Master 2
Mécanorécepteurs Artificiels

This internship will address the general problem of mechanotransduction by which all living organisms convert mechanical stimuli into a biological response. These biological processes are at the heart of human digital touch, where deformations and vibrations of the skin’s fingertips are conveyed to the somatosensory cortex by specialized neurons called mechanoreceptors.

Microscopically, it is known that the mechanoreceptors’ ability to measure mechanical cues relies primarily on the presence of assemblies of stress-activated ion channels in the plasma membrane. These channels are transmembrane nanometric protein pores whose stress-induced conformational changes modify the ion membrane permeability. The resulting ion fluxes across the membrane cause its depolarization, which in fine can trigger action potentials. Mammalian mechanoreceptors are characterized by striking fast response capabilities to time varying mechanical stimuli (frequencies ~100 Hz) and some of them even possess unique band pass-like frequency responses. How such characteristics relate to the specifics of protein pores responses is still far from being understood. The existence of a static mechanical response threshold itself is still unclear, as well as the relationship between a dynamical mechanical excitation and the pores open/closed states temporal distribution. To what extent is the pores’ dynamical response coupled to the viscoelastic properties of the soft layers surrounding the mechanoreceptors, and can it provide keys to understand the band pass-like characteristics of mammalian mechanoreceptors?

To address these questions, we are currently developing minimal model systems that are biomimetic of the functioning of mechanoreceptors, using synthetic lipid bilayers decorated with mechanosensitive (MS) protein channels and stimulated mechanically in a controlled manner. As lipid bilayer systems, we are using Droplet Interface Bilayers (DIB) obtained by putting into contact two aqueous compartments bathing in an oil-lipid mixture. To produce MS proteins, we are using a cell free transcription/translation (TX-TL) system that allows to express proteins in vitro. A preliminary setup has already been implemented in our group, consisting of a hydrogel droplet in contact with a hydrogel slab (see graphical abstract above). Using electrophysiology techniques, we have performed our first measurements of the ionic current when the DIB is decorated with passive pores.

For this internship, we propose to probe the ionic transport through the DIB decorated with the MS MscL protein found in E. coli bacteria using electrophysiology and eventually calcium imaging that offers spatially resolved measurements. Mechanical stimulation using a piezoelectric transducer will have to be implemented. We will then probe the response of the MS DIB to oscillating uniaxial stresses, measure the temporal distributions of the open/closed states of MscL, and study their dependence with the viscoelastic properties of the hydrogel.

The student involved in this internship will acquire experimental skills in ultra-low current electrophysiological, calcium imaging and mechanical measurements, in vitro protein expression, microfabrication, image processing and data analysis. He/she will also benefit from interactions with V. Noireaux (Univ. of Minnesota, USA) for the TX-TL systems, J. Mathé (Univ. of Evry-Val d’Essonne) for the electrophysiology aspects, and R. Voituriez and A.-F. Bitbol, both at LJP, for the theoretical aspects of the project. Finally, pursuit of this internship with a PhD thesis will also be possible.

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