Biology subjects

Bardet, P.-L.

Publications and source records attributed to Bardet, P.-L..

7 recordsLinked to original sources

bioRxiv2026

Spinal lumen remodeling under the control of Gli signaling mechanically drives roof plate cells extension

Morphogenesis often requires different cell types to coordinate their behaviors for an harmonious developpement. How these different cell type behaviors are synchronized within and between tissues remains one of the important questions to fully understand morphogenesis. We used the zebrafish developing spinal cord to study this question. At later stages of neurogenesis, the lumen of the neural tube remodels, by reducing its height dramatically to form the persisting ventral central canal, a morphogenetic process conserved in vertebrates. By combining genetics, cell signaling manipulation with antagonist drugs and high-resolution in vivo live imaging, we better characterised the dynamics and control of this remodeling process. We showed that the lumen retraction depends on Gli activity regulation, a downstream effector of the Shh morphogen signal. We further established that the lumen retraction is instrumental in the cellular elongation of spinal roof plate cells, a population that forms the ceiling of the spinal cord lumen. Our work therefore establishes that the Gli transcriptional regulators under the control of long-range morphogen Shh control lumen retraction and that this retraction is a key driver of the roof plate cells extension.

developmental biology↗

bioRxiv2025

Dynamic interactions between epithelial skin cells and a sensory cavity sculpt the growing olfactory orifice

During morphogenesis and in pathological conditions, gaps can form in the plane of epithelial barriers upon cellular forces that disrupt intercellular junctions. How the size of these epithelial holes further increases over time and what sets their shape remain poorly understood. Here we analyze the formation of the olfactory orifice (the nostril) in zebrafish, which opens and grows in the skin epithelium above a rosette of olfactory placode cells, allowing the sensory neurons to directly access odor cues. Using quantitative imaging and tissue-specific perturbations, we analyzed the dynamic remodeling of skin cells allowing the expansion of the orifice edge. We identified the sensory cavity located in the center of the placodal rosette as a crucial player that sets the size of the growing epithelial hole in the skin. We further showed that fine-tuning of actomyosin contractility within each tissue (skin and sensory cavity) exerts non-autonomous effects on the neighboring tissue, thereby shaping the nostril structure. This study uncovers dynamic cell behaviors and reciprocal tissue-tissue interplay that control the growth and shape of an epithelial hole in vivo.

developmental biology↗

bioRxiv2024

ASTROGLIOSIS AND NEUROINFLAMMATION UNDERLIE SCOLIOSIS UPON CILIA DYSFUNCTION

Cilia defects lead to scoliosis in zebrafish, but the underlying pathogenic mechanisms are poorly understood and may diverge depending on the mutated gene. Here, we dissected the mechanisms of scoliosis onset in a zebrafish mutant for the rpgrip1l gene encoding a ciliary transition zone protein. rpgrip1l mutant fish developed scoliosis with near-total penetrance but asynchronous onset in juveniles. Taking advantage of this asynchrony, we found that curvature onset was preceded by ventricle dilations and was concomitant to the perturbation of Reissner fiber polymerization and to the loss of multiciliated tufts around the subcommissural organ. Rescue experiments showed that Rpgrip1l was exclusively required in foxj1a-expressing cells to prevent axis curvature. Genetic interactions investigations ruled out Urp1/2 levels as a main driver of scoliosis in rpgrip1 mutants. Transcriptomic and proteomic studies identified neuroinflammation associated with increased Annexin levels as a potential mechanism of scoliosis development in rpgrip1l juveniles. Investigating the cell types associated with annexin2 over-expression, we uncovered astrogliosis, arising in glial cells surrounding the diencephalic and rhombencephalic ventricles just before scoliosis onset and increasing with time in severity. Anti-inflammatory drug treatment reduced scoliosis penetrance and severity and this correlated with reduced astrogliosis and macrophage/microglia enrichment around the diencephalic ventricle. Mutation of the cep290 gene encoding another transition zone protein also associated astrogliosis with scoliosis. Thus, we propose astrogliosis induced by perturbed ventricular homeostasis and associated with immune cell activation as a novel pathogenic mechanism of zebrafish scoliosis caused by cilia dysfunction.

developmental biology↗

bioRxiv2020

Adrenergic activation modulates the signal from the Reissner fiber to cerebrospinal fluid-contacting neurons during development

The cerebrospinal fluid (CSF) contains an extracellular thread that is conserved in vertebrates and referred to as the Reissner fiber. Genetic ablation in the zebrafish revealed that the Reissner fiber controls body axis morphogenesis in the embryo. Yet, the signaling cascade originating from this fiber to ensure body axis straightening is not fully understood. Here, we explore the functional link between the Reissner fiber and undifferentiated spinal neurons contacting the CSF (CSF-cNs). First, we show that the Reissner fiber is required for the expression of urp2, a neuropeptide expressed in CSF-cNs. Using in vivo calcium imaging, we show that the Reissner fiber is also required for embryonic calcium transients in these spinal neurons. Finally, we study how local adrenergic activation directly in the CSF can substitute for the Reissner fiber-signaling pathway to CSF-cNs and rescue body axis morphogenesis. Our results suggest that the Reissner fiber acts on CSF-cNs to establish body axis morphogensis by controlling the availability of a chemical signal in the CSF.

developmental biology↗

bioRxiv2019

Sensory neurons contacting the cerebrospinal fluid require the Reissner fiber to detect spinal curvature in vivo

Recent evidence indicate active roles for the cerebrospinal fluid (CSF) on body axis development and morphogenesis of the spine implying CSF-contacting neurons (CSF-cNs) in the spinal cord. CSF-cNs project a ciliated apical extension into the central canal that is enriched in the channel PKD2L1 and enables the detection of spinal curvature in a directional manner. Dorsolateral CSF-cNs ipsilaterally respond to lateral bending while ventral CSF-cNs respond to longitudinal bending. Historically, the implication of the Reissner fiber (RF), a long extracellular thread in the CSF, to CSF-cN sensory functions has remained a subject of debate. Here, we reveal using electron microscopy in zebrafish larvae that the RF is in close vicinity with cilia and microvilli of ventral and dorsolateral CSF-cNs. We investigate in vivo the role of cilia and the Reissner fiber in the mechanosensory functions of CSF-cNs by combining calcium imaging with patch-clamp recordings. We show that disruption of cilia motility affects CSF-cN sensory responses to passive and active curvature of the spinal cord without affecting the Pkd2l1 channel activity. Since ciliary defects alter the formation of the Reissner fiber, we investigated whether the Reissner fiber contributes to CSF-cN mechanosensitivity in vivo. Using a hypomorphic mutation in the scospondin gene that forbids the aggregation of SCO-spondin into a fiber, we demonstrate in vivo that the Reissner fiber per se is critical for CSF-cN mechanosensory function. Our study uncovers that neurons contacting the cerebrospinal fluid functionally interact with the Reissner fiber to detect spinal curvature in the vertebrate spinal cord. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=152 SRC="FIGDIR/small/861344v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@3c7baaorg.highwire.dtl.DTLVardef@db094forg.highwire.dtl.DTLVardef@4041c6org.highwire.dtl.DTLVardef@9e3dae_HPS_FORMAT_FIGEXP M_FIG C_FIG eToCThe role of the Reissner fiber, a long extracellular thread running in the cerebrospinal fluid (CSF), has been since its discovery in 1860 a subject of debate. Orts-DelImmagine et al. report that the Reissner fiber plays a critical role in the detection of spinal curvature by sensory neurons contacting the CSF. HighlightsO_LISince its discovery, the role of the Reissner fiber has long been a subject of debate C_LIO_LIMechanoreception in CSF-contacting neurons (CSF-cNs) in vivo requires the Reissner fiber C_LIO_LICSF-cN apical extension is in close vicinity of the Reissner fiber C_LIO_LICSF-cNs and the Reissner fiber form in vivo a sensory organ detecting spinal curvature C_LI

neuroscience↗

bioRxiv2019

Origin of bidirectionality of cerebrospinal fluid flow and impact on long-range transport between brain and spinal cord

The circulation of cerebrospinal fluid (CSF) plays pivotal roles for body axis formation and brain development. During embryogenesis, CSF is rich in particles and proteins and flows bidirectionally in the central canal. The origins of bidirectional flow and its impact on development are unknown. Experiments combined with modeling and simulations demonstrate that the bidirectionality of CSF flow is generated locally by caudally-polarized motile cilia confined to the ventral wall of the central canal. Such active bidirectional flow of the CSF accelerates the long-range transport of particles propagating rostrally and caudally. In addition, spontaneous muscle contractions increase local CSF flow and consequently enhance long-range transport of extracellular lipidic particles. Focal ablation of the channel connecting brain ventricles to the central canal reduces embryo length, indicating that long-range transport contributes to embryonic growth. Our study also demonstrates that at this early stage, motile cilia ensure the proper formation of the central canal.

biophysics↗

bioRxiv2018

Pkd2l1 is required for mechanoception in cerebrospinal fluid-contacting neurons and maintenance of spine curvature

Flow of cerebrospinal fluid (CSF) may contribute to spine morphogenesis, as mutations affecting both cilia motility and CSF flow lead to scoliosis1. However, the mechanisms underlying detection of the CSF flow in the central canal of the spinal cord remain elusive. Here we used full-field optical coherence tomography (FF-OCT) and bead tracking to demonstrate that CSF flows bidirectionally along the antero-posterior axis in the central canal of zebrafish embryos. In the zebrafish mutant cfap298tm304, previously known as kurly, reduction of cilia motility slows transport down the length of central canal. To investigate downstream mechanisms that could transduce CSF flow, we performed calcium imaging in sensory neurons contacting the CSF (CSF-cNs) and found that disruption in cilia motility impaired the activity of CSF-cNs. CSF-cNs across species express the transient receptor potential channel PKD2L1, also known as TRPP3, which contributes to CSF-cN chemosensory properties. Using calcium imaging and whole-cell patch clamp recordings, we found that the loss of the Pkd2l1 channel in pkd2l1 mutant embryos also abolished CSF-cN activity. Whole-cell recordings further demonstrated that opening of a single channel is sufficient to trigger action potentials in wild type CSF-cNs. Recording from isolated cells in vitro, we showed that CSF-cNs are mechanosensory cells that respond to pressure in a Pkd2l1-dependent manner. Interestingly, adult pkd2l1 mutant zebrafish develop an exaggerated spine curvature, reminiscent of kyphosis in humans. Our study indicates that CSF-cNs are mechanosensory cells whose spontaneous activity reflects CSF flow in vivo. Furthermore, Pkd2l1 in CSF-cNs contributes to the maintenance of the natural curvature of the spine.

neuroscience↗