# 2012

7th Lorenz Kramer Memorial Lecture:

## Can Physics Describe Cell and Tissue Dynamics?

**Prof. Dr. Jacques Prost**

(ESPCI & Curie Institute, Paris, France)

October 5, 2012

Abstract:

Much of the cell mechanics, morphology and motility is determined by the dynamical properties of an actin network moving under the action of molecular motors and by a continuous process of polymerization/depolymerization called treadmilling. The actin network constitutes a physical gel the cross-links of which are both temporary and mobile. It is more complex than a physical gel in that it has a macroscopic polarity due to the microscopic polarity of actin filaments and in that the cross-links are dynamically redistributed by molecular motors. I will show how one can write down a set of phenomenological equations, which can describe this situation. I will illustrate the usefulness of this approach by considering a few examples concerning cell dynamics such as cell wound healing and cell division.

In the second part of the lectures, I will show how a simple extension of this theory allows us to discuss salient features of tissue dynamics. After introducing the notion of homeostatic pressure, I will first show that when two tissues compete for space, in the absence of chemical signaling, the one, which has the largest homeostatic pressure, always win. I will then show that in order for a micro-tumor to grow it must exceed a critical radius and calculate the probability for a tumor to exceed that radius. I will subsequently introduce dynamical equations, which exhibit fluid like behavior on time scales long compared to duplication and apoptosis times, in the vicinity of homeostatic conditions and show how our theory can reproduce all structures observed in intestinal villi. At last, I will also describe stress-clamp experiments, which provide numbers on the effects of stress on cell division and apoptosis.