BetaII-Spectrin Gaps and Patches Emerge from the Patterned Assembly of the Actin/Spectrin Membrane Skeleton in Human Motor Neuron Axons

Gazal, N. G.; Castellanos-Montiel, M. J.; Bruno, G.; Franco-Flores, A. K.; Lepine, S.; Gursu, L.; Haghi, G.; Maussion, G.; Anastasia, A.; Bisbal, M.; Gorostiza, E. A.; Durcan, T. M.; Unsain, N.

doi:10.1101/2025.05.09.653215

bioRxiv · 10.1101/2025.05.09.653215

BetaII-Spectrin Gaps and Patches Emerge from the Patterned Assembly of the Actin/Spectrin Membrane Skeleton in Human Motor Neuron Axons

Gazal, N. G.·Castellanos-Montiel, M. J.·Bruno, G.·Franco-Flores, A. K.·Lepine, S.·Gursu, L.·Haghi, G.·Maussion, G.·Anastasia, A.·Bisbal, M.·Gorostiza, E. A.·Durcan, T. M.·Unsain, N.

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Abstract

The actin/spectrin membrane-associated periodic skeleton (MPS) is a cytoskeletal structure that supports axonal integrity and function. Lower spinal motor neurons (MNs) are characterized by exceptionally long axons and are particularly susceptible to degeneration in a wide range of hereditary neuromuscular disorders, including amyotrophic lateral sclerosis. Using confocal and super-resolution imaging, we characterized the spatial distribution {beta}II-spectrin and the assembly pattern of the MPS in human MN axons derived from induced pluripotent stem cells (iPSCs). We discovered a striking gap-and-patch pattern in the medial axon, where sharply demarcated {beta}II-spectrin gaps alternate with patches containing a well-organized MPS. The pattern is acutely induced by the kinase inhibitor staurosporine and pharmacological inhibition of actin polymerization prevents patch formation, indicating a requirement for actin nucleation in MPS assembly. Our data supports a model in which spectrin incorporation into nascent MPS patches depletes neighboring regions, producing long-range gaps-and-patches patterns.

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Gazal, N. G., Castellanos-Montiel, M. J., Bruno, G., Franco-Flores, A. K., Lepine, S., Gursu, L., Haghi, G., Maussion, G., Anastasia, A., Bisbal, M., Gorostiza, E. A., Durcan, T. M., Unsain, N.. 2025-05-12. BetaII-Spectrin Gaps and Patches Emerge from the Patterned Assembly of the Actin/Spectrin Membrane Skeleton in Human Motor Neuron Axons. https://doi.org/10.1101/2025.05.09.653215

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