Biology subjects

Livet, J.

Publications and source records attributed to Livet, J..

5 recordsLinked to original sources

bioRxiv2025

Tunneling Nanotube-like Connections in the Developing Cerebellum: Distinct from Cytokinetic and Intercellular Bridges

Intercellular communication is essential for brain development. While classical modes--paracrine, juxtacrine, and synaptic signaling--are well characterized, emerging evidence suggests that membranous bridges, such as tunneling nanotubes (TNTs), forming de novo between cells and mainly described in vitro, may also contribute. Yet their presence and function in vivo remain unclear, partly due to the difficulty of distinguishing them from other intercellular connections (ICs). Building on connectomic observations in fixed tissue reporting ICs in the external granule layer (EGL) of the developing cerebellum, we examined their nature in postnatal day 7 (P7) mice. Using immunofluorescence, sparse genetic labelling, and live imaging, we distinguished division-independent ICs from cytokinetic bridges (CBs) and intercellular bridges (IBs). CBs were detected in the EGL, whereas IBs were not observed in this region. In addition to CBs, we identified membranous protrusions which appeared to link clonally and non-clonally related cells. The presence of these ICs reinforces previous connectomic evidence in fixed tissue and raises the possibility that they may participate in intercellular communication during cerebellar development. These findings warrant further investigation into a potentially underexplored mode of communication in the developing brain.

neuroscience↗

bioRxiv2022

Spontaneous and multifaceted ATP release from astrocytes at the scale of hundreds of synapses

Astrocytes participate in information processing by releasing neuroactive substances termed gliotransmitters, including ATP. Individual astrocytes come into contact with thousands of synapses with their ramified structure, but the spatiotemporal dynamics of ATP gliotransmission remain unclear, especially in physiological brain tissue. Using a genetically encoded fluorescent sensor, GRABATP1.0, we discovered that extracellular ATP increased locally and transiently in absence of stimuli in neuron-glia co-cultures, cortical slices, and the anesthetized mouse brain. Spontaneous ATP release events were tetrodotoxin-insensitive but suppressed by gliotoxin, fluorocitrate, and typically spread over 50-250 m2 area at concentrations capable of activating purinergic receptors. Besides, most ATP events did not coincide with Ca2+ transients. Clustering analysis revealed that these events followed multiple distinct kinetics, and blockade of exocytosis only decreased a minor group of slow events. Overall, astrocytes spontaneously release ATP through multiple mechanisms, mainly in non-vesicular and Ca2+-independent manners, thus potentially regulating hundreds of synapses all together.

neuroscience↗

bioRxiv2022

A single cell transcriptomic and clonal analysis depicts valvulogenesis

Congenital heart malformations often include mitral valve defects which remain largely unexplained. During embryogenesis, a restricted population of endocardial cells within the atrioventricular canal (AVC) undergoes endothelial to mesenchymal transition (EndMT) to give rise to mitral valvular cells. However, the identity, fate decisions of these progenitors as well as the distribution of their derivatives in valve leaflets remain unknown. Here, we use scRNA-seq of genetically labeled mouse AVC endocardial cells and of micro-dissected embryonic and postnatal mitral valves to characterize the developmental road. We uncovered the genetic, cell signaling and metabolic processes underlying specification of the progenitors and how they contribute to subtypes of endothelial and interstitial embryonic and postnatal valvular cells. Using clonal genetic tracing with multicolor reporter, we describe specific modes of growth of endocardial cell-derived clones which build up in a proper manner functional valve leaflets. Our data reveal how both genetic and metabolic specification mechanisms specifically drive the fate of a subset of endocardial cells toward valve progenitors and their distinct clonal contribution to the formation of the valve.

developmental biology↗

bioRxiv2020

A scale-space approach for 3D neuronal traces analysis

AO_SCPLOWBSTRACTC_SCPLOWTridimensional microscopy and algorithms for automated segmentation and tracing are revolutionizing neuroscience through the generation of growing libraries of neuron reconstructions. Innovative computational methods are needed to analyze these neural traces. In particular, means to analyse the geometric properties of traced neurites along their trajectory have been lacking. Here, we propose a local tridimensional (3D) scale metric derived from differential geometry, which is the distance in micrometers along which a curve is fully 3D as opposed to being embedded in a 2D plane or 1D line. We apply this metric to various neuronal traces ranging from single neurons to whole brain data. By providing a local readout of the geometric complexity, it offers a new mean of describing and comparing axonal and dendritic arbors from individual neurons or the behavior of axonal projections in different brain regions. This broadly applicable approach termed nAdder is available through the GeNePy3D open-source Python quantitative geometry library.

neuroscience↗

bioRxiv2019

Direct readout of neural stem cell transgenesis with an integration-coupled gene expression switch

SUMMARYStable genomic integration of exogenous transgenes is critical for neurodevelopmental and neural stem cell studies. Despite the emergence of tools driving genomic insertion at high rates with DNA vectors, transgenesis procedures remain fundamentally hindered by the impossibility to distinguish integrated transgenes from residual episomes. Here, we introduce a novel genetic switch termed iOn that triggers gene expression upon insertion in the host genome, enabling simple, rapid and faithful identification of integration events following transfection with naked plasmids accepting large cargoes. In vitro, iOn permits rapid drug-free stable transgenesis of mouse and human pluripotent stem cells with multiple vectors. In vivo, we demonstrate accurate cell lineage tracing, assessment of regulatory elements and mosaic analysis of gene function in somatic transgenesis experiments that reveal new aspects of neural progenitor potentialities and interactions. These results establish iOn as an efficient and widely applicable strategy to report transgenesis and accelerate genetic engineering in cultured systems and model organisms.

developmental biology↗