Biology subjects

Levillayer, F.

Publications and source records attributed to Levillayer, F..

5 recordsLinked to original sources

bioRxiv2025

Integration of past caspase activity biases cell elimination in vivo

The fine tuning of apoptosis in epithelia is essential for regulating tissue size, shape, homeostasis and the maintenance of sealing properties. Regulation of cell death is mostly orchestrated by the activation of Caspases, proteases which were long thought to trigger an irreversible engagement in cell death. However, recent data in vivo and in vitro outline numerous non-apoptotic functions of caspases as well as quite ubiquitous sublethal activation of effector caspases during development. Yet, it remains unclear in many instances what drives the bifurcation between cell death engagement and cell survival upon caspase activation. The existence of a caspase activity threshold was generally considered to underpin this binary decision, but this was never assessed quantitatively in vivo especially at the single cell level. Using quantitative live imaging combined with machine learning and optogenetics in the Drosophila pupal notum (a single layer epithelium), we reveal for the first time the existence of a large heterogeneity of caspase sensitivity between cells, as well as the existence of distinct spatial domains with low or high sensitivity to caspases. Using correlative and perturbative experiments, we outline the central role of past exposure to sublethal caspase activity which sensitises cells for apoptosis for several hours. Integrating information about past caspase activation is sufficient to explain most of the global pattern of caspase sensitivity and predict at the single cell level which cells will engage in apoptosis. Finally, we demonstrate that past sublethal caspase activation in a subset of cells is sufficient to bias cell elimination at the clonal and single cell level, thus revealing an alternative mechanism of physiological cell competition. Altogether, this work reveals for the first time the existence of a new layer of apoptosis regulation in vivo downstream of effector caspases which can be developmentally regulated and bias clonal selection and the spatial pattern of cell death.

developmental biology↗

bioRxiv2024

Developmental delay ensures global tissue size robustness upon local induction of apoptosis

The capacity of our tissues to cope with external and internal stress relies on the tight coupling between cell proliferation, cell growth and cell death. This coupling is assumed to be based on compensatory proliferation, where local mitogenic signals and mechanical inputs generated by dying cells promote neighbouring cell proliferation. However, compensatory proliferation was mostly studied in the context of massive death induction, irradiation, surgical tissue ablation or upon genetic perturbation of apoptosis execution. It remains thus unclear whether the same mechanism operates during physiological programmed cell death or upon mild induction of apoptosis, especially in vivo. Here, we use the Drosophila prospective wing (the larval wing disc), to study the impact of local induction of apoptosis on tissue size and proliferation pattern. We first confirmed that the wing could recover its final size and compensate for mild induction of apoptosis. However, using spatial statistics we found surprisingly that local induction of death is not associated with any local increase of proliferation, could it be upon clonal or compartment induction of apoptosis. Compensation is driven instead by a JNK dependant delay of growth and lengthening of the larval stage which is required to reach the final tissue target size. These results suggest that compensation is here driven by a global response rather that a local proliferation induction. Accordingly, while total tissue size is maintained despite local induction of apoptosis, this mechanism fails to correct the local reduction of cell number, hence modulating wing shape and proportion. Overall, this study opens novel perspectives on tissue size regulation and outlines the context-dependency of compensatory mechanisms.

developmental biology↗

bioRxiv2021

Microtubule disassembly by caspases is the rate-limiting step of cell extrusion

Epithelial cell death is essential for tissue homeostasis, robustness and morphogenesis. The expulsion of epithelial cells following caspase activation requires well-orchestrated remodeling steps leading to cell elimination without impairing tissue sealing. While numerous studies have provided insight about the process of cell extrusion, we still know very little about the relationship between caspase activation and the remodeling steps of cell extrusion. Moreover, most studies of cell extrusion focused on the regulation of actomyosin and steps leading to the formation of a supracellular contractile ring. However, the contribution of other cellular factors to cell extrusion has been poorly explored. Using the Drosophila pupal notum, a single layer epithelium where most extrusion events are caspase-dependent, we first showed that the initiation of cell extrusion and apical constriction are surprisingly not associated with the modulation of actomyosin concentration/dynamics. Instead, cell apical constriction is initiated by the disassembly of a medio-apical mesh of microtubules which is driven by effector caspases. We confirmed that local and rapid increase/decrease of microtubules is sufficient to respectively expand/constrict cell apical area. Importantly, the depletion of microtubules is sufficient to bypass the requirement of caspases for cell extrusion. This study shows that microtubules disassembly by caspases is a key rate-limiting steps of extrusion, and outlines a more general function of microtubules in epithelial cell shape stabilisation.

cell biology↗

bioRxiv2020

Robustness of epithelial sealing is an emerging property of local ERK feedbacks driven by cell elimination

While the pathways regulating apoptosis and cell extrusion are rather well described1,2, what regulates the precise spatio-temporal distribution of cell elimination in tissues remains largely unknown. This is particularly relevant for epithelia with high rates of cell elimination, a widespread situation during embryogenesis3-6 and epithelial homeostasis7, where concomitant death of neighbours could impair the maintenance of epithelial sealing. However, the extent to which epithelial tissues can cope with concomitant cell death, and whether any mechanism regulates such occurrence have never been explored so far. Here, using the Drosophila pupal notum (a single layer epithelium) and a new optogenetic tool to trigger caspase activation and cell extrusion, we first show that concomitant death of clusters of at least three cells is sufficient to transiently impair epithelial sealing. Such clustered extrusion was almost never observed in vivo, suggesting the existence of a mechanism preventing concomitant elimination of neighbours. Statistical analysis and simulations of cell death distribution in the notum highlighted a transient and local protective phase occurring near every dying cell. This protection is driven by a transient activation of ERK in the direct neighbours of extruding cells which reverts caspase activation and prevents elimination of cells in clusters. Altogether, this study demonstrates that the distribution of cell elimination in epithelia is an emerging property of transient and local feedbacks through ERK activation which is required to maintain epithelial sealing in conditions of high rate of cell elimination.

developmental biology↗

bioRxiv2018

Competition for space induces cell elimination through compaction-driven ERK downregulation

The plasticity of developing tissues relies on the adjustment of cell survival and growth rate to environmental cues. This includes the effect of mechanical cues on cell survival. Accordingly, compaction of an epithelium can lead to cell extrusion and cell death. This process was proposed to contribute to tissue homeostasis but also to facilitate the expansion of pretumoral cells through the compaction and elimination of the neighbouring healthy cells. However we know very little about the pathways than can trigger apoptosis upon tissue deformation and the contribution of compaction driven death to clone expansion was never assessed in vivo. Using the Drosophila pupal notum and a new live sensor of ERK, we show that tissue compaction induces cell elimination through the downregulation of EGFR/ERK pathway and the upregulation of the pro-apoptotic protein Hid. Those results suggest that the sensitivity of EGFR/ERK pathway to mechanics could play a more general role in the fine tuning of cell elimination during morphogenesis and tissue homeostasis. Secondly, we assessed in vivo the contribution of compaction driven death to pretumoral cell expansion. We found that the activation of the oncogene Ras in clones can also downregulate ERK and activate apoptosis in the neighbouring cells through their compaction, which contributes to Ras clone expansion. The mechanical modulation of EGFR/ERK during growth-mediated competition for space may contribute to tumour progression.

developmental biology↗