Biology subjects

Pichaud, F.

Publications and source records attributed to Pichaud, F..

8 recordsLinked to original sources

bioRxiv2025

A Natural Programmable Metamaterial Controls 3D Curvature of Compound Eyes

The panoramic vision of the convex compound eyes, common to insects and crustaceans, relies on micrometer-scale curvature variations1. These variations create specialized visual zones adapted to specific tasks, including detecting prey, mates, or predators2,3. However, the mechanisms by which such fine-scale curvature is encoded during development remain unknown. Here we show that the developing eye of Drosophila melanogaster functions as a natural metamaterial that programs the organs precise 3D curvature. We discover a supracellular triangular mesh in the basal retina with a specific pattern of triangles sizes. Computational simulations demonstrate its role directing the small scale curvature variations of the eye. Genetic disruption of this micropattern prevents local curvature establishment. Furthermore, the presence of a homologous mesh-curvature relationship in Drosophila mauritiana indicates evolutionary conservation of this mechanism. These results reveal a novel mechanism of morphogenesis control in which the supracellular 2D patterning give rise to a biological programmable metamaterial that encodes 3D curvature with great precision4. Our in vivo finding offers a novel framework for the design of shape-programmable 3D biological surfaces with broad implications from synthetic morphogenesis to clinical applications.

developmental biology↗

bioRxiv2024

Super-Resolution Simplified: Sub-10nm Imaging Over Large Areas and Deep Penetration via SDC-OPR and DNA-PAINT

Single Molecule Localization Microscopy (SMLM) has traditionally faced challenges to optimize signal-to-noise ratio, penetration depth, field-of-view (FOV), and spatial resolution simultaneously. Here, we show that DNA-PAINT imaging on a Spinning Disk Confocal with Optical Photon Reassignment (SDC-OPR) system overcomes these trade-offs, enabling high-resolution imaging across multiple cellular layers and large FOVs. We demonstrate the systems capability with DNA origami constructs and biological samples, including nuclear pore complexes, mitochondria, and microtubules, achieving a spatial resolution of 6 nm in the basal plane and sub-10 nm localization precision at depths of 9 {micro}m within a 53 x 53 {micro}m{superscript 2} FOV. Additionally, imaging of the developing Drosophila eye epithelium at depths up to 9 {micro}m with sub-13 nm average localization precision, reveals distinct E-cadherin populations in adherens junctions. Quantitative analysis of Collagen IV deposition in this epithelium indicated an average of 46 {+/-} 27 molecules per secretory vesicle. These results underscore the versatility of DNA-PAINT on an SDC-OPR for advancing super-resolution imaging in complex biological systems.

biophysics↗

bioRxiv2022

A Dystroglycan-Laminin-Integrin axis controls cell basal geometry remodeling in the developing Drosophila retina

Cell shape remodeling is a principal driver of epithelial tissue morphogenesis. While progress continues to be made in our understanding of the pathways that control the apical (top) geometry of epithelial cells, we know comparatively little about those that control cell basal (bottom) geometry. To examine this issue, we used the fly ommatidium, which is the basic visual unit of the compound eye. The ommatidium is shaped as a hexagonal prism, and generating this three-dimensional structure requires ommatidial cells to adopt specific apical and basal polygonal geometries. Using this model system, we find that generating cell type-specific basal geometries starts with patterning of the basement membrane, whereby Laminin accumulates at discrete locations across the basal surface of the retina. We show that the Dystroglycan surface receptor promotes this localized Laminin accumulation. Moreover, our results reveal that localized accumulation of Laminin-Dystroglycan induces polarization of Integrin adhesion in ommatidial cells. This underpins cell basal geometry remodeling by anchoring the basal surface of cells to the basement membrane at specific, discrete locations. Altogether, our work shows that patterning of a basement membrane by generating discrete Laminin domains, can direct Integrin adhesion. In the retina, this pathway generates specific basal polygonal geometries to organize a complex multicellular structure in three-dimensions.

developmental biology↗

bioRxiv2022

RanBP1 plays an essential role in directed migration of neural crest cells during development.

Collective cell migration is essential for embryonic development, tissue regeneration and repair, and has been implicated in pathological conditions such as cancer metastasis. It is, in part, directed by external cues that promote front-to-rear polarity in individual cells. However, our understanding of the pathways that underpin the directional movement of cells in response to external cues remains incomplete. To examine this issue we made use of neural crest cells (NC), which migrate as a collective during development to generate vital structures including bones and cartilage. Using a candidate approach, we found an essential role for Ran-binding protein 1 (RanBP1), a key effector of the nucleocytoplasmic transport pathway, in enabling directed migration of these cells. Our results indicate that RanBP1 is required for establishing front-to-rear polarity, so that NCs are able to chemotax. Moreover, our work suggests that RanBP1 function in chemotaxis involves the polarity kinase LKB1/PAR4. We envisage that regulated nuclear export of LKB1 through Ran/RanBP1 is a key regulatory step required for establishing front-to-rear polarity and thus chemotaxis, during NC collective migration.

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↗

bioRxiv2019

Cell-type specific mechanical response and actomyosin dynamics in the developing Drosophila retina

During organogenesis, different cell types need to work together to induce functional multicellular structures. To study this process, we made use of the genetically tractable fly retina, with a focus on the mechanisms that coordinate morphogenesis between the different epithelial cell types that make up the optical lens. Our work shows that these epithelial cells present contractile apical-medial MyosinII meshworks, which control the apical area and junctional geometry of these cells during lens development. Our study also suggests that MyosinII meshworks drive cell shape changes in response to external forces, and thus they mediate part of the biomechanical coupling that takes place between these cells. Importantly, our work, including mathematical modelling of forces and material stiffness during lens development, raises the possibility that increased cell stiffness acts as a mechanism for limiting this mechanical coupling. We propose this might be required in complex tissues, where different cell types undergo concurrent morphogenesis and where averaging out of forces across cells could compromise individual cell apical geometry and thereby organ function.

developmental biology↗

bioRxiv2019

Cdc42 promotes epithelial morphogenesis by coupling Par-complex and Crumbs recruitment via Par6-aPKC

Epithelial morphogenesis depends on Cdc42, which acts in part through the Par-complex (Baz/Par3-Par6-aPKC), and Crumbs (Crb/CRB3). However, how these proteins come together and interact during morphogenesis is not well understood. Here we show that in Drosophila cells, Cdc42 is active at the apical membrane and cell-cell contacts, and couples apical recruitment of Par6-aPKC and Crb to promote apical identify. This coupling depends on Cdc42 and aPKC binding to Par6, and is mediated by Par6 binding to Crb. Conversely, Crb promotes the apical retention of Par6-aPKC, and thus Cdc42-Par6-aPKC and Crb promote each others apical accumulation to specify the apical membrane and Zonula Adherens (ZA). Altogether, our work shows that epithelial morphogenesis relies on a two tiered-mechanism whereby Cdc42 coordinates Par-complex assembly and apical recruitment of Crb through Par6-aPKC.

cell biology↗

bioRxiv2017

Rap1, AF6 and Pak4 cooperate with Par3 to promote ZA assembly and remodeling in the fly photoreceptor

The epithelial Zonula adherens (ZA) is a main adhesion compartment that enables organogenesis by allowing epithelial cells to assemble into sheets. How ZA assembly is regulated during epithelial cell morphogenesis is not fully understood. We show that during ZA morphogenesis, the function of the small GTPase Rap1 and the F-actin binding protein AF6/Cno are both linked to that of the P21-activated kinase Pak4/Mbt. We find that Rap1 and Mbt regulate each others localization at the ZA and cooperate in promoting ECadherin stabilization. During this process Cno regulates the recruitment of Baz at the ZA, a process that is also regulated by Arm phosphorylation by Mbt. Altogether, we propose that Rap1, Cno and Mbt regulate ZA morphogenesis by coordinating ECadherin stabilization and Baz recruitment and retention. In addition, our work uncovers a new link between two main oncogenes, Rap1 and Pak4/Mbt, in a model developing epithelial cell.

cell biology↗