Bacterial cells constantly face complex environmental changes in their natural habitats. While steady-state cell size correlates with nutrient-determined growth rate, it remains unclear how cells regulate their morphology during rapid environmental changes. Here, we systematically quantified cellular dimensions throughout passage cycles of stationary-phase cells diluted into fresh medium and grown back to saturation, and found that cells exhibit characteristic dynamics in surface area to volume ratio (SA/V). SA/V dynamics were conserved across many genetic/chemical perturbations, as well as across species and growth temperatures. We developed a model with a single fitting parameter, the time delay between surface and volume synthesis, that quantitatively explained our SA/V observations, and showed that the time delay was indeed due to differential expression of volume and surface-related genes. The first division after dilution occurred at a tightly controlled SA/V, a previously unrecognized size-control mechanism highlighting the relevance of SA/V. Finally, our time-delay model successfully predicted the quantitative changes in SA/V dynamics due to altered surface area synthesis rates or time delays from translation inhibition. Our minimal model thus provides insight into how cells regulate their morphologies through differential regulation of surface area and volume synthesis and potentiates deep understanding of the connections between growth rate and cell shape in complex environments.

/pdf/precise-regulation-of-the-relative-rates-of-surface-area-and-48brnvxhvx.pdf

Precise regulation of the relative rates of surface area and volume synthesis in dynamic environments

The neuronal basis of goal-directed behavior requires interaction of multiple separated brain regions. How subcortical regions and their interactions with brain-wide activity are involved in action selection is less understood. We have investigated this question by developing an assay based on whole-brain volumetric calcium imaging using light-field microscopy combined with an operant-conditioning task in larval zebrafish. We find global and recurring dynamics of brain states to exhibit pre-motor bifurcations towards mutually exclusive decision outcomes which arises from a spatially distributed network. Within this network the cerebellum shows a particularly strong pre-motor activity, predictive of both the timing and outcome of behavior up to ~10 seconds before movement initiation. Furthermore, on the single-trial level, decision directions can be inferred from the difference neuroactivity between the ipsilateral and contralateral hemispheres, while the decision time can be quantitatively predicted by the rate of bi-hemispheric population ramping activity. Our results point towards a cognitive role of the cerebellum and its importance in motor planning.

/pdf/cerebellar-neurodynamics-during-motor-planning-predict-3sv4k4fhe9.pdf

Cerebellar neurodynamics during motor planning predict decision timing and outcome on single-trial level

The focused ion beam (FIB) is a relatively novel technique to biomedical electron microscopy as it open up new means for the observations and examinations of a wide range of biomedical and biological materials. The focused ion beam, or FIB tool has been utilized mainly in the fields of material sciences and industry. The (FIB) uses high-energy gallium ions to precisely and accurately section or mill samples. Lately FIB method have been used to prepare biological samples such as yeast cells and virus particles. Yeast cells Schwanniomyces occidentalis S. occidentalis were prepared by vacuum sucking them into cellulose tubing, plunge freezing them in liquid nitrogen, followed by chemical fixation in glutaraldehye and postfixed with osmium tetroxide, dehydrated in a series of ascending alcohol concentration up to absolute alcohol, then freeze dried overnight. In the case of SARS virus, the tissue culture containing virus particles was chemically fixed with glutaraldehyde, dehydrated in ascending order of alcohol concentrations and then freeze dried.

/pdf/applications-of-focused-ion-beam-fib-on-yeast-cell-sars-2bqrzk4wca.pdf

Applications of Focused Ion Beam (FIB) on Yeast Cell & SARS Virus

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Applications of Focused Ion Beam (FIB) on Yeast Cell & SARS Virus