Biology subjects

Corson, F.

Publications and source records attributed to Corson, F..

8 recordsLinked to original sources

bioRxiv2025

Live imaging and functional characterization of the avian hypoblast redefine the mechanisms of primitive streak induction

In birds and mammals, the formation of the primitive streak, the hallmark of the primary axis and site of gastrulation, is thought to occur when an anterior displacement of the hypoblast (visceral endoderm in mice) lifts its inhibition on the posterior epiblast, enabling the activation of NODAL signaling. Although the anterior movement of the murine visceral endoderm is well documented, the dynamics of the avian hypoblast remain poorly understood. Here, using live imaging and quantitative image analysis, we find that the hypoblast is mechanically coupled to the epiblast and does not migrate away from its posterior end. Instead, the hypoblast moves and deforms passively, in response to the forces transmitted from the epiblast that shape the primitive streak, after its induction. Furthermore, we show that the posterior hypoblast does not exert an inhibitory effect on the epiblast but instead expresses NODAL, which activates primitive streak formation. NODAL concomitantly regulates gene expression in the hypoblast, patterning it along the anteroposterior axis. Our results thus redefine how the primary axis is established in avians, demonstrating that the displacement of the hypoblast and its concomitant anteroposterior patterning are consequences -- rather than drivers -- of primitive streak induction, downstream of NODAL signaling. Essential summaryNODAL asymmetric expression in the hypoblast activates primitive streak formation in the avian embryo.

developmental biology↗

bioRxiv2025

Direct measurements of active forces and material properties unveil the active mechanics of early embryogenesis

Despite progress in probing tissue mechanics, direct long-term measurements in live embryonic epithelia are lacking. This limits our understanding of amniote embryonic morphogenesis, which takes place over hours or days. Here, we introduce a combined technological and analytical framework to directly measure active forces and material properties in developing quail embryos, in a minimally invasive way. We find that the embryonic epithelium behaves elastically on short timescales with a modulus [~] 2 nN {middle dot} m-1 but flows over longer timescales with a viscosity [~] 4 N {middle dot} s {middle dot} m-1, and that both properties are under active regulation. Notably, we demonstrate that cell division is an active epithelial fluidizer, with division rates correlating with tissue fluidity. This fluidization is crucial for the emergence of the primary embryonic axis, which we show is shaped by a force [~] 2 N. Altogether, our approach delivers a complete and quantitative view of early embryonic mechanics, and opens new avenues for biomechanical studies in live embryos and tissues.

developmental biology↗

bioRxiv2024

Quantitative guiding of developmental cell fate transitions using gene-free modelling

During development, cells gradually assume specialized fates via changes of transcriptional dynamics in thousands of genes. Landscape modeling approaches, which abstract from the underlying gene regulatory networks and reason in a low-dimensional phenotypic space, have been remarkably successful in explaining terminal fate outcomes. However, their implications for the dynamics of fate acquisition have so far not been tested in vivo. Here we combine a landscape model for C. elegans vulval fate patterning with temporally controlled perturbations of EGF and Notch signaling in vivo using temperature-sensitive mutant alleles. We show that this approach quantitatively predicts non-intuitive fate outcomes and pathway epistasis effects. We further infer how cell fate transitions can be guided towards specific outcomes through timed pulses of signaling activity and verify these model predictions experimentally. Our results highlight the predictive power of landscape models and illustrate a new approach to quantitatively guide cell fate acquisition in a developmental context.

developmental biology↗

bioRxiv2024

Pulsatile dynamics propagate crystalline order in the developing Drosophila eye

Pattern formation in developing tissues often involves self-organization guided by positional information. In most tissues, however, its dynamics, and therefore the underlying logic, remain unknown. Examining self-organized patterning of the fly eye, we combine experiments and modeling to elucidate how rows of light-receiving units emerge in the wake of a traveling differentiation front to form a crystal-like array. Live imaging of the proneural factor Atonal reveals unanticipated oscillations at the front, which are produced by the successive activation of two distinct enhancers and associated with pulsatile Notch signaling. Our observations are inconsistent with current models of eye patterning, whereby each row of differentiating cells provides a negative template for the next. Instead, they inform a new relay model in which transient Notch signaling from differentiating cells provides a positive template for the onset of differentiation two rows ahead, conveying both temporal and spatial information to propagate oscillations and crystal-like order.

developmental biology↗

bioRxiv2024

A tension-induced morphological transition shapes the avian extra-embryonic territory

The segregation of the extra-embryonic lineage is one of the earliest events and a key step in amniote development. Whereas the regulation of extra-embryonic cell fate specification has been extensively studied, little is known about the morphogenetic events underlying the formation of this lineage. Here, taking advantage of the amenability of avian embryos to live and quantitative imaging, we investigate the cell- and tissue-scale dynamics of epiboly, the process during which the epiblast expands to engulf the entire yolk. We show that tension arising from the outward migration of the epiblast border on the vitelline membrane stretches extra-embryonic cells, which reversibly transition from a columnar to squamous morphology. The propagation of this tension is strongly attenuated in the embryonic territory, which concomitantly undergoes fluid-like motion, culminating in the formation of the primitive streak. We formulate a simple viscoelastic model in which the tissue responds elastically to isotropic stress but flows in response to shear stress, and show that it recapitulates the flows and deformation of both embryonic and extra-embryonic tissues. Together, our results clarify the mechanical basis of early avian embryogenesis and provide a framework unifying the divergent mechanical behaviors observed in the contiguous embryonic and extra-embryonic territories that make up the epiblast. HighlightsO_LIThe extra-embryonic region expands radially during epiboly C_LIO_LICell area increase accounts for the rapid extra-embryonic expansion C_LIO_LIEpiboly-induced tension reversibly stretches extra-embryonic cells C_LIO_LIA simple viscoelastic model recovers the morphogenesis of the entire epiblast C_LI

developmental biology↗

bioRxiv2021

Self-organized tissue mechanics underlie embryonic regulation

Early amniote development is a highly regulative and self-organized process, capable to adapt to interference through cell-cell interactions, which are widely believed to be mediated by molecules. Analyzing intact and mechanically perturbed avian embryos, we show that the mechanical forces that drive embryogenesis self-organize in an analog of Turings molecular reaction-diffusion model, with contractility locally self-activating and the ensuing tension acting as a long-range inhibitor. This mechanical feedback governs the persistent pattern of tissue flows that shape the embryo and steers the concomitant emergence of embryonic territories by modulating gene expression, ensuring the formation of a single embryo under normal conditions, yet allowing the emergence of multiple, well-proportioned embryos upon perturbations. Thus, mechanical forces are a central signal in embryonic self-organization, feeding back onto gene expression to canalize both patterning and morphogenesis.

developmental biology↗

bioRxiv2018

Glutamate spillover in C. elegans triggers repetitive behavior through presynaptic activation of MGL-2/mGluR5

Glutamate is a major excitatory neurotransmitter, and impaired glutamate clearance following synaptic release promotes spillover, inducing extra-synaptic signaling. The effects of glutamate spillover on animal behavior and its neural correlates are poorly understood. We developed a glutamate spillover model in Caenorhabditis elegans by inactivating the conserved glial glutamate transporter GLT-1. GLT-1 loss drives aberrant repetitive locomotory reversal behavior through uncontrolled oscillatory release of glutamate onto AVA, a major interneuron governing reversals. Repetitive glutamate release and reversal behavior require the glutamate receptor MGL-2/mGluR5, expressed in RIM and other interneurons presynaptic to AVA. mgl-2 loss blocks oscillations and repetitive behavior; while RIM activation is sufficient to induce repetitive reversals in glt-1 mutants. Repetitive AVA firing and reversals require EGL-30/Gq, an mGluR5 effector. Our studies reveal that cyclic autocrine presynaptic activation drives repetitive reversals following glutamate spillover. That mammalian GLT1 and mGluR5 are implicated in pathological motor repetition suggests a common mechanism controlling repetitive behaviors.

neuroscience↗

bioRxiv2018

A tensile ring drives tissue flows to shape the gastrulating amniote embryo

Tissue morphogenesis is driven by local cellular deformations, themselves powered by contractile actomyosin networks. While it is well demonstrated that cell-generated forces at the microscopic scale underlie a variety of local morphogenetic processes (e.g. lengthening/ narrowing1-4, bending5-8, or folding9,10), how such local forces are transmitted across tissues to shape them at a mesoscopic scale remains largely unknown. Here, by performing a quantitative analysis of gastrulation in entire avian embryos, we show that the formation of the primitive streak and the associated large-scale rotational tissue flows (i.e. polonaise movements11,12) are integral parts of a global process that is captured by the laws of fluid mechanics. We identify a large-scale supracellular actomyosin ring (2 mm in diameter and 250 m thick) that shapes the embryo by exerting a graded tension along the margin between the embryonic and extra-embryonic territories. Tissue-wide flows arise from the transmission of these localized forces across the embryonic disk and are quantitatively recapitulated by a fluid-mechanical model based on the Stokes equations for viscous flow. We further show that cell division, the main driver of cell rearrangements at this stage13, is required for fluid-like behavior and for the progress of gastrulation movements. Our results demonstrate the power of a hydrodynamic approach to tissue-wide morphogenetic processes14-16 and provide a simple, unified mechanical picture of amniote gastrulation. A tensile embryo margin, in addition to directing tissue motion, could act as an interface between mechanical and molecular cues, and play a central role in embryonic self-organization.

developmental biology↗