Biology subjects

Clark-Cotton, M. R.

Publications and source records attributed to Clark-Cotton, M. R..

3 recordsLinked to original sources

bioRxiv2024

Imaging-based screen identifies novel natural compounds that perturb cell and chloroplast division in Chlamydomonas reinhardtii

Successful cell division requires faithful division and segregation of organelles into daughter cells. The unicellular alga Chlamydomonas reinhardtii has a single, large chloroplast whose division is spatiotemporally coordinated with furrowing. Cytoskeletal structures form in the same plane at the midzone of the dividing chloroplast (FtsZ) and the cell (microtubules), but how these structures are coordinated is not understood. Previous work showed that loss of F-actin blocks chloroplast division but not furrow ingression, suggesting that pharmacological perturbations can disorganize these events. In this study, we developed an imaging platform to screen natural compounds that perturb cell division while monitoring FtsZ and microtubules and identified 70 unique compounds. One compound, curcumin, has been proposed to bind to both FtsZ and tubulin proteins in bacteria and eukaryotes, respectively. In C. reinhardtii, where both targets coexist and are involved in cell division, curcumin at a specific dose range caused a severe disruption of the FtsZ ring in chloroplast while leaving the furrow-associated microtubule structures largely intact. Time-lapse imaging showed that loss of FtsZ and chloroplast division failure delayed the completion of furrowing but not the initiation, suggesting that the chloroplast-division checkpoint proposed in other algae requires FtsZ or is absent altogether in C. reinhardtii. SIGNIFICANCE STATEMENTO_LISuccessful cell division requires the coordination of both organelle inheritance and cytokinesis. The unicellular alga Chlamydomonas reinhardtii, which spatiotemporally coordinates the division of its chloroplast with cytokinesis, is an excellent model to study the regulation. C_LIO_LIWe screened libraries of natural compounds for perturbations of cell and/or chloroplast division, identifying 70 unique chemicals. By time-lapse microscopy using one of the hits, curcumin, we demonstrate that although chloroplast division failures delay the completion of cytokinesis, it does not impair initiation. C_LIO_LIThese findings suggest that the chloroplast-division checkpoint proposed in other algae requires FtsZ or is absent altogether in C. reinhardtii. C_LI

cell biology↗

bioRxiv2020

Exploratory polarization facilitates mating partner selection in Saccharomyces cerevisiae

Yeast decode pheromone gradients to locate mating partners, providing a model for chemotropism. How yeast polarize toward a single partner in crowded environments is unclear. Initially, cells often polarize in unproductive directions, but then they relocate the polarity site until two partners polarity sites align, whereupon the cells "commit" to each other by stabilizing polarity to promote fusion. Here we address the role of the early mobile polarity sites. We found that commitment by either partner failed if just one partner was defective in generating, orienting, or stabilizing its mobile polarity sites. Mobile polarity sites were enriched for pheromone receptors and G proteins, and we suggest that such sites engage in an exploratory search of the local pheromone landscape, stabilizing only when they detect elevated pheromone levels. Mobile polarity sites were also enriched for pheromone secretion factors, and simulations suggest that only focal secretion at polarity sites would produce high pheromone concentrations at the partners polarity site, triggering commitment.

cell biology↗

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↗