Monday, December 18th, 11h30, Room 454 A, Condorcet Building.

Two back-to-back presentations of 30 minutes each by two members of MSC. Xiuyu Wang (Physique du Vivant) and Emilien Dilly (DOMM).

Xiuyu Wang

Mechanical properties of the cell nucleus and cancer aggressiveness

Abstract :
A- and B-type lamins form the nuclear lamina, which impacts the nuclear mechanical properties, chromatin organization, and gene expression. Lamin A/C is responsible for viscosity and stiffness of the nuclear envelope, while Lamin B confers elasticity. In the last decades, the role of lamins in mechanosignaling has been widely discussed. Using Glioblastoma Multiforme (GBM) as a model, we found that Lamin A is a potential candidate as a marker for GBM aggressiveness.
We have investigated nuclear shape and rheology, together with cell proliferation and migration in GBM patient-derived cells. We found that aggressiveness-associated elements can be correlated with the lamin expression levels. In contrast with other cancer types, a stiffer nucleus facilitates the migration and invasion of GBM cells in the softest tissue of the human body, the brain. We show that a combination of whole cell and intracellular rheology approaches may effectively differentiate the mechanical characteristics of GBM cells of various aggressiveness. Our study shows that Lamin A levels positively correlate with the nucleus area, its elasticity, GBM cell proliferation rate and migration and negatively correlate with patient survival time.

Emilien Dilly

Biomechanics of Tendril Writhing: How to Pull When Growth is Your Only Option?

Abstract:
Certain climbing plants employ specialized structures known as tendrils (found in cucumbers, vines, passion fruit, etc.) to anchor themselves to supports and ascend. Initially, a tendril explores its surroundings, locates a support, and wraps itself around it. As the tendril continues to curve, it establishes a spring-like connection between the support and the plant (see image). Through differential growth, inducing curvature generation, this spring connection tightens, resulting in a pulling force that draws the plant closer to its support. This phenomenon involves the notion of mechanosensitivity—does the presence of a pulling force impact the plant’s ability to curve? How are these factors interconnected?
    We conducted experiments to study the dynamics of tendril writhing under mechanical constraints. By maintaining a fixed tension force in the tendril, we investigated the repercussions of such constraints on curvature generation. Our results indicate that tendril writhing can be effectively described with a bilayer model, where one layer undergoes growth. Additionally, the influence of mechanosensitivity can be aptly described by a linearly slowed growth in response to stress, leading to a critical tension beyond which writhing does not occur, as observed in our experiments.
During the seminar, I will first present experiments conducted on elastomer-based systems that illustrate the writhing instability, resulting in the characteristic features of helices with opposite chiralities. Then, I will show that, with differential growth, the tendril can undergo the writhing instability and form the spring-like connection. Finally, I will discuss experiments involving tendril writhing under loads, along with the modeling of mechanosensitivity and the intricate relationship between growth and tissue stress.

À lire aussi