Protein 4.1B Localizes on Unmyelinated Axonal Membranes in the Mouse Enteric Nervous System

Recent molecular studies on anchoring structures between myelin sheaths by glial cells (oligodendrocytes and Schwann cells (Sc) in the central (CNS) and peripheral nervous system (PNS), respectively) and axons indicated protein-protein interaction for the polarization of paranodes in the axons. The protein 4.1 (4.1) family was originally found in erythrocytes as a component of membrane skeletons, and genetic approaches revealed the precise family members. One of them, 4.1B, has been reported to be localized in paranodes and juxtaparanodes of myelinated axons. In this study, in addition to the myelinated axons, we also present the localization of 4.1B in nerve fibers in the adult mouse enteric nervous system, a subpopulation of mature unmyelinated nerve fibers in PNS. Ultrastructurally, 4.1B localized along the membranes of unmyelinated axons. Such unmyelinated axons were surrounded only by Sc, suggesting that the 4.1B may also have a role in direct Sc-axon interactions and maturation of the axons, as well as myelinating glial cell-axon interactions.