that the shape in which
cells are arranged determines the direction in which they contract.
Published Nov.19 in Developmental Cell, the findings were obtained
thanks to a new technique in which the scientists use a laser as a remote control.
When a fruit fly embryo is around 4 hours old, cells on its underside
start contracting, making the tissue fold inwards to form what is known
as the ventral furrow. Inside each cell, a network of actin fibres pulls
the membrane inwards, taking it from a roughly round shape to a
rectangle that gets thinner and thinner, and pulls its neighbours into
the embryo as it contracts.
The EMBL scientists developed a new technique in which they use a laser
to remove anchor points for the actin fibres, preventing individual
cells from contracting. By applying the technique to different parts of
the embryo, they were able to pinpoint a cluster of cells that have to
contract for the ventral furrow to form. The same approach enabled them
to outline an area in the embryo and prevent cells outside that region
from contracting. By changing the shape of the 'contracting' area, they
discovered that cells only contract like they do in normal embryos if
they are arranged in a rectangle. This implies that the 'squashing' from
circular to rectangular shape is not directed by some internal
programming but rather is dictated by the overall shape of the tissue.
The new approach overcomes one of the main challenges scientists have so
far faced when studying development: it enables them to view effects
immediately. By contrast, the standard methods to date, which relied on
turning genes on or off, required hours or even days before the effects
of that manipulation could be seen.
"The methods we had available so far made it a bit like arriving at the
scene of a car crash after the fact: you know something went wrong at
some point, but you were not there when it happened, so you cannot tell
what exactly caused the accident," says Stefano De Renzis, who led the
work. "Our new optogenetic method is more like a remote control: you
turn on the laser, and see the effect within seconds."
Next, De Renzis plans to use this new method to look at how cells in the
developing fruit fly embryo communicate with each other.
The technique has already raised considerable interest. The EMBL
scientists have received requests from colleagues looking to apply to
studies of stem cells and neural tube development in mice, as well as
others investigating fruit fly development, interactions between cells,
and more.
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Source: http://en.ofweek.com/news/Lasers-used-to-prevent-cells-from-contracting-36636
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