Biology subjects

Schweisguth, F.

Publications and source records attributed to Schweisguth, F..

8 recordsLinked to original sources

bioRxiv2026

Positional cues, not Notch, direct Neuroblast selection during early neurogenesis in the Drosophila embryo

Notch-mediated lateral inhibition is a conserved patterning process that controls alternative cell fate decisions and produces regular cell fate patterns. Prevailing models posit that lateral inhibition singles-out cells from fields of initially equipotent cells by amplifying stochastic fluctuations of Notch or pre-existing fate biases. Here, we revisited the role of Notch in early Drosophila neurogenesis, studying the dynamics of Neuroblast specification by live imaging the transcription of two proneural genes, scute and lethal of scute. We found that proneural gene expression is biased spatially along the dorsal-ventral axis prior to germ band extension and that early proneural expression predicts Neuroblast fate acquisition. This indicated that Neuroblast specification is pre-patterned by positional cues. Additionally, positional cues appeared to instruct individual cells to delaminate in a correct stereotyped pattern in proneural mutant embryos. Finally, contrary to current models, Notch signaling, measured by E(spl)m8 expression, was not detectable within proneural clusters until after Neuroblasts had initiated delamination. This indicated that Notch functions to stabilize rather than initiate fate decisions. We therefore propose that positional cues, not Notch, single-out Neuroblasts during early Drosophila neurogenesis, challenging long-held assumptions about the role of Notch in Neuroblast selection.

developmental biology↗

bioRxiv2026

EpiCure (Epithelial Curation): a versatile and handy tool for curation of epithelial segmentation

Investigating single-cell dynamics and morphology in tissues and embryos requires highly accurate quantitative analysis of microscopy images. Despite significant advances in the field of bioimage analysis, even the most sophisticated segmentation and tracking algorithms inevitably produce errors (e.g. : over segmentation, missing objects, miss-connected objects). Although error rate may be small, their propagation throughout a time-lapse sequence has catastrophic effects on the accuracy of tracking and extraction of single cell parameters. Extracting single cell temporal information in the context of tissue/embryo requires thus expert curation to identify and correct segmentation errors. In the movies commonly used in developmental biology and stem cell research, both the number of imaged cells and the duration of recording are large, making this manual correction task extremely time-consuming. This has now become a major bottleneck in the fields of development, stem cell biology and bioimage analysis. We present here EpiCure (Epithelial Curation), a versatile tool designed to streamline and accelerate manual curation of segmentation and tracking in 2D movies of large epithelial tissues. EpiCure uses temporal information and morphometric parameters to automatically identify segmentation and tracking errors and provides user-friendly tools to correct them. It focuses on ergonomics and offers several visualization options to help navigating in movies of tissue covering a large number of cells, speeding up the detection of errors and their curation. EpiCure is highly interoperable and supports input from a wide range of segmentation tools. It also includes multiple export filters, enabling seamless integration with downstream analysis pipelines. In this paper, using movies from several animal models, we highlight the importance of curating cell segmentation and tracking for accurate downstream analysis, and demonstrate how EpiCure helps the curation process for extracting accurate single cell dynamics and cellular events detection, making it faster and amenable on large dataset.

developmental biology↗

bioRxiv2026

Oscillatory Hedgehog signaling and temporal coordination of atonal dynamics at the eye differentiation front in Drosophila

Pattern formation in the Drosophila eye involves the pulsatile expression of the proneural gene atonal (ato) and the periodic activation of Notch. Oscillatory expression of the ato gene results from the synchronous activation of two distinct ato enhancers that are active in two adjacent rows of cell clusters along the front of differentiation. How synchronous enhancer activation is achieved along the front is not known. Hedgehog (Hh) is a diffusive signal produced just posterior to the front which contributes to regulate ato gene expression. Here, we find that both ato enhancers are regulated by Hh and that two Hh target genes, patched (ptc) and decapentaplegic (dpp), are expressed at the front of differentiation in an oscillatory manner downstream of a constant Hh signal. Consistent with a role of Hh in the temporal coordination of ato gene expression along the front, lowering Hh activity was associated with pattern irregularities along the front. We propose a model whereby the periodic expression of the Hh receptor Ptc under the control of pulsatile Ato and/or Notch dynamics produces rhythmic changes in extracellular Hh which would in turn coordinate ato dynamics locally. In this model, oscillatory Hh would provide a temporal cue to coordinate patterning dynamics along the front of differentiation in the developing eye.

developmental biology↗

bioRxiv2025

Cellular NAD+ availability and redox state constrain developmental speed in the Drosophila eye

The cellular and biochemical processes that limit the speed at which embryos develop, tissues form, and cells differentiate remain largely unknown. Using the speed of progression of a differentiation front in the developing eye of Drosophila as a proxy for developmental speed, we identified genetic perturbations that slowed down the progression of this front. Inhibiting the Electron Transport Chain (ETC), and more generally energy production in mitochondria, resulted in reduced developmental speed. Defective ETC activity led to increased NADH/NAD+ ratio whereas ATP levels remained constant due to a compensatory increase in glycolysis. Using targeted perturbations, we found that the metabolic state of the cells ahead of and/or at the moving front of differentiation determined its speed. Genetic and diet-based perturbations of the NAD+ metabolism pathway indicated that developmental speed was limited by NAD+ availability in these cells. Thus, developmental speed appeared to be constrained by the cellular redox and the demand for NAD+ in Drosophila.

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↗

bioRxiv2020

Neuralized regulates a travelling wave of Epithelium-to-Neural Stem Cell morphogenesis in Drosophila

Many tissues are produced during development by specialized progenitor cells emanating from epithelia via an Epithelial-to-Mesenchymal Transition (EMT). Most studies have so far focused on cases involving single or isolated groups of cells. Here we describe an EMT-like process that requires tissue level coordination. This EMT-like process occurs along a continuous front in the Drosophila optic lobe neuroepithelium to produce neural stem cells (NSCs). We find that emerging NSCs remain epithelial and apically constrict before dividing asymmetrically to produce neurons. Apical constriction is associated with contractile myosin pulses and requires the E3 ubiquitin ligase Neuralized and RhoGEF3. Neuralized down-regulates the apical protein Crumbs via its interaction with Stardust. Disrupting the regulation of Crumbs by Neuralized led to defects in apical constriction and junctional myosin accumulation, and to imprecision in the integration of emerging NSCs into the transition front. Neuralized therefore appears to mechanically couple NSC fate acquisition with cell-cell rearrangement to promote smooth progression of the differentiation front.

developmental biology↗

bioRxiv2019

Optogenetic inhibition of Delta reveals digital Notch signaling output during tissue differentiation

Spatio-temporal regulation of signalling pathways plays a key role in generating diverse responses during the development of multicellular organisms. The role of signal dynamics in transferring signalling information in vivo is incompletely understood. Here we employ genome engineering in Drosophila melanogaster to generate a functional optogenetic allele of the Notch ligand Delta (opto-Delta), which replaces both copies of the endogenous wild type locus. Using clonal analysis, we show that optogenetic activation blocks Notch activation through cis-inhibition in signal-receiving cells. Signal perturbation in combination with quantitative analysis of a live transcriptional reporter of Notch pathway activity reveals differential tissue- and cell-scale regulatory modes. While at the tissue-level the duration of Notch signalling determines the probability with which a cellular response will occur, in individual cells Notch activation acts through a switch-like mechanism. Thus, time confers regulatory properties to Notch signalling that exhibit integrative digital behaviours during tissue differentiation.

developmental biology↗

bioRxiv2019

Neph/Nephrin-like adhesion and tissue level pulling forces regulate cell intercalation during Drosophila retina development.

Intercalation between neighboring cells contributes to shaping epithelial tissues and is regulated by the contractile actomyosin cytoskeleton. While intercalation typically occurs over minutes, instances of much slower cell intercalation have been reported during organogenesis. This is observed, for example, for the four glial-like cone cells (CC) that intercalate during Drosophila retinal patterning. Here we show that Myosin-II activity in the CCs is largely dispensable for their intercalation. Instead, we find that differential activity of the Notch-signaling pathway within the CC quartet regulates intercalation, which also depends on the cell adhesion proteins Roughest and Hibris. In addition, mathematical modeling predicts that forces external to the intercalating CC quartet are necessary for intercalation. Consistent with this prediction we show that the surrounding primary pigment cells are under significant contractile tension. Altogether, our work elucidates a novel mode of cell intercalation that relies on Neph/Nephrin-like adhesion and forces external to the intercalating cells.

developmental biology↗