Tsevi Beatus

Various p53 mutant proteins differently regulate the Ras circuit to induce a cancer-related gene signature

Summary Concomitant expression of mutant p53 and oncogenic Ras, leading to cellular transformation, is well documented. However, the mechanisms by which the various mutant p53 categories cooperate with Ras remain largely obscure. From this study we suggest that different mutant p53 categories cooperate with H-Ras in different ways to induce a unique expression pattern of a cancer-related gene signature (CGS). The DNA-contact p53 mutants (p53R248Q and p53R273H) exhibited the highest level of CGS expression by cooperating with NF&kgr;B. Furthermore, the Zn+2 region conformational p53 mutants (p53R175H and p53H179R) induced the CGS by elevating H-Ras activity. This elevation in H-Ras activity stemmed from a perturbed function of the p53 transcription target gene, BTG2. By contrast, the L3 loop region conformational mutant (p53G245S) did not affect CGS expression. Our findings were further corroborated in human tumor-derived cell lines expressing Ras and the aforementioned mutated p53 proteins. These data might assist in future tailor-made therapy targeting the mutant p53–Ras axis in cancer.

Damped oscillations in the adaptive response of the iron homeostasis network of E. coli

Living organisms often have to adapt to sudden environmental changes and reach homeostasis. To achieve adaptation, cells deploy motifs such as feedback in their genetic networks, endowing the cellular response with desirable properties. We studied the iron homeostasis network of E. coli, which employs feedback loops to regulate iron usage and uptake, while maintaining intracellular iron at non‐toxic levels. Using fluorescence reporters for iron‐dependent promoters in bulk and microfluidics‐based, single‐cell experiments, we show that E. coli cells exhibit damped oscillations in gene expression, following sudden reductions in external iron levels. The oscillations, lasting for several generations, are independent of position along the cell cycle. Experiments with mutants in network components demonstrate the involvement of iron uptake in the oscillations. Our findings suggest that the response is driven by intracellular iron oscillations large enough to induce nearly full network activation/deactivation. We propose a mathematical model based on a negative feedback loop closed by rapid iron uptake, and including iron usage and storage, which captures the main features of the observed behaviour. Taken together, our results shed light on the control of iron metabolism in bacteria and suggest that the oscillations represent a compromise between the requirements of stability and speed of response.

An autonomous system for identifying and governing a cell's state in yeast

We present an approach for an autonomous system that detects a particular state of interest in a living cell and can govern cell fate accordingly. Cell states could be better identified by the expression pattern of several genes than of a single one. Therefore, autonomous identification can be achieved by a system that measures the expression of these several genes and integrates their activities into a single output. We have constructed a system that diagnoses a unique state in yeast, in which two independent pathways, methionine anabolism and galactose catabolism, are active. Our design is based on modifications of the yeast two-hybrid system. We show that cells could autonomously report on their state, identify the state of interest, and inhibit their growth accordingly. The systems sensitivity is adjustable to detect states with limited dynamic range of inputs. The systems output depends only on the activity of input pathways, not on their identity; hence it is straightforward to diagnose any pair of inputs. A simple model is presented that accounts for the data and provides predictive power. We propose that such systems could handle real-life states-of-interest such as identification of aberrant versus normal growth.

One-Dimensional Microfluidic Crystals Far from Equilibrium Acoustic Phonons, Instabilities and Confinement

We investigated the collective motion of a one-dimensional array of water-in-oil droplets flowing in microfluidic channel in quasi-2D at low Reynolds number. Driven far from equilibrium by the symmetry-breaking flow field, the droplets exhibit acoustic normal modes (crystal ‘phonons’) with unusual dispersion relations. These phonons are due to long-range hydrodynamic dipolar interactions between the droplets. The phonon spectra change anomalously at the crossover between unconfined 2D flow and 1D confined flow, as a result from an interplay between boundary-induced screening and crystal incompressibility. Microfluidic crystals offer a vista, in the linear flow regime, into soft-matter systems far from equilibrium.