Biology subjects

Ambiel, N.

Publications and source records attributed to Ambiel, N..

6 recordsLinked to original sources

bioRxiv2026

Actin disassembly triggers CNS myelin compaction and wrapping

Compact myelin enables rapid and precise impulse conduction in the vertebrate nervous system. During CNS development, oligodendrocytes wrap spirally around axons while compacting membranes, yet how cytoskeletal remodeling is coupled to these events remains unclear. Actin disassembly is required for wrapping, but whether wrapping is driven by iterative actin-based protrusion or follows a transition to actin-independent mechanisms is unresolved. Here we integrate tract-resolved developmental profiling, live-cell compaction mapping, and in vivo genetic perturbation to define how actin disassembly is coupled to myelin wrapping. We find that actin filaments undergo pronounced, sustained disassembly before active wrapping begins, with little evidence for persistent actin within sheaths during wrapping. We develop a live-cell assay that maps membrane compaction in cultured oligodendrocytes and show that compaction zones are depleted of actin filaments and expand when actin disassembly is promoted. Consistent with this model, oligodendrocyte-specific actin disassembly in vivo accelerates the appearance of thicker myelin early in development. Together, our results support a model in which actin disassembly promotes myelin wrapping by enabling membrane compaction, and provide a platform to dissect how compaction is regulated in development and disease.

neuroscience↗

bioRxiv2025

RNA switch model for localization and translation of the myelin basic protein mRNA

Oligodendrocytes myelinate the central nervous system by extending cellular projections that ensheath axons and elongate to form lipid-rich myelin. Classic studies visualizing RNA dynamics showed that myelin basic protein (MBP), one of the most abundant myelin proteins, is locally synthesized at the myelin sheath through the transport and local translation of Mbp mRNA. Mbp transport requires its 1.5-kb 3 untranslated region (3 UTR) and prior work identified candidate sub-sequences that may act as cis-acting transport stimulating RNA elements, including one with putative secondary structure. Here, a high-throughput reporter assay, dimethyl sulfate (DMS)-based RNA structure probing, and microscopy in primary rat oligodendrocytes identify a structured 127-nt region that we name the Mbp localization signal (MLS) as both necessary and sufficient for RNA enrichment to oligodendrocyte projections. Lysate pulldown experiments further identify hnRNP-F - a known constituent of the Mbp RNA granule that can suppress mRNA translation - as associated with the MLS; paradoxically, binding of this protein should compete with the ordered MLS RNA structure. These results suggest a model in which the MLS switches between two RNA conformations with distinct protein partners during the transition from Mbp mRNA transport to Mbp translation at the myelin sheath. Such regulation of RNA behavior by structure switching may generalize to other eukaryotic mRNAs whose behaviors shift across space and time. Significance StatementIn the brain, oligodendrocyte cells generate myelin, a type of insulation that wraps around neuronal axons in order to facilitate fast electrical signaling. A critical step in myelination is the local translation of MBP (myelin basic protein) in the myelin sheath. This requires the transport of Mbp mRNA, an incompletely understood phenomenon that we revisit using two recent approaches for mRNA structure and function. We refine a 127-nt region that is necessary and sufficient for mRNA transport to the myelin sheath. A proteomic screen reveals that this myelin localization signal (MLS) associates with a translation-suppressing protein called hnRNP-F, suggesting a model where Mbp mRNA switches between two states, one for transport and one for translation at the myelin sheath.

cell biology↗

bioRxiv2024

Nanobodies against the myelin enzyme CNPase as tools for structural and functional studies

2,3-cyclic nucleotide 3-phosphodiesterase (CNPase) is an abundant constituent of central nervous system non-compact myelin, frequently used as a marker antigen for myelinating cells. The catalytic activity of CNPase, the 3-hydrolysis of 2,3-cyclic nucleotides, is well characterised in vitro, but the in vivo function of CNPase remains unclear. CNPase interacts with the actin cytoskeleton to counteract the developmental closure of cytoplasmic channels that travel through compact myelin; its enzymatic activity may be involved in adenosine metabolism and RNA degradation. We developed a set of high-affinity nanobodies recognizing the phosphodiesterase domain of CNPase, and the crystal structures of each complex show that the five nanobodies have distinct epitopes. One of the nanobodies bound deep into the CNPase active site and acted as an inhibitor. Moreover, the nanobodies were characterised in imaging applications and as intrabodies, expressed in mammalian cells, such as primary oligodendrocytes. Fluorescently labelled nanobodies functioned in imaging of teased nerve fibers and whole brain tissue sections, as well as super-resolution microscopy. These anti-CNPase nanobodies provide new tools for structural and functional biology of myelination, including high-resolution imaging of nerve tissue.

biochemistry↗

bioRxiv2023

Oligodendrocyte calcium signaling regulates myelin sheath morphology

Myelin is essential for rapid nerve signaling and is increasingly found to play important roles in learning and in diverse diseases of the CNS. Morphological parameters of myelin such as sheath length and thickness are regulated by neuronal activity and can precisely tune conduction velocity, but the mechanisms controlling sheath morphology are poorly understood. Local calcium signaling has been observed in nascent myelin sheaths and can be modulated by neuronal activity. However, the role of calcium signaling in sheath formation and remodeling is unknown. Here, we used genetic tools to attenuate oligodendrocyte calcium signaling during active myelination in the developing mouse CNS. Surprisingly, we found that genetic calcium attenuation did not grossly affect the number of myelinated axons or myelin thickness. Instead, calcium attenuation caused striking myelination defects resulting in shorter, dysmorphic sheaths. Mechanistically, calcium attenuation reduced actin filaments in oligodendrocytes, and an intact actin cytoskeleton was necessary and sufficient to achieve accurate myelin morphology. Together, our work reveals a novel cellular mechanism required for accurate CNS myelin formation and provides mechanistic insight into how oligodendrocytes may respond to neuronal activity to sculpt myelin sheaths throughout the nervous system.

neuroscience↗

bioRxiv2022

Schwann cells promote sensory neuron excitability during development

Excitability--the ability to fire action potentials--is a signature feature of neurons. How neurons become excitable during development, and whether excitability is an intrinsic property of neurons or requires signaling from glial cells, remain unclear. Here we demonstrate that Schwann cells, the most abundant glia in the peripheral nervous system, promote somatosensory neuron excitability during development. We find that Schwann cells secrete prostaglandin E2, which is necessary and sufficient to induce developing somatosensory neurons to express normal levels of voltage-gated sodium channels and fire action potential trains. Inactivating this signaling pathway specifically in Schwann cells selectively impairs the maturation of nociceptor and proprioceptor somatosensory neuron subtypes, leading to corresponding sensory defects in thermoception, inflammatory pain, and proprioception. Our studies thus reveal a cell non-autonomous mechanism by which glia regulate neuronal excitability to enable the development of normal sensory functions.

neuroscience↗

bioRxiv2022

SRF transcriptionally regulates the oligodendrocyte cytoskeleton during CNS myelination

Myelination of neuronal axons is essential for nervous system development. Myelination requires dramatic cytoskeletal dynamics in oligodendrocytes, but how actin is regulated during myelination is poorly understood. We recently identified serum response factor (SRF)--a transcription factor known to regulate expression of actin and actin regulators in other cell types--as a critical driver of myelination in the aged brain. Yet, a major gap remains in understanding the fundamental role of SRF in oligodendrocyte lineage cells. Here we show that SRF is required cell autonomously in oligodendrocytes for myelination during development. Combining ChIP-seq with RNA-seq identifies SRF-target genes in OPCs and oligodendrocytes that include actin and other key cytoskeletal genes. Accordingly, SRF knockout oligodendrocytes exhibit dramatically reduced actin filament levels early in differentiation, consistent with its role in actin-dependent myelin sheath initiation. Together, our findings identify SRF as a transcriptional regulator that controls the expression of cytoskeletal genes required in oligodendrocytes for myelination. This study identifies a novel pathway regulating oligodendrocyte biology with high relevance to brain development, aging, and disease. HighlightsO_LIDevelopmental CNS myelination requires the transcription factor SRF in oligodendrocytes. C_LIO_LISRF targets actin and actin-regulatory but not myelin related genes. C_LIO_LISRF drives oligodendrocyte actin cytoskeleton dynamics during early stages of myelination. C_LI

neuroscience↗