Biology subjects

Courchet, J.

Publications and source records attributed to Courchet, J..

8 recordsLinked to original sources

bioRxiv2026

Selective vulnerability of intracortical projection neurons drives long-term cortical circuit rewiring after perinatal hypoxia

Cortical circuits are built at perinatal times and gradually refined in an activity-dependent manner during a so-called postnatal period of critical plasticity. Although lesions of the central nervous system (CNS) happening during this period typically recover better than those occurring later in life, they are often associated with long-term behavioral deficits. This suggests that neuronal circuits rewiring, in particular within the cortex, may either be incomplete or inappropriate. To address this possibility, we used chronic perinatal hypoxia, a mouse model of very premature birth. We confirmed that chronic hypoxia induced a decrease in cortical thickness frequently observed in very preterm babies, which rapidly recovered 8 days later. To explore the transcriptional correlates of this recovery we next performed single-nuclei transcriptomic analysis of the cortex at short (P11) and long (P45) timepoints following hypoxia. This revealed persistent transcriptional changes within neurons, including of genes involved in mitochondrial metabolism, axonogenesis and synaptogenesis. Further, histological analysis using anterograde and retrograde tracing as well as mitochondrial labelling support persistent alterations in upper cortical neurons resulting in increased cortico-cortical connectivity within the cortex of adult hypoxic mice. Finally, behavioral testing revealed altered social behavior in mice exposed to chronic hypoxia, which amplified with age. Altogether, our results unravel how brain lesions happening early in life, alter normal cortical development and have long term consequences on cortical wiring, contributing to the observed behaviors defects appearing later in life.

neuroscience↗

bioRxiv2025

The AMPK-related kinase NUAK1 regulates neuronal morphogenesis through the RNA splicing co-factor SON

In recent years, alternative splicing emerged as a major mechanism controlling gene-regulatory networks during brain development, yet how alternative splicing is tuned to the dynamic alterations underlying neuronal maturation remains poorly understood. Here, we identified that NUAK1, an AMPK-related kinase linked to neurodevelopmental disorders, is a key regulator of alternative splicing in developing cortical neurons. Mechanistically, NUAK1 exerts its function through phosphorylation of the splicing co-factor SON, regulating a group of highly conserved splicing events in genes crucial for neurodevelopment. We demonstrate that SON plays an important role in cortical neuron development, which is consistent with the neurodevelopmental phenotypes observed in Zhu-Tokita-Takenouchi-Kim (ZTTK) syndrome, a genetic disorder caused by SON haploinsufficiency. Together, our findings uncover a novel pathway involving NUAK1 and SON, which orchestrate a splicing program required for proper neuronal development.

neuroscience↗

bioRxiv2024

Comparative study of pre- and post-mortem perfusion of fixative for the quality of neuronal tissue preparation

Transcardiac perfusion of fixative agent is generally recommended for quality preparations for cerebral histology, ensuring rapid and deep penetration in the tissue to preserve the most fragile brain structures. Despite being performed under anesthesia and with proper analgesia, this procedure is cumbersome for the experimenter and raises ethical questions. Recently, alternative protocols have been proposed, based on prior sacrifice of the animal followed by an injection of a fixative agent into the circulation. These so-called post-mortem perfusion protocols should in theory ensure an equivalent quality of tissue fixation, without exposing live animals to a procedure. Before adopting this new method, it is necessary to validate that sample quality is equivalent, ensuring the validity of scientific results. We performed a parallel comparison of several protocols of tissue fixation, by transcardiac or post-mortem perfusion, and measured the impact on the maintenance of axonal structures, dendritic spines, and mitochondrial morphology. Our results showed that histological parameters show variable sensitivity to perfusion condition and fixative used. For instance, axon fragmentation and altered mitochondrial morphology were observed in post-mortem perfusion groups. We furthermore determined that fixation condition had a variable effect on immunostaining, impacting detected expression level or pattern. Our results serve as a guide to orient the experimenter in selecting the best condition for optimal tissue fixation, which minimizes animal suffering while guaranteeing the integrity of the biological results obtained.

neuroscience↗

bioRxiv2022

Growth cone macropinocytosis of neurotrophin receptor and neuritogenesis are regulated by Neuron Navigator 1

Neuron Navigator 1 (Nav1) is a cytoskeleton-associated protein expressed during brain development that is necessary for proper neuritogenesis, but the underlying mechanisms are poorly understood. Here we show that Nav1 is present in elongating axon tracts during mouse brain embryogenesis. We found that depletion of Nav1 in cultured neurons disrupts growth cone morphology and neurotrophin-stimulated neuritogenesis. In addition to regulating both F-actin and microtubule properties, Nav1 promotes actin-rich membrane ruffles in the growth cone, and promotes macropinocytosis at those membrane ruffles, including internalization of the TrkB receptor for the neurotrophin BDNF (brain-derived neurotropic factor). Growth cone macropinocytosis is important for downstream signaling, neurite targeting, and membrane recycling, implicating Nav1 in one or more of these processes. Depletion of Nav1 also induces transient membrane blebbing via disruption of signaling in the Rho GTPase signaling pathway, supporting the novel role of Nav1 in dynamic actin-based membrane regulation at the cell periphery. These data demonstrate that Nav1 works at the interface of microtubules, actin, and plasma membrane to organize the cell periphery and promote uptake of growth and guidance cues to facilitate neural morphogenesis during development.

neuroscience↗

bioRxiv2020

ERRα coordinates actin and focal adhesion dynamics

Cell migration depends on the dynamic organization of the actin cytoskeleton and assembly and disassembly of focal adhesions (FA). However the precise mechanisms coordinating these processes remain poorly understood. We previously identified the estrogen-related receptor (ERR) as a major regulator of cell migration. Here, we show that loss of ERR leads to abnormal accumulation of actin filaments that is associated with an increase in the level of inactive form of the actin-depolymerizing factor cofilin. We further show that ERR depletion decreases cell adhesion and promotes defective FA formation and turnover. Interestingly, specific inhibition of the RhoA-ROCK-LIMK-cofilin pathway rescues the actin polymerization defects resulting from ERR silencing, but not cell adhesion. Instead we found that MAP4K4 is a direct target of ERR and down-regulation of its activity rescues cell adhesion and FA formation in the ERR-depleted cells. Altogether, our results highlight a crucial role of ERR in coordinating the dynamic of actin network and focal adhesion through the independent regulation of the RhoA and MAP4K4 pathways.

cell biology↗

bioRxiv2020

The AMPK-related kinase NUAK1 controls cortical axons branching though a local modulation of mitochondrial metabolic functions

The precise regulation of the cellular mechanisms underlying axonal morphogenesis is essential to the formation of functional neuronal networks. We previously identified the autism-candidate kinase NUAK1 as a central regulator of axon branching in mouse cortical neurons through the control of mitochondria trafficking. How does local mitochondrial position or function regulate axon branching during development? Here, we characterized the metabolic regulation in the developing axon and report a marked metabolic decorrelation between axon elongation and collateral branching. We next solved the cascade of event leading to presynaptic clustering and mitochondria recruitment during spontaneous branch formation. Interestingly and contrary to peripheral neurons, mitochondria are recruited after but not prior to branch formation in cortical neurons. Using flux metabolomics and fluorescent biosensors, we observed that NUAK1 deficiency significantly impairs mitochondrial metabolism and axonal ATP concentration. Upregulation of mitochondrial function is sufficient to rescue axonal branching in NUAK1 null neurons in vitro and in vivo. Altogether, our results indicate that NUAK1 exerts a dual function during axon branching through its ability to control mitochondria distribution and activity, and suggest that a mitochondrial-dependent remodeling of local metabolic homeostasis plays a critical role during axon morphogenesis.

neuroscience↗

bioRxiv2019

Muscle MACF1 maintains myonuclei and mitochondria localization through microtubules to control muscle functionalities

Skeletal muscle is made from multinuclear myofiber, where myonuclei are positioned at the periphery or clustered below neuromuscular junctions (NMJs). While mispositioned myonuclei are the hallmark of numerous muscular diseases, the molecular machinery maintaining myonuclei positioning in mature muscle is still unknown. Here, we identified microtubule-associated protein MACF1 as an evolutionary conserved regulator of myonuclei positioning, in vitro and in vivo, controlling the \"microtubule code\" and stabilizing the microtubule dynamics during myofibers maturation, preferentially at NMJs. Specifically, MACF1 governs myonuclei motion, mitochondria positioning and structure and acetylcholine receptors (AChRs) clustering. Macf1-KO in young and adult mice decreases muscle excitability and causes evolutionary myonuclei positioning alterations in adult mice, paralleled with high mitochondria content and improved resistance to fatigue. We present MACF1 as a primary actor of the maintenance of synaptic myonuclei and AChRs clustering, peripheral myonuclei positioning and mitochondria organization through the control of microtubule network dynamics in muscle fibers.

cell biology↗

bioRxiv2018

Haploinsufficiency of autism candidate gene NUAK1 impairs cortical development and behavior

Recently, numerous rare de novo mutations have been identified in children diagnosed with autism spectrum disorders (ASD). However, despite the predicted loss-of-function nature of some of these de novo mutations, the affected individuals are heterozygous carriers, which would suggest that most of these candidate genes are haploinsufficient and/or that these mutations lead to expression of dominant-negative forms of the protein. Here, we tested this hypothesis with the gene Nuak1, recently identified as a candidate ASD gene and that we previously identified for its role in the development of cortical connectivity. We report that Nuak1 is happloinsufficient in mice in regard to its function in cortical axon branching in vitro and in vivo. Nuak1+/- mice show a combination of abnormal behavioral traits ranging from defective memory consolidation in a spatial learning task, defects in social novelty (but not social preference) and abnormal sensorimotor gating and prepulse inhibition of the startle response. Overall, our results demonstrate that Nuak1 haploinsufficiency leads to defects in the development of cortical connectivity and a complex array of behavorial deficits compatible with ASD, intellectual disability and schizophrenia.

neuroscience↗