title: Peripheral axons of the adult zebrafish maxillary barbel extensively remyelinate during sensory appendage regeneration.
abstract: Myelination is a cellular adaptation allowing rapid conduction along axons. We have investigated peripheral axons of the zebrafish maxillary barbel (ZMB), an optically clear sensory appendage. Each barbel carries taste buds, solitary chemosensory cells, and epithelial nerve endings, all of which regenerate after amputation (LeClair and Topczewski [2010] PLoS One 5:e8737). The ZMB contains axons from the facial nerve; however, myelination within the barbel itself has not been established. Transcripts of myelin basic protein (mbp) are expressed in normal and regenerating adult barbels, indicating activity in both maintenance and repair. Myelin was confirmed in situ by using toluidine blue, an anti-MBP antibody, and transmission electron microscopy (TEM). The adult ZMB contains ∼180 small-diameter axons (<2 μm), approximately 60% of which are myelinated. Developmental myelination was observed via whole-mount immunohistochemistry 4-6 weeks postfertilization, showing myelin sheaths lagging behind growing axons. Early-regenerating axons (10 days postsurgery), having no or few myelin layers, were disorganized within a fibroblast-rich collagenous scar. Twenty-eight days postsurgery, barbel axons had grown out several millimeters and were organized with compact myelin sheaths. Fiber types and axon areas were similar between normal and regenerated tissue; within 4 weeks, regenerating axons restored ∼85% of normal myelin thickness. Regenerating barbels express multiple promyelinating transcription factors (sox10, oct6 = pou3f1; krox20a/b = egr2a/b) typical of Schwann cells. These observations extend our understanding of the zebrafish peripheral nervous system within a little-studied sensory appendage. The accessible ZMB provides a novel context for studying axon regeneration, Schwann cell migration, and remyelination in a model vertebrate.
authors.affiliation: Department of Biological Sciences, DePaul University, Chicago, Illinois 60614, USA.
authors.forename: Alex C
authors.initials: AC
authors.lastname: Moore
authors.forename: Tiffany E
authors.initials: TE
authors.lastname: Mark
authors.forename: Ann K
authors.initials: AK
authors.lastname: Hogan
authors.forename: Jacek
authors.initials: J
authors.lastname: Topczewski
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: LeClair
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology* / Q000648:ultrastructure; D051767:Early Growth Response Protein 2 / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology*; D007814:Larva; D046529:Microscopy, Electron, Transmission; D004676:Myelin Basic Protein / Q000235:genetics / Q000378:metabolism*; D009416:Nerve Regeneration / Q000502:physiology*; D050816:Octamer Transcription Factor-6 / Q000235:genetics / Q000378:metabolism; D059348:Peripheral Nerve Injuries / Q000378:metabolism* / Q000503:physiopathology*; D055757:SOXE Transcription Factors / Q000235:genetics / Q000378:metabolism; D012583:Schwann Cells / Q000378:metabolism / Q000648:ultrastructure; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D051767:Early Growth Response Protein 2; D004676:Myelin Basic Protein; D055757:SOXE Transcription Factors; D029961:Zebrafish Proteins; C442229:sox10 protein, zebrafish; D050816:Octamer Transcription Factor-6