Biology subjects

Fleck, C.

Publications and source records attributed to Fleck, C..

4 recordsLinked to original sources

bioRxiv2023

Spectral methods for prediction uncertainty quantification in Systems Biology

Uncertainty is ubiquitous in biological systems. These uncertainties can be the result of lack of knowledge or due to a lack of appropriate data. Additionally, the natural variability of biological systems caused by intrinsic noise, e.g. in stochastic gene expression, leads to uncertainties. With the help of numerical simulations the impact of these uncertainties on the model predictions can be assessed, i.e. the impact of the propagation of uncertainty in model parameters on the model response can be quantified. Taking this into account is crucial when the models are used for experimental design, optimisation, or decision-making, as model uncertainty can have a significant effect on the accuracy of model predictions. We focus here on spectral methods to quantify prediction uncertainty based on a probabilistic framework. Such methods have a basis in, e.g., computational mathematics, engineering, physics, and fluid dynamics, and, to a lesser extent, systems biology. In this chapter, we highlight the advantages these methods can have for modelling purposes in systems biology and do so by providing a novel and intuitive scheme. By applying the scheme to an array of examples we show its power, especially in challenging situations where slow converge due to high-dimensionality, bifurcations, and spatial discontinuities play a role.

systems biology↗

bioRxiv2021

Single Cell Variability of CRISPR-Cas Interference and Adaptation

CRISPR-Cas defence is a combination of adaptation to new invaders by spacer acquisition, and interference by targeted nuclease activity. While these processes have been studied on a population level, the individual cellular variability has remained unknown. Here, using a microfluidic device combined with time-lapse microscopy, we monitor invader clearance in a population of Escherichia coli across multiple generations. We observed that CRISPR interference is fast with a narrow distribution of clearance times. In contrast, for invaders with escaping PAM mutations we show large cell-to-cell variability of clearance times, which originates from primed CRISPR adaptation. Faster growth and cell division, as well as higher levels of Cascade, increase the chance of clearance by interference. In contrast, faster growth is associated with decreased chances of clearance by priming. A mathematical model explains the experimental findings, and identifies Cascade binding to the mutated invader DNA, rather than spacer integration, as the main source of priming heterogeneity. The highly stochastic nature of primed CRISPR adaptation implies that only subpopulations of bacteria are able to respond to invading threats in a timely manner. We conjecture that CRISPR-Cas dynamics and heterogeneity at the cellular level are crucial to understanding the strategy of bacteria in their competition with other species and phages.

microbiology↗

bioRxiv2018

Live cell imaging of meiosis in Arabidopsis thaliana - a landmark system

Meiosis is essential for sexual reproduction and key to the generation of genetic diversity. To reveal the robustness of meiocyte differentiation and progression through meiosis, we have here established a live cell imaging setup to follow the dynamics of individual male meiocytes in Arabidopsis. Our method is based on the concomitant visualization of microtubules and a meiotic cohesion subunit that allowed following five cellular parameters: cell shape, nucleus position, nucleolus position, chromatin condensation and microtubule array. We find that the states of these parameters are not randomly associated and identify 11 states, referred to as landmarks, that occur much more frequently than closely related states, indicating that they are convergent points of meiotic progression. With this, the here-presented landmark system represents a novel method to analyze meiosis not only allowing a high-temporal dissection but also providing new criteria to evaluate mutants or environmental effects on meiosis.

cell biology↗

bioRxiv2018

Optogenetic control shows that kinetic proofreading regulates the activity of the T cell receptor

The pivotal task of the immune system is to distinguish between self and foreign antigens. The kinetic proofreading model (KPR) proposes that T cells discriminate self from foreign ligands by the different ligand binding half-lives to the T cell receptor (TCR). It is challenging to test KPR as the available experimental systems fall short of only altering the binding half-lives and keeping other parameters of the ligand-TCR interaction unchanged. We engineered an optogenetic system using the plant photoreceptor phytochrome B to selectively control the dynamics of ligand binding to the TCR by light. Combining experiments with mathematical modeling we find that the ligand-TCR interaction half-life is the decisive factor for activating downstream TCR signaling, substantiating the KPR hypothesis.\n\nOne Sentence SummaryThe half-life of the ligand-T cell receptor complex determines T cell activation.

immunology↗