Paralemmin 2 is a shared, alternatively-spliced regulator of axon initial segments and paranodal junctions in oligodendrocytes

Abstract

Nervous system function depends on highly specialized axonal membrane domains. For example, axon initial segments (AIS), nodes of Ranvier, and paranodal junctions are essential for action potential initia-tion and saltatory conduction. These domains use shared molecular machinery converging on the master scaffolding protein AnkyrinG (AnkG). Using endogenous AnkG-TurboID proximity proteomics, we identify Paralemmin 2 (Palm2), a previously uncharacterized CNS protein, as a shared component of the AIS and nodes of Ranvier in neurons, and paranodes in oligodendrocytes. Palm2 localizes transiently to the AIS and nodes during development, but is found at paranodes throughout life, reflecting cell type-specific splicing of a lipid-modified domain both necessary and sufficient for AnkG interaction. Mice lacking oli-godendroglial Palm2 assemble normal paranodes during development, but aged mice lose paranode in-tegrity due to loss of paranodal AnkG and Neurofascin-155. Our findings identify Palm2 as a lipid raft-associated regulator of axonal and oligodendroglial membrane domains and reveal cell type-specific pro-tein variants as a recurring principle for specializing axonal and glial membrane architectures.