Biology subjects

Bellaiche, Y.

Publications and source records attributed to Bellaiche, Y..

15 recordsLinked to original sources

bioRxiv2026

Tissue mechanics sets developmental scaling of collective cell migration

Despite substantial variation in adult size, animals within a species maintain consistent tissue patterns and shapes, a core property known as developmental scaling or size invariance. Developmental scaling has predominantly been attributed to the scaling of morphogen gradients and gene patterns to maintain positional information and cell fate specification1,2. However, development also necessitates collective cell flows that reshape tissues and reposition cells3,4. How these flows adapt to body size remains unclear. By combining quantitative live imaging, experimental perturbations, and physical modeling in the Drosophila thorax epithelium, we address this question in the context of a fundamental process: collective cell migration. We find that migration velocity scales linearly with tissue size, accounting for size-invariant cell positioning. While gene patterning scales with tissue size and modulates force generation, it is not sufficient to ensure proper velocity scaling. Instead, tissue mechanical properties govern the dependence of migration velocity on tissue size, enabling developmental scaling within the physiological range of animal sizes. These findings uncover principles and limits of size invariance by revealing how tissue mechanics sets the scaling behavior of collective cell flows with organismal size.

developmental biology↗

bioRxiv2026

Differential turnover of apicobasal regulators drives emergent mechano-response and shape homeostasis

Epithelial cell shape plays a fundamental role in tissue dynamics. Numerous studies have established how cells drastically change their shape to promote epithelial tissue morphogenesis. However, the mechanisms enabling cells to maintain their shape remain far less understood. Here, leveraging live imaging in Drosophila epithelial tissue and theoretical modeling, we identify an emergent mechano-chemical feedback that ensures junction length and cell shape stability, without requiring a dedicated molecular force sensor. We find that an increase in junction length is associated with a passive dilution of E-Cadherin, followed by an increase in Myosin-II-dependent contractility that reduces junction length. Theoretically, we show that this regulation of junction length generically emerges when negative and positive regulators of contractility have distinct kinetics. Experiments confirm that E-Cadherin acts as a negative regulator with slow turnover. Mechanistically, local dilution of E-Cadherin passively lifts an inhibition on lateral apicobasal polarity components, allowing the RhoGEF Cyst -- with its fast turnover -- to accumulate and increase contractility. Perturbing this feedback results in aberrant cell junction and shape regulation, thereby compromising the ability of the tissue to buffer local mechanical fluctuations and global mechanical stresses. Altogether, we propose that differential turnover between apical and lateral polarity complexes provides an emergent mechano-response for junction length and cell shape homeostasis.

biophysics↗

bioRxiv2026

Membrane lipid composition and endocytosis modulate Wingless release from secreting cells

Wnts are secreted signalling molecules that regulate development and adult homeostasis. Most Wnts carry a lipid moiety that must be shielded from the aqueous environment. In the secretory pathway, this is achieved by a hydrophobic tunnel in Wntless, a multipass transmembrane protein. However, the Wnt lipid moiety must be released from Wntless before Wnts can engage with Frizzled receptors on receiving cells. Here we address the cell biological basis of Wnt-Wntless dissociation, using as a model the secretion of Drosophila Wingless in wing primordia. Super-resolution microscopy shows that Wingless first reaches the apical surface before being re-internalized to reach, without Wntless, specialized Rab7/Rab4-positive endosomes. From there Wingless traffics to the basolateral membrane where it can engage with glypicans to form a basolateral gradient. Acute inhibition of endocytosis, either with a temperature-sensitive dynamin mutant or a novel optogenetic means of inhibiting clathrin, leads to apical Wingless release in abnormal punctae devoid of Wntless, suggesting that Wingless-Wntless dissociation commences at the apical surface, perhaps because of a distinct lipid composition there. Indeed, similar looking punctae are produced upon genetic abrogation of the ceramide synthase Schlank, specifically in Wingless-producing cells. These punctae resemble insoluble aggregates that form in vitro upon detergent removal. Accordingly, punctae formation can be prevented by shielding the Wingless lipid, in vivo with excess Dally-like protein (Dlp) or in vitro with liposomes. Our results show that membrane lipid composition modulates the orderly transfer of Wingless lipid from Wntless to the inner endosomal surface thus preventing aggregation and ensuring seamless secretion in the basolateral space.

cell biology↗

bioRxiv2025

Spatial inhibition of RhoA by RhoGAP15B promotes protrusive activity during collective cell migration

The Rho family GTPases RhoA, Rac1 and Cdc42 are well established regulators of collective migration by driving the formation of cellular protrusions and by regulating actomyosin contraction and adhesion. However, how their activation and inhibition are spatially and temporally coordinated remains unclear. Using GFP knock-in lines, we systematically characterized the localization patterns of all Drosophila RhoGEFs (activators) and RhoGAPs (inhibitors) in border cells, an in vivo model of collective migration. We have further combined RNAi screening with GFP-based validation of depletion efficiency to assess the functional significance of those RhoGEF/GAPs expressed in border cells. This identified RhoGAP15B as a localized inhibitor of RhoA activity at the border cell cortex. RhoGAP15B regulates cluster morphology and is enriched at the leading cell front, where it restrains actomyosin contractility to promote protrusive behavior. Our findings reveal RhoGAP15B as a key spatial RhoA regulator and highlight that patterned RhoGAP and RhoGEF activities are essential for coordinating cortical contraction and protrusion dynamics during collective migration.

cell biology↗

bioRxiv2025

Tissue mechanics and systemic signaling safeguard epithelial tissue against spindle misorientation.

Multicellular organisms possess conserved safeguard mechanisms that ensure the maintenance of tissue integrity. Exploring these mechanisms has proven instrumental in understanding how tissues robustly develop and prevent tumor initiation. Here, we investigate how epithelial tissues preserve their architecture and cell number in the face of spindle mis-orientation. Spindle mis-orientation, due to the lack of spindle pulling forces, centrosomes, or mitotic rounding, can cause epithelial cells to be mispositioned within or outside the tissue, leading to significant cell loss. By inducing spindle mis-orientation in Drosophila epithelial tissue, we first found that acentrosomal microtubules and cell contractility prevent excessive epithelial cell loss by enabling mispositioned cells to reintegrate into the epithelium. However, this mechanism alone is insufficient to maintain the total epithelial cell number. We uncovered that epithelial mechanics and cell size sensing monitor and compensate for epithelial cell loss predominantly by reducing physiological apoptosis through Hippo/YAP signaling. Lastly, we found that systemic TNF signaling protects the organism by eliminating potentially harmful non-reintegrating cells. Overall, our results delineate the complementary roles of mechanics and systemic signaling in controlling cell number and position at both tissue and organismal levels.

developmental biology↗

bioRxiv2025

Toll receptors mediate tissue intrinsic surveillance against aberrant cells by detecting cell fate aberrations

Tissue-intrinsic surveillance systems play an important role in maintaining tissue health by detecting and eliminating aberrant cells. One such system, interface surveillance, is activated by differences in cell fate programs between neighboring cells. Activation of interface surveillance drives separation and elimination of aberrant cells by recruitment of actin regulators and Myosin II to neighboring cell contacts, as well as activation of JNK signaling and apoptosis in cells at this interface. Here, we uncover the role of long Toll receptors (Toll-2, Toll-6, Toll-7, Toll-8) as key mediators of interface surveillance in Drosophila wing imaginal discs. Using genetic mosaics combined with spatial mapping of Toll receptor expression patterns, we demonstrate that differences in long Toll receptor expression levels between neighboring cells trigger all hallmark responses of interface surveillance. This response is position-dependent and relies on the comparison of expression levels established by cell-fate-specifying programs. Specifically, we show that the expression of long Toll receptors is regulated by multiple fate-patterning pathways, giving rise to a combinatorial cell surface code that is deregulated in developmentally aberrant or oncogenic cells. Remarkably, Toll receptor-mediated surveillance operates independently of canonical NF-{kappa}B signaling, and rather mirrors a distinct role of long Toll receptors in modulating cell-cell affinity via actomyosin dynamics during early embryogenesis. Our findings identify long Toll receptors as integrators of developmental patterning and tissue homeostasis mechanisms and provide insights into how tissues detect and respond to potentially oncogenic mutations that misregulate cell fate specification pathways.

cell biology↗

bioRxiv2025

Drosophila Toll-2 controls homeotic domain formation and timing of folding

Tissue compartmentalization is a fundamental feature of animal development, crucial for determining cell fate, growth, and organ morphogenesis. Hox genes play essential and conserved roles in specifying homeotic compartments along the antero-posterior axis of the body. Despite extensive characterization of homeotic gene regulation, the mechanisms underlying the formation, maintenance, and reshaping of homeotic compartments during development remain incompletely understood. Here, we investigate the role of the Toll-2 receptor in the formation and folding of the Deformed (Dfd) homeotic compartment, which produces the neck of adult Drosophila. We show that Toll-2 is essential for properly forming the bilateral Dfd compartment through the fusion of the two eye-antennal imaginal discs. Additionally, we find that Toll-2 regulates the timing of neck morphogenesis by promoting cell apoptosis and cell-cell rearrangements preceding neck folding. Last, we establish that Toll-2 independently and sequentially governs both homeotic compartment formation and the timing of its morphogenesis via PI3K and Src signaling, respectively. Altogether, our findings provide novel insights into the spatiotemporal regulation of homeotic compartment development.

developmental biology↗

bioRxiv2024

Adhesion-Controlled Mechanics of the Glial Niche Regulate Neural Stem Cell Proliferative Potential

Controlled proliferation of neural stem cells (NSCs) builds a functional nervous system during development. While their cellular niche is recognized as a signalling hub, the contribution of its structure and mechanics in regulating neurogenesis remains unexplored. The Drosophila larval central nervous system contains self-renewing NSCs in close contact with cortex glial cells. Transcriptomics identified a triad of immunoglobulin superfamily cell adhesion molecules (Dpr10/Dpr6 in glia and DIP- in NSCs) which physically and mechanically connect the NSC and glial membranes, acting as mechanoregulators. Their disruption increases glial cortical tension, causing non-autonomous mitotic defects in NSCs, characterized by abnormal spindle morphologies and impaired mitotic progression. Additionally, elevated glial tensile forces increase Lamin content in NSCs, a protective response also resulting in nuclear deformation. Ultimately NSC proliferative potential and genome integrity are compromised. Our study reveals that the native mechanical properties of the niche are transmitted to NSCs and regulate their function. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=156 SRC="FIGDIR/small/628019v1_ufig1.gif" ALT="Figure 1"> View larger version (47K): org.highwire.dtl.DTLVardef@18137f8org.highwire.dtl.DTLVardef@819740org.highwire.dtl.DTLVardef@1f0ed0forg.highwire.dtl.DTLVardef@5ba0e4_HPS_FORMAT_FIGEXP M_FIG C_FIG

developmental biology↗

bioRxiv2024

The Dystrophin-Dystroglycan complex ensures cytokinesis efficiency in Drosophila epithelia

Cytokinesis physically separates daughter cells at the end of cell division. This step is particularly challenging for epithelial cells, which are connected to their neighbors and to the extracellular matrix by transmembrane protein complexes. To systematically evaluate the impact of the cell adhesion machinery on epithelial cytokinesis efficiency, we performed an RNAi-based modifier screen in the Drosophila follicular epithelium. Strikingly, this unveiled adhesion molecules and transmembrane receptors that facilitate cytokinesis completion. Among these is Dystroglycan, which connects the extracellular matrix to the cytoskeleton via Dystrophin. Live imaging revealed that Dystrophin and Dystroglycan become enriched in the ingressing membrane, below the cytokinetic ring, during and after ring constriction. Using multiple alleles, including Dystrophin isoform-specific mutants, we show that Dystrophin/Dystroglycan localization is linked with unanticipated roles in regulating cytokinetic ring contraction and in preventing membrane regression during the abscission period. Altogether, we provide evidence that, rather than opposing cytokinesis completion, the machinery involved in cell-cell and cell-matrix interactions has also evolved functions to ensure cytokinesis efficiency in epithelial tissues.

cell biology↗

bioRxiv2022

Systematic characterization of Drosophila RhoGEF/GAP localizations uncovers regulators of mechanosensing and junction formation during epithelial cell division.

Cell proliferation is central to epithelial tissue development, repair and homeostasis. During cell division, small RhoGTPases control both actomyosin dynamics and cell-cell junction remodelling to faithfully segregate the duplicated genome while maintaining tissue polarity and integrity. To decipher the mechanisms of RhoGTPases spatiotemporal regulation during epithelial cell division, we generated a transgenic fluorescently tagged library for Drosophila Rho Guanine exchange factors (GEF) and GTPase activating proteins (GAP), and systematically characterized their endogenous distributions by time- lapse microscopy. Thereby, we unveiled candidate regulators of the interplay between actomyosin and junctional dynamics during epithelial cell division. Building on these findings, we uncovered that during cytokinesis, Cysts and RhoGEF4 play sequential roles in mechanosensing and de novo junction formation, respectively. We foresee that the RhoGEF/GAP library will be a key resource to understand the broad range of biological processes regulated by RhoGTPases.

developmental biology↗

bioRxiv2022

Apical size and deltaA expression predict adult neural stem cell decisions along lineage progression

The maintenance of neural stem cells (NSCs) in the adult brain depends on their activation frequency and division mode. We use long-term intravital imaging of NSCs in the zebrafish adult telencephalon to link activation and division mode with predictive cellular and molecular parameters. We reveal that apical surface area and expression of the Notch ligand DeltaA predict NSC activation frequency, while deltaA expression marks NSC commitment to neurogenesis. We also find that deltaA-negative NSCs constitute the bona fide self-renewing NSC pool and systematically engage in asymmetric divisions generating a self-renewing deltaAneg and a neurogenic deltaApos NSC. Finally, modulation of Notch signaling during imaging indicates that the prediction of activation frequency by apical size, and the asymmetric divisions of deltaAneg NSCs, are functionally independent of Notch. These results provide dynamic qualitative and quantitative readouts of NSC lineage progression in vivo and support a hierarchical organization of NSCs in differently fated sub-populations.

neuroscience↗

bioRxiv2022

Homeotic compartment curvature and tension control spatiotemporal folding dynamics.

Shape is a conspicuous and fundamental property of biological systems entailing the function of organs and tissues. While much emphasis has been put on how tissue tension and mechanical properties drive shape changes, whether and how a given tissue geometry influences subsequent morphogenesis remains poorly characterized. Here, we explored how curvature, a key descriptor of tissue geometry, impinges on the dynamics of epithelial tissue invagination. We found that the morphogenesis of the fold separating the adult Drosophila head and thorax segments is driven by the invagination of the Deformed (Dfd) homeotic compartment. Dfd controls invagination by modulating actomyosin organization and in-plane epithelial tension via the Tollo and Dystroglycan receptors. By experimentally introducing curvature heterogeneity within the homeotic compartment, we established that a curved tissue geometry converts the Dfd-dependent in-plane tension into an inward force driving folding. Accordingly, the interplay between in-plane tension and tissue curvature quantitatively explains the spatiotemporal folding dynamics. Collectively, our work highlights how genetic patterning and tissue geometry provide a simple design principle driving folding morphogenesis during development.

developmental biology↗

bioRxiv2021

Skin-resident immune cells actively coordinate their distribution with epidermal cells during homeostasis

Our organs consist of multiple cell types that ensure proper architecture and function. How different cell types coexist and interact to maintain their homeostasis in vivo remain elusive. The skin epidermis comprises mostly epithelial cells, but also harbors Langerhans cells (LCs) and Dendritic Epidermal T cells (DETCs). In response to injury or infection, LCs and DETCs become activated and play critical immunological roles. During homeostasis, they coexist with epithelial cells in the basal layer of the epidermis. Whether, and how, distributions of LCs and DETCs are regulated during homeostasis is unclear. Here, we addressed this question by tracking LCs, DETCs and epithelial basal cells over time within the skin of live adult mice. We show that LCs and DETCs maintain their overall position despite continuous turnover of neighboring basal epithelial stem cells. Moreover, LCs and DETCs rapidly and maximally explore basal epithelial cell junctions through their dendritic extensions. Altering the epithelial cell density triggers corresponding changes in the immune cell density, but not vice versa, suggesting that epithelial cells determine immune tissue composition in the epidermis. Moreover, LCs and DETCs are organized in a tiling pattern that is actively maintained. When LCs or DETCs are ectopically removed, neighboring epidermal LCs or DETCs, respectively, move into the emptied spaces and re-establish the tiling pattern. Finally, LCs require the GTPase Rac1 to maintain their positional stability, density and tiling pattern. Overall, we discovered that epidermal cells regulate the density of immune cells during homeostasis, and that immune cells actively maintain a non-random spatial distribution, reminiscent of neuronal self-avoidance. We propose that these cellular mechanisms provide the epidermis with an optimal response to environmental insults.

cell biology↗

bioRxiv2020

Frizzled-dependent Planar Cell Polarity without Wnt Ligands

Planar cell polarity (PCP) organizes the orientation of cellular protrusions and migratory activity within the tissue plane. PCP establishment involves the subcellular polarization of core PCP components. It has been suggested Wnt gradients could provide a global cue that coordinates local PCP with tissue axes. Here we dissect the role of Wnt ligands in the orientation of hairs of Drosophila wings, an established system for study of PCP. We found that PCP was normal in quintuple mutant wings that rely solely on membrane-tethered Wingless for Wnt signaling, suggesting that a Wnt gradient is not required. We then used a nanobody-based approach to trap Wntless in the endoplasmic reticulum, and hence prevent all Wnt secretion, specifically during the period of PCP establishment. PCP was still established. We conclude that, even though Wnt ligands could contribute to PCP, they are not essential, and another global cue must exist for tissue-wide polarization.

developmental biology↗

bioRxiv2018

Tricellular junction proteins promote disentanglement of daughter and neighbour cells during epithelial cytokinesis

In epithelial tissue, new cell-cell junctions are formed upon cytokinesis. To understand junction formation during cytokinesis, we explored in Drosophila epithelium, de novo formation of tricellular septate junctions (TCJs). We found that upon midbody formation, the membranes of the two daughter cells and of the neighbouring cells located below the adherens junction (AJ) remain entangled in a 4-cell structure apposed to the midbody. The septate junction protein Discs-Large and components of the TCJ, Gliotactin and Anakonda accumulate in this 4-cell structure. Subsequently, a basal movement of the midbody parallels the detachment of the neighbouring cell membranes from the midbody, the disengagement of the daughter cells from their neighbours and the reorganisation of TCJs between the two daughter cells and their neighbouring cells. While the movement of midbody is independent of the Alix and Shrub abscission regulators, the loss of Gliotactin or Anakonda function impedes both the resolution of the connection between the daughter-neighbour cells and midbody movement. TCJ proteins therefore control an additional step of cytokinesis necessary for the disentanglement of the daughter cells and their neighbours during cytokinesis.

developmental biology↗