Biology subjects

Bin, J. M.

Publications and source records attributed to Bin, J. M..

5 recordsLinked to original sources

bioRxiv2026

Fatty acid binding protein-8 (FABP8/PMP2) reveals molecular heterogeneity of myelin sheaths in the human CNS

Myelin is classically viewed as a uniform axon-insulating membrane, yet its molecular composition may differ between species and even within one species. Fatty acid binding protein-8 (FABP8/PMP2) was previously identified in CNS myelin of humans but not mice. Here we show that FABP8/PMP2 is a defining feature of CNS myelin in humans and old-world-monkeys, but absent from CNS myelin in other mammals, indicating evolutionary neofunctionalization of this lipid-binding protein in the primate lineage. In the human CNS, FABP8/PMP2 marks a subset of myelin sheaths that preferentially ensheath large-diameter axons, revealing sheath-to-sheath molecular heterogeneity correlated with axonal geometry. Chromatin is accessible at the PMP2/Pmp2 gene locus in oligodendrocytes of humans but not mice. Human oligodendrocytes intrinsically express FABP8/PMP2 when transplanted into mouse brains, demonstrating species-specific competence independent of environmental cues. Humanized transgenic mice expressing FABP8/PMP2 in oligodendrocytes form morphologically normal but developmentally transiently thicker myelin sheaths, and show elevated cholesterol content in purified myelin. Because FABP8/PMP2 binds cholesterol, we propose that its emergence in primate CNS myelin contributes to the cholesterol enrichment of human myelin. Thus, CNS myelin protein composition is evolvable and modular, with relevance for myelin lipids and morphology, and previously unrecognized complexity in neuron-glia co-adaptation. Main points- Fatty acid binding protein 8 (FABP8/PMP2) is present in CNS myelin of humans and old-world monkeys - PMP2 defines sheath-to-sheath heterogeneity in the human CNS - PMP2-immunopositive myelin ensheaths large-diameter axons - Human oligodendrocytes intrinsically express PMP2 upon transplantation into mice - Humanized PMP2-transgenic mice show thicker myelin and altered myelin lipid composition

neuroscience↗

bioRxiv2025

High-resolution phenotypic screen in zebrafish identifies novel regulators of CNS axon diameter growth

Axon diameter varies up to 100-fold between distinct neurons in the central nervous system with larger axons exhibiting proportionally faster conduction velocity. Axon diameter influences myelination, can be dynamically regulated, which might help fine-tune neural circuit function, and is altered in several diseases. Despite its importance, mechanisms regulating axon diameter remain poorly understood. This gap in understanding is due in part to the limitations of fixed tissue analyses, such as electron microscopy, which cannot be scaled up to execute discovery screens. To address this, we developed a high-resolution, high-content imaging-based in vivo platform to identify pharmacological modulators of axon diameter in zebrafish. We focused on the Mauthner neuron, whose axon diameter growth can be monitored during development. To facilitate our high-content chemical screen, we developed an automated high-resolution imaging and image analysis pipeline to assess changes in Mauthner axon diameter in transgenic reporter animals. We screened 880 compounds and identified 33 that altered Mauthner axon diameter. Validating this discovery pipeline, we confirmed that compounds that affect beta-2 adrenoceptor and dopamine signaling increase axon diameter in separate follow-up studies. This represents the first discovery screen for axon diameter regulators, providing novel entry points to study the biology of axon diameter regulation.

neuroscience↗

bioRxiv2025

Developmental axon diameter growth of central nervous system axons does not depend on ensheathment or myelination by oligodendrocytes

Myelination facilitates the rapid conduction of action potentials along axons. In the central nervous system (CNS), myelinated axons vary over 100-fold in diameter, with conduction speed scaling linearly with increasing diameter. Axon diameter and myelination are closely interlinked, with axon diameter exerting a strong influence on myelination. Conversely, myelinating Schwann cells in the peripheral nervous system can both positively and negatively affect axon diameter. However, whether axon diameter is regulated by CNS oligodendrocytes is less clear. Here, we investigated CNS axon diameter growth in the absence of myelin using mouse (Mbpshi/shi and Myrf conditional knockout) and zebrafish (olig2 morpholino) models. We find that neither the ensheathment of axons, nor the formation of compact myelin are required for CNS axons to achieve appropriate and diverse diameters. This indicates that developmental CNS axon diameter growth is independent of myelination, and shows that myelinating cells of CNS and PNS differentially influence axonal morphology.

neuroscience↗

bioRxiv2023

Importin 13-dependent Axon Diameter Growth Regulates Conduction Speeds along Myelinated CNS Axons

Central nervous system neurons have axons that vary over 100-fold in diameter. This diversity contributes to the regulation of myelination and conduction velocity along axons, which is critical for proper nervous system function. Despite this importance, technical challenges have limited our understanding of mechanisms controlling axon diameter growth, preventing systematic dissection of how manipulating diameter affects conduction along individual axons. Here, we establish zebrafish as system to investigate the regulation of axon diameter and axonal conduction in vivo. We identify a role for importin 13b specifically in axon diameter growth, that is independent of axonal length and overall cell size. Impairment of diameter growth along individual myelinated axons reduced conduction velocity in proportion to the diameter, but had no effect on the precision of action potential propagation or ability to fire at high frequencies. This work highlights an axon diameter-specific mechanism of growth that regulates conduction speeds along myelinated axons.

neuroscience↗

bioRxiv2020

Paranode stability requires UNC5B expression by oligodendrocytes

In the mature CNS, netrin-1 is expressed by neurons and oligodendrocytes and implicated in the stability of axo-oligodendroglial paranodal junctions. Here we report that the netrin receptor UNC5B is highly expressed by mature oligodendrocytes and enriched at paranodes. We demonstrate that paranodes become disorganized following conditional deletion of UNC5B in oligodendrocytes, with disruption of the interface between glial loops and detachment of loops from the axon. As a result, Caspr1 and Kv1.1 disperse along the axon, internodes fail to lengthen and compact myelin periodicity is reduced. Paranodal and axoglial domain disorganization progressively worsens and a delay in motor learning develops in aged mice lacking oligodendroglial UNC5B. Altered glial loop ultrastructure and reduced levels of claudin-11 and JAM-C tight junction proteins support the conclusion that disruption of autotypic junctions between paranodal loops underlies paranode disorganization. Our findings reveal an essential contribution of oligodendroglial UNC5B at paranodes that is required for the stability of mature myelin.

neuroscience↗