Biology subjects

Lefebvre, J. L.

Publications and source records attributed to Lefebvre, J. L..

5 recordsLinked to original sources

bioRxiv2026

TRACR: an anterograde transneuronal tracing system for genetic access across synapses and longitudinal circuit analysis

Following neural signals as they converge onto and diverge from individual neurons is central to understanding circuit function and disease-related dysfunction. Existing anterograde transneuronal tracers are limited by cytotoxicity and incomplete genetic control over connected partners. To address these limitations, we adapted synthetic Notch designs to create TRanssynaptic Anterograde Circuit Readout (TRACR). Binding of the engineered ligand-receptor across synapses induces TRE-driven reporter transcription, enabling characterization of postsynaptic neurons. TRACR provides segregated genetic access to pre- and postsynaptic populations, and can be combined with markers, sensors, or effectors to expand circuit analysis. By applying TRACR at multiple synapses in the mouse visual system, we show that TRACR labels postsynaptic partners of sensory neurons, long-range projections and local inhibitory interneurons. TRACR signaling is reversible and fails to activate when synapses are absent or disrupted. Together, TRACR is an accessible, AAV-deliverable transneuronal reporting tool for longitudinal analysis of circuit assembly, degeneration, and repair. HIGHLIGHTSO_LITRACR adapts the synNotch system to signal across synapses for tracing postsynaptic targets. C_LIO_LITRACR identifies local and long-range postsynaptic targets in the mouse visual system. C_LIO_LITRACR activation requires intact synaptic connectivity rather than proximity. C_LIO_LITRACR signals are reversible, diminishing upon synapse loss and activating following assembly. C_LI

neuroscience↗

bioRxiv2022

Gamma-Protocadherins regulate filopodia self-recognition and dynamics to drivedendrite self-avoidance

Neurons form cell type-specific morphologies that are shaped by molecular cues and their cellular events governing dendrite growth. One growth rule is distributing dendrites uniformly within a neurons territory by avoiding sibling or self branches. In mammalian neurons, dendrite self-avoidance is regulated by the clustered Protocadherins (cPcdhs), a large family of recognition molecules. Genetic and molecular studies suggest that the cPcdhs mediate homophilic recognition and repulsion between self-dendrites but this model has not been tested through direct investigation of self-avoidance during development. Here we performed live imaging and 4D quantifications of dendrite morphogenesis to define the cPcdh-dependent mechanisms of self-avoidance. We focused on the mouse retinal starburst amacrine cell (SAC), which requires the gamma-Pcdhs (Pcdhgs) and self/non-self recognition to establish a stereotypic radial morphology while permitting dendritic interactions with neighboring SACs. Through morphogenesis, SACs extend a transient population of dynamic filopodia that fill the growing arbor and contact nearby self-dendrites. Compared to non-self-contacting filopodia, self-contacting events have longer lifetimes and a subset persists as filopodia bridges. In the absence of the Pcdhgs, non-self-contacting filopodia dynamics are unaffected but self-contact-induced retractions are significantly diminished. Filopodia bridges accumulate, leading to the bundling of dendritic processes and disruption to the arbor shape. By tracking dendrite self-avoidance in real-time, our findings demonstrate that the {gamma}-Pcdhs selectively mediate contact-induced retractions upon filopodia self-recognition. Our results also illustrate how self-avoidance shapes the stochastic and space-filling behaviors of filopodia for robust dendritic pattern formation in mammalian neurons. HIGHLIGHTSO_LIDendrite self-avoidance proceeds through interstitial filopodia and contact-induced retractions between sibling processes. C_LIO_LISelf-contacting filopodia exhibit longer lifetimes and a subset of contacts persist. C_LIO_LIPcdhgs selectively regulate self-contact-induced retractions. C_LIO_LILoss of Pcdhgs and filopodia self-avoidance disrupts dendritic arbor shape. C_LI

neuroscience↗

bioRxiv2022

γ-Protocadherins control synapse formation and peripheral branching of touch sensory neurons

Light touch sensation begins with activation of low-threshold mechanoreceptor (LTMR) endings in the skin and propagation of their signals to the spinal cord and brainstem. We found that the clustered protocadherin gamma (Pcdhg) gene locus, which encodes 22 cell-surface homophilic binding proteins, is required in somatosensory neurons for normal behavioral reactivity to a range of tactile stimuli. Developmentally, distinct Pcdhg isoforms mediate LTMR synapse formation through neuron-neuron interactions and peripheral axonal branching through neuron-glia interactions. The Pcdhgc3 isoform mediates homophilic interactions between sensory axons and spinal cord neurons to promote synapse formation in vivo, and is sufficient to induce postsynaptic specializations in vitro. Moreover, loss of Pcdhgs and somatosensory synaptic inputs to the dorsal horn lead to fewer corticospinal synapses onto dorsal horn neurons. These findings reveal essential roles for Pcdhg isoform diversity in somatosensory neuron synapse formation, peripheral axonal branching, and step-wise assembly of central mechanosensory circuitry.

neuroscience↗

bioRxiv2020

Morphological pseudotime ordering and fate mapping reveals diversification of cerebellar inhibitory interneurons

Understanding how diverse neurons are assembled into circuits requires a framework for describing cell types and their developmental trajectories. Here, we combined genetic fate mapping and pseudo-temporal profiling to resolve the diversification of cerebellar inhibitory interneurons based on morphology. The molecular layer interneurons (MLIs) derive from a common progenitor but comprise a diverse population of dendritic-, somatic-, and axon initial segment-targeting interneurons. MLIs are classically divided into two types. However, their morphological heterogeneity suggests an alternate model of one continuously varying population. Through clustering and trajectory inference of 811 MLI reconstructions at maturity and during development, we show that MLIs divide into two discrete classes but also present significant within-class heterogeneity. Pseudotime trajectory mapping uncovered the emergence of distinct phenotypes during migration and axonogenesis, well before neurons reach their final positions. Our study illustrates the utility of quantitative single-cell methods to morphology for defining the diversification of neuronal subtypes.

neuroscience↗

bioRxiv2020

The gamma-Protocadherins regulate the survival of GABAergic interneurons during developmentally-regulated cell death.

Inhibitory interneurons integrate into developing circuits in specific ratios and distributions. In the cortex, the formation of inhibitory networks occurs concurrently with the apoptotic elimination of a third of GABAergic interneurons. The molecular mechanisms that select GABAergic interneurons to survive or die are unknown. Here we report that the clustered Protocadherins regulate GABAergic cell survival in the developing brain. Deletion of the Pcdh-gamma genes (Pcdhgs) from GABAergic neurons in mice causes a severe loss of inhibitory neurons in multiple brain regions and results in motor deficits and seizure activities. By focusing on the neocortex and cerebellar cortex, we demonstrate that GABAergic interneuron loss results from elevated apoptosis during the postnatal wave of Bax-dependent programmed cell death. Pro-survival AKT signals are reduced in Pcdhg-deficient interneurons, diminishing the intrinsic capacity of interneurons to compete and incorporate into developing networks. We propose that the Pcdhgs mediate selective GABAergic interneuron survival to contribute to the formation of balanced inhibitory networks.

neuroscience↗