BNR #51 by Dr. Charlie GOSSE (LPN-CNRS, France) Sept. 26th,2013 @ PM5:00- E-lounge

Dr. Charlie Gosse

Laboratoire de Photonique et de Nanostructures, LPN-CNRS, Marcoussis, France

Magnetic and electric microsystems for the spatiotemporal modulation of biological signaling pathways



Cell-fate decisions and cellular functions are dictated by the spatiotemporal dynamics of regulation

cascades. Similarly, at the scale of an entire organism, especially during its development, molecular signaling

networks ensure interactions between different cell groups, conveying information that orders for instance to

migrate, differentiate, proliferate, or die.

To understand this kind of phenomena one usually relies on a perturbative approach: the concentration

of a signaling molecule is modulated in space and time and molecular mechanisms are inferred from the

response of the biological system. Along those lines, we will here introduce two microfluidic tools that we have

developed in collaboration with chemists and biologists. They address questions at both the cell and the

organism scales.

First, we have focused on the Ran/RCC1 reaction network responsible for the assembly of the mitotic

spindle. Microtubule regulators were conjugated to magnetic particles and the application of a magnetic field

enabled to concentrate them, yielding a spatiotemporal step input. As the threshold enabling nucleation was

thus locally exceeded, microtubule polymerization and aster formation were soon observed. A reactiondiffusion

model accounting for the recorded response could next be validated thanks to computer simulations.

Second, we were interested in how the anterior-posterior polarity is established in the mouse embryo

at early post-implantation stages, between 5 and 6 days of development. Since morphogens such as Nodal

play a key role in this process, we have fabricated a microdevice to electroporate nucleic acids in small cell

populations and therefore achieve corresponding gene over-expression or knock down (thanks to pDNA or

siRNA, respectively). At the moment a chip has been devised with the help of finite element model simulations.

It includes dielectric guides that both localize the effect of the applied potential drop and guarantee the

embryo survival. During preliminary experiments we have defined optimal electrical conditions by systematically

evaluating the size of the permeabilized territories and the cellular viability. Subsequently, transgenes

coding for fluorescent proteins could be reproducibly introduced in only a few cells and live imaging provided

new insights on the coordinated migration of the distal visceral endoderm in anterior position