Biology subjects

Graf, I.

Publications and source records attributed to Graf, I..

4 recordsLinked to original sources

bioRxiv2026

Assembly-coupled feedback enables robust control of flagellar number

Bacteria assemble a precise number of flagella to navigate their environment, yet the molecular mechanisms underlying this robust counting remain poorly understood. We propose that robust flagellar number control does not require a strictly conserved transcriptional gene hierarchy, but instead emerges from a conserved network motif in which transcriptional feedback is coupled to the assembly progress of the flagellar C-ring. Specifically, upon C-ring growth, the ATPase FlhG is released from a non-inhibitory FlhG-FliM complex, dimerizes, and inactivates the master regulator FlrA, shutting down early flagellar gene expression. We analyze this assembly-coupled feedback mechanism using stochastic simulations and analytical calculations, revealing a trade-off between robustness to intrinsic fluctuations and to cell-to-cell variability in regulator abundance. Only at the crossover between fast and slow inactivation regimes can robustness to both noise sources be achieved simultaneously. These results provide quantitative, organism-independent insight into flagellar number control and connect to the broader problem of stochastic regulation of absorbing-state statistics.

biophysics↗

bioRxiv2025

High-Purity Enrichment of Extracellular Vesicles from Diverse Sources by Conventional and Image-Based Fluorescence Activated Cell Sorters for Robust Downstream Applications

Selective enrichment of extracellular vesicle (EV) subpopulations from the heterogeneous EV pool is essential for understanding their characteristic biological functions and exploiting their potential as diagnostic and prognostic biomarkers. However, isolation of specific EV-subsets remains challenging. Fluorescence-Activated Cell Sorting (FACS) has emerged as promising technique for EV subpopulations enrichment, despite limitations associated to their small size. Although FACS-based EV sorting has been reported, a broadly applicable and systematically validated workflow is still lacking. Here, we describe and validate an optimized workflow for the sorting and analysis of EVs derived from diverse species, tissues, blood and cell culture systems. Using two advanced flow cytometric cell sorters, the BD FACSAria Fusion, and the BD FACSDiscover S8, we systematically evaluated key technical parameters, including nozzle size, sample dilutions, and sorting mode. The optimized workflow enabled efficient enrichment of differently labelled EV populations of interest, achieving near-100% purity, including rare subsets representing less than 10% of the total EV pool, while maintaining compatibility with downstream analyses. Sorted EV populations were characterized by high-sensitivity imaging flow cytometry, transmission electron microscopy, and liquid chromatography-tandem mass spectrometry. This workflow provides a robust framework for EV subset isolation and characterization, supporting both fundamental EV research and translational biomarker applications.

cell biology↗

bioRxiv2022

Effects of dopamine D2 and opioid receptor antagonism on the trade-off between model-based and model-free behavior in healthy volunteers

Our daily behaviour requires a flexible arbitration between actions we do out of habit and actions that are directed towards a specific goal. Drugs that target opioid and dopamine receptors are notorious for inducing maladaptive habitual drug consumption, yet how the opioidergic and dopaminergic neurotransmitter systems contribute to the arbitration between habitual and goal-directed behaviour is poorly understood. By combining pharmacological challenges with a well-established decision-making task and a novel computational model, we show that the administration of the D2 dopamine receptor antagonist amisulpride led to an increase in goal-directed or model-based relative to habitual or model-free behaviour, whereas the non-selective opioid receptor antagonist naltrexone had no appreciable effect. These findings highlight the distinct functional contributions of dopamine and opioid receptors to goal-directed and habitual behaviour and support the notion that D2 receptor antagonists promote stabilisation of goal-relevant information.

neuroscience↗

bioRxiv2019

Dopaminergic and opioidergic regulation of implicit and explicit wanting and liking of social and nonsocial rewards

The observation of animal hedonic orofacial and behavioral reactions has played a fundamental role for the identification of a dopaminergic motivational, and an opioidergic hedonic component of reward. Translation to humans remains difficult, however, as human research has struggled to adopt a similar operationalization of reward. Here, we investigated the neurochemical basis of hedonic facial and behavioral reactions to different types of rewards in healthy adult volunteers, by pharmacologically reducing dopaminergic and opiodergic receptor-specific action. Subjective ratings, physical effort, and facial reactions to matched primary social (affective touch) and nonsocial (food) rewards were assessed. Both drugs resulted in reduced physical effort and increased negative facial reactions during reward anticipation, but only opioidergic manipulation caused reduced positive facial reactions during reward consumption. This suggest that facial reactions during anticipated and experienced pleasure rely on partly different neurochemical systems, providing novel evidence in support of existing theoretical models of reward.

neuroscience↗