Description:

 Eva Zhao, PhD Student, Motter Group

"Hysteresis and Nongenetic Traits in Bacterial Regulatory Networks"

A fundamental biophysical question is how bacteria may exhibit non-genetic phenotypic differences that are heritable in the absence of epigenetic modifications. Here, we address this question by modeling and recognizing the reconstructed regulatory network of E. coli as a multistable Boolean network system. In this model, different gene expression profiles (which may underlie different phenotypes) correspond to distinct stable states, and we show that persistent transitions between expression profiles can be induced by transient genetic perturbations. These persistent transitions are expected to become hysteretic under stochastically fluctuating conditions. Comparison with experiments indicates that genes exhibiting persistent transcriptional changes in our model tend to show compensatory transcriptional changes in adaptive evolution responses.

Leone Luzzatto, PhD Student, Kovacs Group

"Probing the Geometry of Critical Systems through Cluster Tomography"

Critical points are characterized by complex spatial correlation that span the entirety of a physical system, a consequence of a diverging correlation length. The lack of a typical length-scale in critical systems has striking effects on the properties of its geometric domains – or clusters – which exhibit a broad distribution of sizes and are separated by infinitely rough, fractal-like boundaries. In this talk, I will describe a novel methodology for the study of critical systems based on previously little explored geometric properties of their clusters. Our methodology, which we call cluster tomography, consists of two key steps: (i) identify an appropriate definition of geometric clusters in a system and (ii) study one dimensional cross-sections of the clustered system. Cluster tomography has proven to be a powerful and versatile tool, capable of providing insight into the critical behavior of a variety of systems both in- and out-of-equilibrium.