Biology subjects

Amselem, G.

Publications and source records attributed to Amselem, G..

3 recordsLinked to original sources

bioRxiv2023

Measuring single-cell susceptibility to antibiotics within monoclonal bacterial populations

Given the emergence of antimicrobial drug resistance, it is critical to understand the heterogeneity of response to an antibiotic within a population of cells. Since the drug can exert a selection pressure that leads to the emergence of resistant phenotypes. To date, neither bulk nor single-cell methods are able to link the heterogeneity of single-cell susceptibility to the population-scale response to antibiotics. Here we present a platform that measures the ability of individual E. coli cells to form small colonies at different ciprofloxacin concentrations, by using anchored microfluidic drops and an image and data analysis pipelines. The microfluidic results are benchmarked against classical microbiology measurements of antibiotic susceptibility, showing an agreement between the pooled microfluidic chip and replated bulk measurements. Further, the experimental likelihood of a single cell to form a colony is used to provide a probabilistic antibiotic susceptibility curve. In addition to the probabilistic viewpoint, the microfluidic format enables the characterization of morphological features over time for a large number of individual cells. This pipeline can be used to compare the response of different bacterial strains to antibiotics with different action mechanisms.

bioengineering↗

bioRxiv2020

High-throughput measurements of intra-cellular and secreted cytokine from single spheroids using anchored microfluidic droplets

While many single-cell approaches have been developed to measure secretion from anchorage-independent cells, these protocols cannot be applied to adherent cells, especially when these cells requires to be cultured in 3D formats. Here we demonstrate a platform to measure the secretions from individual spheroids of human mesenchymal stem cells, cultured within microfluidic droplets. The platform allows us to quantify the secretion from hundreds of individual spheroids in each device, by using a secondary droplet to bring functionalized micro-beads into proximity with each spheroid. We focus on vascular endothelial growth factor (VEGF) and measure a distribution of secretion levels that presents broad heterogeneity within the population of spheroids. Moreover, the intra-cellular level of VEGF-A on each spheroid, measured through immuno-staining, correlates well with the extra-cellular measurement, indicating that the heterogeneities observed at the spheroids level result from variations at the scale of individual cells. Finally, we model the molecular accumulation within the droplets and find that physical confinement is crucial for measurements of protein secretions. The model predicts the time to achieve a measurement, which scales with droplet volume. Therefore these first measurements of secretions from individual spheroids provide several new biological insights.

bioengineering↗

bioRxiv2019

Mapping Structure and Biological Functions within Mesenchymal Bodies using Microfluidics

Organoids that recapitulate the functional hallmarks of anatomic structures comprise cell populations able to self-organize cohesively in 3D. However, the rules underlying organoid formation in vitro remain poorly understood because a correlative analysis of individual cell fate and spatial organization has been challenging. Here, we use a novel microfluidics platform to investigate the mechanisms determining the formation of organoids by human mesenchymal stromal cells that recapitulate the early steps of condensation initiating bone repair in vivo. We find that heterogeneous mesenchymal stromal cells self-organize in 3D in a developmentally hierarchical manner. We demonstrate a link between structural organization and local regulation of specific molecular signaling pathways such as NF-{kappa}B and actin polymerization, which modulate osteo-endocrine functions. This study emphasizes the importance of resolving spatial heterogeneities within cellular aggregates to link organization and functional properties, enabling a better understanding of the mechanisms controlling organoid formation, relevant to organogenesis and tissue repair.

cell biology↗