Thèse

Vendredi 10 Octobre 2025 à 14h00.

Probing molecular concentration in cell nuclei with Brillouin microscopy

Lucie VOVARD

Amphithéâtre Dirac, Bâtiment Dirac

Invité(e) par
DEHOUX Thomas, MONNIER Sylvain

présentera en 2 heures :

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Directeur de thèse / thesis director :
DEHOUX Thomas, MONNIER Sylvain

Membres du jury / jury members :
Mme. HELFER Emmanuèle - Directrice de Recherche CNRS,
M. DJEMIA Philippe - Professeur Université Sorbonne Paris Nord,
Mme. DELANOE-AYARI Hélène - Maître de Conférence Université Lyon 1,
Mme. ETIENNE-MANNEVILLE Sandrine - Directrice de Recherche CNRS,
M. GUEROUI Zoher - Directeur de Recherche CNRS

Résumé / Abstract :
Understanding the physical properties of biological matter represents a central challenge in biophysics. In this thesis, we explore the potential of Brillouin Light Scattering (BLS) microscopy, an optical, label-free, and non-invasive technique, for probing the acoustic properties of living cells. Brillouin scattering measures the frequency shift and linewidth broadening of Brillouin peaks, which are directly related to the speed of sound and acoustic attenuation in the sample, respectively. However, these quantities are inherently acoustic and thus depend on the sample’s dynamics; their interpretation requires an explicit rheological framework. After characterizing a three-dimensional Brillouin microscopy setup, we demonstrate that BLS measurements are sensitive to intracellular molecular concentration, notably through osmotic shocks that modulate cell volume. We combine BLS data with independent measurements of cellular and nuclear volumes obtained via fluorescence exclusion microscopy, as well as with nanoparticle diffusion assays. This multimodal approach enables a comparison between acoustic parameters and physical properties such as viscosity and macroscopic density. We interpret the data using two theoretical frameworks from soft matter physics: mixing laws and poroelasticity theory, the latter describing interactions between a solid matrix and an interstitial fluid. Our results show that neither mixing laws alone nor purely mechanical interpretations are sufficient to explain the measured signals. In contrast, the joint analysis of Brillouin shift and linewidth, interpreted within a poroelastic framework, provides a more coherent understanding of the acoustic properties of cells. This thesis thus contributes to repositioning Brillouin microscopy as a quantitative and physically grounded acoustic tool for the study of living biological materials, incorporating a critical reflection on its mechanical interpretation. This work highlights the importance of poroelastic dissipation, which appears to be intimately linked to nuclear structure. ''