Biology subjects

Marshall-Phelps, K. L.

Publications and source records attributed to Marshall-Phelps, K. L..

3 recordsLinked to original sources

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↗

bioRxiv2019

TET1-mediated DNA hydroxy-methylation regulates adult remyelination

Adult myelination is essential for brain function and response to injury, but the molecular mechanisms remain elusive. Here we identify DNA hydroxy-methylation, an epigenetic mark catalyzed by Ten-Eleven translocation (TET) enzymes, as necessary for adult myelin repair. While DNA hydroxy-methylation and high levels of TET1 are detected in young adult mice during myelin regeneration after demyelination, this process is defective in old mice. Constitutive or inducible lineage-specific ablation of Tet1 (but not of Tet2) recapitulate the age-related decline of DNA hydroxy-methylation and inefficient remyelination. Genome-wide hydroxy-methylation and transcriptomic analysis identify numerous TET1 targets, including several members of the solute carrier (Slc) gene family. Lower transcripts for Slc genes, including Slc12a2, are observed in Tet1 mutants and old mice and are associated with swelling at the neuroglial interface, a phenotype detected also in zebrafish slc12a2b mutants. We conclude that TET1-mediated DNA hydroxy-methylation is necessary for adult remyelination after injury.

neuroscience↗

bioRxiv2019

Disruption to NKCC1 impairs the response of myelinating Schwann cells to neuronal activity and leads to severe peripheral nerve pathology

Myelinating Schwann cells of the peripheral nervous system (PNS) express numerous ion channels and transporters, and have the capacity to respond to neuronal activity. However, it remains unknown how the response of Schwann cells to neuronal activity affects peripheral nerve formation, health or function in vivo. Through a genetic screen in zebrafish, we identified a mutant, ue58, with severe disruption to the morphology of myelin along peripheral nerves and associated nerve oedema. Molecular analyses indicated that this phenotype was caused by the loss of function of a previously uncharacterized gene, slc12a2b, which encodes a zebrafish paralog of the solute carrier NKCC1. NKCC1 is a co-transporter of Na+, K+, and Cl- ions and water, typically from the extracellular space into cells. Upon impairing slc12a2b function, constitutively, or specifically in neurons or myelinating Schwann cells, we observed disruption to myelin and nerve oedema. Strikingly, we found that treatment of slc12a2b mutants with TTX completely prevented the emergence of these pathologies. Furthermore, TTX treatment rescued pathology in animals with cell-type specific loss of slc12a2b from myelinating Schwann cells. Together our data indicate that NKCC1 regulates ion homeostasis following neuronal activity and that this is required to maintain myelinated axon and peripheral nerve integrity.

neuroscience↗