Biology subjects

Rieu, J.-P.

Publications and source records attributed to Rieu, J.-P..

6 recordsLinked to original sources

bioRxiv2026

Mechanical analysis of spatiotemporal traction stress dynamics in a bleb-driven migrating cell, Amoeba proteus

Many adherent eukaryotic cells exhibit amoeboid locomotion, where traction stress exerted on the substrate is essential for movement. In this study, we investigated the spatiotemporal development of these forces in Amoeba proteus to clarify the mechanical dynamics underlying bleb-driven migration. By performing a multipole analysis of the stress distribution, we characterized the spatiotemporal patterns exhibited by motile cells. Furthermore, we tracked the behavior of individual localized peak structures within these profiles, which are thought to correspond to focal contact sites. These analyses revealed that the front-back asymmetry in the traction distribution correlates with the direction of migration. We also found that A. proteus exhibits a periodic pattern in which inward-directed stresses are alternately strengthened and weakened at the cell poles. Crucially, we identified a distinctive feature not observed in other cell types: the generation of large lateral traction forces at the cell center. Together, these results highlight both the universality and diversity of the biophysical mechanisms driving amoeboid locomotion.

biophysics↗

bioRxiv2025

Dictyostelium discoideum chemotaxis is altered by hypoxia to orient streaming toward higher oxygen level independently of aerotaxis.

BackgroundDictyostelium discoideum (Dd) exhibits a unique life cycle marked by its transition from single-cell amoeboid movement to multicellular development in response to environmental stimuli. While its chemotactic response to cyclic adenosine monophosphate (cAMP) has been extensively studied, experiments are usually carried out in a high oxygen environment (21% O2, also called normoxia) that might not reflect the natural condition for a soil amoeba as hypoxia is common underground. Our recent research has unveiled a novel phenomenon termed aerotaxis, wherein Dd cells migrate towards oxygen-rich environments under low oxygen (hypoxia). ResultsWe tested Dd response when submitted to two different stress sources: starvation and hypoxia. While both stresses induce a motile response, namely chemotaxis and aerotaxis, we were able to decoupled both type of responses to explore potential shared mechanisms. Importantly, aerotaxis appears to be operated independently of known chemotactic pathways, demonstrating unique signaling pathways and cellular responses. Aerotaxis contributes to Dd developmental processes by letting cells escape from acute hypoxia. Even though chemotactic response can occur at less than 2% O2, it does not lead to well organized or stable streaming. Furthermore, in an oxygen gradient, aggregation center for chemotactic response appears preferentially at higher O2 level. RT-qPCR analysis show that hypoxia only slightly reduces the expression of genes required for chemotactic response, suggesting that the bias toward high O2 might occur at another level. Reoxygenation of cells that have been starved in hypoxic condition for 18h allow rapid aggregation but require de novo protein synthesis. ConclusionAerotaxis and chemotaxis mechanisms do not interact directly. However, when cells are exposed to both hypoxia and starvation, both mechanisms can be combined to direct the migration of cells toward place with higher oxygen level. As hypoxia is frequent in the soil where Dd usually grow, formation of aggregation centers at, or close to the soil surface, where oxygen is abundant, will be advantageous. Low O2 level does not preclude cells to participate to streaming but seems to reduce or delay their ability to produce stable aggregation centers, resulting into bias favoring centers that form at higher oxygen level.

cell biology↗

bioRxiv2025

Global characterization of Dictyostelium discoideum gene expression changes under hypoxic conditions

Aerobic eukaryotes utilize O2 to oxidize metabolites and generate ATP. The protist kingdom lacks the Hypoxia Inducible Factor-dependent transcriptional response network to accommodate low O2 though possesses a HIF prolyl hydroxylase that initially mediates the response. To address the scale and scope of hypoxic responses in protists, we characterized transcriptomic and proteomic changes when the social amoeba Dictyostelium is subjected to low (1%) O2 under nutritive conditions over 24 h followed by reoxygenation. Remarkably, 32% of the transcripts quantified were differentially expressed during hypoxia, with greatest changes associated with early (1 h) and late phases (24 h). Protein changes were modestly correlated with and generally lagged behind transcriptional changes. Correlated changes were observed for transcripts and proteins associated with various metabolic, anabolic, and catabolic pathways, as well as chromosome organization, cell cycling, vesicular trafficking, and signaling. Analysis of 4 marker genes showed extremely rapid responses that were graded over a range of O2 levels, with differential responses to inhibitors affecting protein synthesis and mitochondria. Overall, the amoebal response to a low but non-toxic O2-level resulted in massive remodeling of the transcriptome and proteome.

genomics↗

bioRxiv2022

Microphase separation of living cells

Self-organization of cells is central to a variety of biological systems and physical concepts of condensed matter have proven instrumental in deciphering some of their properties. Here we show that microphase separation, long studied in polymeric materials and other inert systems, has a natural counterpart in living cells. When placed below a millimetric film of liquid nutritive medium, a quasi two-dimensional, high-density population of Dictyostelium discoideum cells spontaneously assemble into compact domains. Their typical size of 100 m is governed by a balance between competing interactions: an adhesion acting as a short-range attraction and promoting aggregation, and an effective long-range repulsion stemming from aerotaxis in near anoxic condition. Experimental data, a simple model and cell-based simulations all support this scenario. Our findings establish a generic mechanism for self-organization of living cells and highlight oxygen regulation as an emergent organizing principle for biological matter.

biophysics↗

bioRxiv2020

Hypoxia triggers collective aerotactic migration in Dictyostelium discoideum

It is well known that eukaryotic cells can sense oxygen (O2) and adapt their metabolism accordingly. It is less known that they can also move towards regions of higher oxygen level (aerotaxis). Using a self-generated hypoxic assay, we show that the social amoeba Dictyostelium discoideum displays a spectacular aerotactic behavior. When a cell colony is covered by a coverglass, cells quickly consume the available O2 and the ones close to the periphery move directionally outward forming a dense ring keeping a constant speed and density. To confirm that O2 is the main molecular player in this seemingly collective process, we combined two technological developments, porphyrin based O2 sensing films and microfluidic O2 gradient generators. We showed that Dictyostelium cells exhibit aerotactic and aerokinetic (increased speed at low O2) response in an extremely low range of O2 concentration (0-1.5%) indicative of a very efficient detection mechanism. The various cell behaviors under self-generated or imposed O2 gradients were modeled with a very satisfactory quantitative agreement using an in silico cellular Potts model built on experimental observations. This computational model was complemented with a parsimonious Go or Grow partial differential equation (PDE) model. In both models, we found that the collective migration of a dense ring can be explained by the interplay between cell division and the modulation of aerotaxis, without the need for cell-cell communication.

biophysics↗

bioRxiv2020

Development of a soft cell confiner to decipher the impact of mechanical stimuli on cells

Emerging evidence suggests the importance of mechanical stimuli in normal and pathological situations for the control of many critical cellular functions. While the effect of matrix stiffness has been and is still extensively studied, few studies have focused on the role of mechanical stresses. The main limitation of such analyses is the lack of standard in vitro assays enabling extended mechanical stimulation compatible with dynamic biological and biophysical cell characterization. We have developed an agarose-based microsystem, the soft cell confiner, which enables the precise control of confinement for single or mixed cell populations. The rigidity of the confiner matches physiological conditions and enables passive medium renewal. It is compatible with time-lapse microscopy, in situ immunostaining, and standard molecular analyses, and can be used with both adherent and non-adherent cell lines. Cell proliferation of various cell lines (hematopoietic cells, MCF10A epithelial breast cells and HS27A stromal cells) was followed for several days up to confluence using video-microscopy and further documented by Western blot and immunostaining. Interestingly, even though the nuclear projected area was much larger upon confinement, with many highly deformed nuclei (non-circular shape), cell viability, assessed by live and dead cell staining, was unaffected for up to 8 days in the confiner. However, there was a decrease in cell proliferation upon confinement for all tested cell lines. The soft cell confiner is thus a valuable tool to decipher the effect of long-term confinement and deformation on the biology of cell populations. This tool will be instrumental in deciphering the impact of nuclear and cytoskeletal mechanosensitivity in normal and pathological conditions involving highly confined situations, such as those reported upon aging with fibrosis or during cancer. Graphical abstract O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY A unique tool to analyze the role of long-term effect of mechanical confinement in normal and pathological conditions

biophysics↗