Biology subjects

Lew, D. J.

Publications and source records attributed to Lew, D. J..

3 recordsLinked to original sources

bioRxiv2018

How yeast cells find their mates

Accurate detection of extracellular chemical gradients is essential for many cellular behaviors. Gradient sensing is challenging for small cells, which experience little difference in ligand concentrations on the up-gradient and down-gradient sides of the cell. Nevertheless, the tiny cells of the yeast Saccharomyces cerevisiae reliably decode gradients of extracellular pheromones to find their mates. By imaging the behavior of polarity factors and pheromone receptors during mating encounters, we found that gradient decoding involves two steps. First, cells bias orientation of initial polarity up-gradient, even though they have unevenly distributed receptors. To achieve this, they measure the local fraction of occupied receptors, rather than absolute number. However, this process is error-prone, and subsequent exploratory behavior of the polarity factors corrects initial errors via communication between mating partners. The mobile polarity sites convert the difficult problem of spatial gradient decoding into the easier one of sensing temporal changes in local pheromone levels.

cell biology↗

bioRxiv2018

Mating in wild yeast: variable interest in sex after spore germination

Studies of lab strains of Saccharomyces cerevisiae have uncovered signaling pathways involved in mating, including information processing strategies to optimize decisions to mate or to bud. However, lab strains are heterothallic (unable to self-mate) while wild yeast are homothallic. And while mating of lab strains is studied using cycling haploid cells, mating of wild yeast is thought to involve germinating spores. Thus, it was unclear whether lab strategies would be appropriate in the wild. Here, we have investigated the behaviors of several yeast strains derived from wild isolates. Following germination, these strains displayed large differences in their propensity to mate or to enter the cell cycle. The variable interest in sex following germination was correlated with differences in pheromone production, which were due to both cis- and trans-acting factors. Our findings suggest that yeast spores germinating in the wild may often enter the cell cycle and form microcolonies prior to engaging in mating.

cell biology↗

bioRxiv2017

Principles that govern competition or co-existence in Rho-GTPase driven polarization

Rho-GTPases are master regulators of polarity establishment and cell morphology. Positive feedback enables concentration of Rho-GTPases into clusters at the cell cortex, from where they regulate the cytoskeleton. Different cell types reproducibly generate either one (e.g. the front of a migrating cell) or several clusters (e.g. the multiple dendrites of a neuron), but the mechanistic basis for uni-polar or multi-polar outcomes is unclear. The design principles of Rho-GTPase circuits are captured by reaction-diffusion models based on conserved aspects of Rho-GTPase biochemistry. Some such models display rapid winner-takes-all competition between clusters, yielding a unipolar outcome. Other models allow prolonged co-existence of clusters. We derive a \"saturation rule\" general to all relevant models that governs the timescale of competition, and thereby predicts whether the system will generate uni-polar or multi-polar outcomes. We suggest that the saturation rule is a fundamental property of the Rho-GTPase polarity machinery, regardless of the specific feedback mechanism.

cell biology↗