Biology subjects

Lecuit, T.

Publications and source records attributed to Lecuit, T..

14 recordsLinked to original sources

bioRxiv2026

Encoding neuronal shape in the stochastic dynamics of branching processes

Cell shape critically influences function, yet how complex and reproducible morphologies emerge from stochastic cellular dynamics remains unclear. Here, we investigate dendritic morphogenesis of two classes of Drosophila mechanosensory neurons with contrasting architectures, combining in vivo live imaging, quantitative analysis, cytoskeletal perturbations, and computational modeling. We show that despite sharing similar local stochastic branching rules, the two classes exhibit divergent growth dynamics that cannot be explained by standard, diffusive growth models. This discrepancy arises because Class I neurons display subdiffusive branch dynamics over long timescales, unlike Class IV. Based on these findings, we develop a minimal model with only four parameters that separates short-and long-term branch behaviors, and successfully recapitulates growth dynamics and final morphologies in both classes. Cytoskeletal perturbations reveal a functional separation between actin, which drives short-term exploratory branch fluctuations and arbor expansion, and microtubules, which tune long-term branch diffusivity and determine class-specific morphology. Together, these results establish a parsimonious, generalizable framework linking local cytoskeletal regulation to global neuronal architecture and reveal how stochastic dynamics encode reproducible cell shapes.

biophysics↗

bioRxiv2025

Spatial patterning of contractility by a mechanogen gradient underlies Drosophila gastrulation

During development cell deformations are spatially organized, however, how cellular mechanics is spatially controlled is unclear. Spatial control of cell identity often determines local cellular mechanics in a two-tiered mechanism (1). Theoretical studies also proposed that molecular gradients, so called "mechanogens", spatially control mechanics (2, 3). We report evidence of such a "mechanogen" required for Drosophila gastrulation. We show that the GPCR ligand Fog, expressed in the posterior endoderm (4-6), diffuses and acts in a concentration-dependent manner to activate actomyosin contractility at a distance during a wave of tissue invagination. While Fog is uniformly distributed in the extracellular space, it forms a surface-bound gradient that activates Myosin-II via receptor oligomerization. This activity gradient self-renews as the wave propagates and is shaped by both receptor endocytosis and a feedback mechanism involving adhesion to the vitelline membrane by integrins. This exemplifies how chemical, mechanical and geometrical cues underly the emergence of a self-organized mechanogen activity gradient.

developmental biology↗

bioRxiv2024

Mechanical regulation of cuboidal-to-squamous epithelial transition in the Drosophila developing wing

Growing tissues are constantly exposed to mechanical stresses that lead to deformations at the cell and tissue scale. In epithelial organs, cells form monolayers whose thickness can change dramatically during development. Here, we address how cell shape changes in the peripodial epithelium of the Drosophila wing disc emerge from the interplay of basement membrane properties with tissue-extrinsic mechanical stress. We show that tissue-extrinsic stress arising from disc proper bending elastically deforms central peripodial cells and induces a cuboidal-to-squamous epithelial transition. In contrast, a rigid basement membrane shields peripheral hinge cells from this bending stress and causes a cuboidal-to-columnar transition. These inverse shape transitions are further amplified by selective shearing of central cells due to coupling via the apical extracellular matrix protein Dumpy. These findings point to a pivotal role of the basement membrane and inter-tissue coupling in the emergence of stress patterns and cell deformations during organ growth.

developmental biology↗

bioRxiv2023

Mechanical regulation of substrate adhesion and de-adhesion drives a cell contractile wave during tissue morphogenesis

During morphogenesis tissue-scale forces drive large-scale deformations, yet how these forces arise from the local interplay between cellular contractility and adhesion is poorly understood. In the posterior endoderm of Drosophila embryos, a self-organized tissue-scale wave of actomyosin contractility and cell invagination is coupled with adhesion to the surrounding vitelline membrane to drive the polarized tissue deformation. We report here that this process emerges at the subcellular level from the mechanical coupling between Myosin-II activation and sequential adhesion/de-adhesion to the vitelline membrane. At the wavefront, integrin focal complexes anchor the actin cortex to the vitelline membrane and promote activation of Myosin-II, which in turn enhances adhesion in a positive feedback loop. Subsequently, upon detachment, cortex contraction and advective flow further amplify Myosin-II levels. Prolonged contact with the vitelline membrane increases the duration of the integrin-Myosin-II feedback, integrin adhesion and thus slows down cell detachment and wave propagation of the invagination. Finally, we show that the angle of cell detachment changes as a function of the strength of adhesion and modifies the tensile forces required for detachment to maintain wave propagation. This illustrates how the tissue-scale wave arises from subcellular mechanochemical feedbacks and tissue geometry.

developmental biology↗

bioRxiv2023

Evolutionarily conserved role of serotonin signaling in regulating actomyosin contractility during morphogenesis

Serotonin is a neurotransmitter that signals through 5-HT receptors to control key functions in the nervous system. Serotonin receptors are also ubiquitously expressed in various organs and have been detected in embryos of different organisms. Potential morphogenetic functions of serotonin signaling have been proposed based on pharmacological studies but a mechanistic understanding is still lacking. Here, we uncover a role of serotonin signaling in axis extension of Drosophila embryos by regulating MyosinII (MyoII) activation, cell contractility and cell intercalation. We find that serotonin and serotonin receptors 5HT2A and 5HT2B form a signaling module that quantitatively regulates the amplitude of planar polarized MyoII contractility specified by Toll receptors and the GPCR Cirl. Remarkably, serotonin signaling also regulates actomyosin contractility at cell junctions, cellular flows and epiblast morphogenesis during chicken gastrulation. This phylogenetically conserved mechanical function of serotonin signaling in regulating actomyosin contractility and tissue flow reveals an ancestral role in morphogenesis of multicellular organisms.

developmental biology↗

bioRxiv2022

Growth anisotropy of the extracellular matrix drives mechanics in a developing organ

The final size and shape of organs results from volume expansion by growth and shape changes by contractility. Complex morphologies arise from differences in growth rate between tissues. We address here how differential growth drives epithelial thickening and doming during the morphogenesis of the growing Drosophila wing imaginal disc. We report that 3D morphology results from elastic deformation due to differential growth between the epithelial cell layer and its enveloping extracellular matrix (ECM). Furthermore, the ECM envelope exhibits differential growth anisotropy (i.e. anisotropic expansion in 3D), growing in-plane on one side, but out of plane on the other side. The elasticity, anisotropy and morphogenesis is fully captured by a mechanical bilayer model. Moreover, differential expression of the Matrix metalloproteinase MMP2 controls growth anisotropy of the two ECM layers. This study shows that the ECM is a controllable mechanical constraint whose intrinsic growth anisotropy directs tissue morphogenesis in a developing organ.

developmental biology↗

bioRxiv2022

Genetic and geometric heredity interact to drive polarized flow in the Drosophila embryo

Tissue flow during morphogenesis is commonly driven by local constriction of cell cortices, which is caused by activation of actomyosin contractility. This can lead to long-range flows due to tissue viscosity. However, in the absence of cell-intrinsic polarized forces or polarity in forces external to the tissue, these flows must be symmetric and centered around the region of contraction. Polarized tissue flows have been previously demonstrated to arise from the coupling of such contractile flows to points of increased friction or adhesion to external structures. However, we show with experiments and modeling that the onset of polarized tissue flow in early Drosophila morphogenesis occurs independent of adhesion and is instead driven by a geometric coupling of apical actomyosin contractility to tissue curvature. Particularly, the onset of polarized flow is driven by a mismatch between the position of apical myosin activation and the position of peak curvature at the posterior pole of the embryo. Our work demonstrates how genetic and geometric information inherited from the mother interact to create polarized flow during embryo morphogenesis.

developmental biology↗

bioRxiv2020

Self-organized Toll-8/Cirl GPCR asymmetry drives planar polarized cell contractility

During development, interfaces between cells with distinct genetic identities elicit signals to organize local cell behaviors driving tissue morphogenesis. The Drosophila embryonic axis extension requires planar polarized enrichment of Myosin-II powering oriented cell intercalations. Myosin-II levels are quantitatively controlled by G protein-coupled receptor (GPCR) signaling whereas Myosin-II polarity requires patterned expression of several Toll receptors. How Toll receptors polarizes Myosin-II, and how this involves GPCRs, remain unknown. Here we report that differential expression of a single Toll receptor, Toll-8, polarizes Myosin-II via a novel binding partner, the adhesion GPCR Cirl/Latrophilin. Asymmetric expression of Cirl is sufficient to enrich Myosin-II and Cirl localization is asymmetric at Toll-8 expression boundaries. Exploring the process dynamically, we reveal that Toll-8 and Cirl exhibit mutually dependent planar polarity in response to quantitative differences in Toll-8 expression between neighboring cells. Collectively, we propose that a novel cell surface protein complex Toll-8/Cirl self-organizes to generate local asymmetric interfaces essential for planar polarization of contractile interfaces.

developmental biology↗

bioRxiv2019

DISTINCT ACTIN-DEPENDENT NANOSCALE ASSEMBLIES UNDERLIE THE DYNAMIC AND HIERARCHICAL ORGANIZATION OF E-CADHERIN.

Intercellular adhesion mediated by E-cadherin is pivotal in maintaining epithelial tissue integrity and for tissue morphogenesis. Adhesion requires homophilic interactions between extracellular domains of E-cadherin molecules from neighboring cells. The interaction of its cytoplasmic domains with the cortical acto-myosin network, appears to strengthen adhesion, although, it is unclear how cortical actin affects the organization and function of E-cadherin dynamically. Here we use the ectopic expression of Drosophila E-cadherin (E-cad) in larval hemocytes, which lack endogenous E-cad, to recapitulate functional cell-cell junctions in a convenient model system. We used fluorescence emission anisotropy-based microscopy and Fluorescence Correlation Spectroscopy (FCS) to probe the nanoscale organization of E-cad. We find that E-cad at cell-cell junctions in hemocytes exhibits a clustered trans-paired organization, similar to that reported for the adherens junction in the developing embryonic epithelial tissue. Further, we find that extra-junctional E-cad is also organized as relatively immobile nanoclusters as well as diffusive and more loosely packed oligomers and monomers. These oligomers are promoted by cis-interactions of the ectodomain and, strikingly, their growth is constantly counteracted by cortical actomyosin. Oligomers in turn assist in generating nanoclusters that are stabilized by cortical acto-myosin. Thus, actin remodels oligomers and stabilizes nanoclusters, revealing a requirement for actin in the dynamic organization of E-cad at the nanoscale. This dynamic organization is also present at cell-cell contacts (junction), and its disruption affects junctional integrity in the hemocyte system, as well as in the embryo. Our observations uncover a hierarchical mechanism for the nanoscale organization of E-cad, which is necessary for dynamic adhesion and maintaining junctional integrity in the face of extensive remodeling.

cell biology↗

bioRxiv2019

Assembly of a persistent apical actin network by the formin Frl/Fmnl tunes epithelial cell deformability

Tissue remodeling during embryogenesis is driven by the apical contractility of the epithelial cell cortex. This behavior arises notably from Rho1/Rok induced transient accumulation of non-muscle myosin II (MyoII pulses) pulling on actin filaments (F-Actin) of the medio-apical cortex. While recent studies begin to highlight the mechanisms governing the emergence of Rho1/Rok/MyoII pulsatility in different organisms, little is known about how the F-Actin organization influences this process. Focusing on Drosophila ectodermal cells during germband extension and amnioserosa cells during dorsal closure, we show that the medio-apical actomyosin cortex consists of two entangled F-Actin subpopulations. One exhibits pulsatile dynamics of actin polymerization in a Rho1 dependent manner. The other forms a persistent and homogeneous network independent of Rho1. We identify the Frl/Fmnl formin as a critical nucleator of the persistent network since modulating its level, in mutants or by overexpression, decreases or increases the network density. Absence of this network yields sparse connectivity affecting the homogeneous force transmission to the cell boundaries. This reduces the propagation range of contractile forces and results in tissue scale morphogenetic defects. Our work sheds new lights on how the F-Actin cortex offers multiple levels of regulation to affect epithelial cells dynamics.

developmental biology↗

bioRxiv2019

Distinct RhoGEFs activate apical and junctional actomyosin contractility under control of G proteins during epithelial morphogenesis

Small RhoGTPases and Myosin-II direct cell shape changes and movements during tissue morphogenesis. Their activities are tightly regulated in space and time to specify the desired pattern of contractility that supports tissue morphogenesis. This is expected to stem from polarized surface stimuli and from polarized signaling processing inside cells. We examined this general problem in the context of cell intercalation that drives extension of the Drosophila ectoderm. In the ectoderm, G protein coupled receptors (GPCRs) and their downstream heterotrimeric G proteins (G and G{beta}{gamma}) activate Rho1 both medial-apically, where it exhibits pulsed dynamics, and at junctions, where its activity is planar polarized (Kerridge et al., 2016; Munjal et al., 2015). However, the mechanisms responsible for polarizing Rho1 activity are unclear. In particular, it is unknown how Rho1 activity is controlled at junctions. We report a division of labor in the mechanisms of Rho1 activation in that distinct guanine exchange factors (GEFs), that serve as activators of Rho1, operate in these distinct cellular compartments. RhoGEF2 acts uniquely to activate medial-apical Rho1. Although RhoGEF2 is recruited both medial-apically and at junctions by G12/13-GTP, also called Concertina (Cta) in Drosophila, its activity is restricted to the medial-apical compartment. Furthermore, we characterize a novel RhoGEF, p114RhoGEF/Wireless (Wrl), and report its requirement for cell intercalation in the extending ectoderm. p114RhoGEF/Wireless activates Rho1 specifically at junctions. Strikingly it is restricted to adherens junctions and is under G{beta}13F/G{gamma}1 control. G{beta}13F/G{gamma}1 activates junctional Rho1 and exerts quantitative control over planar polarization of Rho1. In particular, overexpression of G{beta}13F/G{gamma}1 leads to hyper planar polarization of Rho1 and MyoII. Finally, we found that p114RhoGEF/Wireless is absent in the mesoderm, arguing for a tissue-specific control over junctional Rho1 activity. These results shed light on the mechanisms of polarization of Rho1 activity in different cellular compartments and reveal that distinct GEFs are sensitive tuning parameters of cell contractility in remodeling epithelia.

developmental biology↗

bioRxiv2018

Transcriptional initiation and mechanically driven self-propagation of a tissue contractile wave during axis elongation

Tissue morphogenesis emerges from coordinated cell shape changes driven by actomyosin contraction1, 2. Spatial patterns of gene expression regionalize and polarize cell behaviours, such as apical constriction in the ventral mesoderm and cell intercalation in the lateral ectoderm of Drosophila3. Thus, tissue dynamics is largely governed genetically. Actomyosin contractile networks drive cell and tissue-level shape changes and can respond to mechanical stimuli 4-9. However how genetic information and mechanical control drive tissue-level morphogenesis is not well understood. Here we report two phases and modalities of Rho1 and non-muscle MyosinII (MyoII) activation in the Drosophila posterior endoderm. First, Rho1/MyoII are induced apically in a spatially restricted primordium region via localized transcription of the GPCR ligand Fog. Second, a tissue-scale travelling wave of Rho1/MyoII activation and cell invagination progresses anteriorly across the dorsal epithelium at a constant speed of 1 cell every 3 minutes. Remarkably, the MyoII wave does not require sustained gene transcription, and is also insensitive to perturbations in the level and pattern of Fog expression. Thus, while fog transcription initiates Rho1/MyoII activation in the primordium, Fog delivery does not govern wave dynamics. Instead, perturbing the mechanical environment of the endoderm impaired MyoII wave dynamics. MyoII inhibition blocked acute Rho1 activation and propagation, suggesting that MyoII contractility provides both local feedback amplification and spatial coupling necessary for wave progression. Finally, we identify a cycle of 3D cell deformations that link MyoII activation and invagination in one row of cells to vitelline membrane attachment, apical spreading, MyoII activation and invagination in the next row, to drive anterior progression of the invagination wave. Thus endoderm morphogenesis emerges from local transcriptional initiation and a mechanically driven travelling cycle of cell contraction and deformation.

developmental biology↗

bioRxiv2018

Two contractile pools of actomyosin distinctly load and tune E-cadherin levels during morphogenesis

During epithelial morphogenesis, cell contacts (junctions) are constantly remodeled by mechanical forces that work against adhesive forces. E-cadherin complexes play a pivotal role in this process by providing persistent cell adhesion and by transmitting mechanical tension. In this context, it is unclear how mechanical forces affect E-cadherin adhesion and junction dynamics.\n\nDuring Drosophila embryo axis elongation, Myosin-II activity in the apico-medial and junctional cortex generates mechanical forces to drive junction remodeling. Here we report that the ratio between Vinculin and E-cadherin intensities acts as a ratiometric readout for these mechanical forces (load) at E-cadherin complexes. Medial Myosin-II loads E-cadherin complexes on all junctions, exerts tensile forces, and increases levels of E-cadherin. Junctional Myosin-II, on the other hand, biases the distribution of load between junctions of the same cell, exerts shear forces, and decreases the levels of E-cadherin. This work suggests distinct effects of tensile versus shear stresses on E-cadherin adhesion.

cell biology↗

bioRxiv2017

Viscoelastic dissipation stabilizes cell shape changes during tissue morphogenesis

Tissue morphogenesis relies on the production of active cellular forces. Understanding how such forces are mechanically converted into cell shape changes is essential to our understanding of morphogenesis. Here we use Myosin II pulsatile activity during Drosophila embryogenesis to study how transient forces generate irreversible cell shape changes. Analyzing the dynamics of junction shortening and elongation resulting from Myosin II pulses, we find that long pulses yield less reversible deformations, typically a signature of dissipative mechanics. This is consistent with a simple viscoelastic description, which we use to model individual shortening and elongation events. The model predicts that dissipation typically occurs on the minute timescale, a timescale commensurate with that of force generation by Myosin II pulses. We test this estimate by applying time-controlled forces on junctions with optical tweezers. Our results argue that active junctional deformation is stabilized by dissipation. Hence, tissue morphogenesis requires coordination between force generation and dissipation.

developmental biology↗