Proteome Profile of Myelin in the Zebrafish Brain.

Sophie B Siems,Ramona B Jung,Tim Czopka,Hauke B Werner,Olaf Jahn,Dörte Hesse,Laura J Hoodless,Wiebke Möbius

doi:10.3389/fcell.2021.640169

Abstract

The velocity of nerve conduction along vertebrate axons depends on their ensheathment with myelin. Myelin membranes comprise specialized proteins well characterized in mice. Much less is known about the protein composition of myelin in non-mammalian species. Here, we assess the proteome of myelin biochemically purified from the brains of adult zebrafish (Danio rerio), considering its increasing popularity as model organism for myelin biology. Combining gel-based and gel-free proteomic approaches, we identified > 1,000 proteins in purified zebrafish myelin, including all known constituents. By mass spectrometric quantification, the predominant Ig-CAM myelin protein zero (MPZ/P0), myelin basic protein (MBP), and the short-chain dehydrogenase 36K constitute 12%, 8%, and 6% of the total myelin protein, respectively. Comparison with previously established mRNA-abundance profiles shows that expression of many myelin-related transcripts coincides with the maturation of zebrafish oligodendrocytes. Zebrafish myelin comprises several proteins that are not present in mice, including 36K, CLDNK, and ZWI. However, a surprisingly large number of ortholog proteins is present in myelin of both species, indicating partial evolutionary preservation of its constituents. Yet, the relative abundance of CNS myelin proteins can differ markedly as exemplified by the complement inhibitor CD59 that constitutes 5% of the total zebrafish myelin protein but is a low-abundant myelin component in mice. Using novel transgenic reporter constructs and cryo-immuno electron microscopy, we confirm the incorporation of CD59 into myelin sheaths. These data provide the first proteome resource of zebrafish CNS myelin and demonstrate both similarities and heterogeneity of myelin composition between teleost fish and rodents.

Highlights

Myelination of vertebrate axons accelerates nerve conduction by facilitating saltatory impulse propagation (Tasaki, 1939; Hartline and Colman, 2007)
Upon protein staining using Coomassie Blue or other staining dyes, myelin purified from the brains of mammalian, avian, or reptilian species displayed only four to five bands (Zanetta et al, 1977; Quarles et al, 1978; Franz et al, 1981; Jeserich, 1983), which we know represent one or several splice isoforms each of the transmembrane-tetraspan proteolipid protein (PLP), the cytosolic adhesion protein myelin basic protein (MBP), and the enzyme cyclic nucleotide phosphodiesterase (CNP, previously termed Wolfgram protein)
We have used gel-based and gel-free proteomic approaches to investigate the protein composition of myelin purified from the brains and optic nerves of adult zebrafish

Summary

INTRODUCTION

Myelination of vertebrate axons accelerates nerve conduction by facilitating saltatory impulse propagation (Tasaki, 1939; Hartline and Colman, 2007). Protein staining using Coomassie Brilliant Blue (CBB250) upon separation of myelin on contemporary gradient gels yields numerous distinct bands (Morris et al, 2004; Avila et al, 2007; De MonasterioSchrader et al, 2012), the major constituents of which can be identified by mass spectrometric methods This strategy allowed identification of several constituents of zebrafish myelin, i.e., of the 36K protein as a short-chain dehydrogenase/reductase [36K, termed DHRS12 (Morris et al, 2004)], Zwilling proteins (ZWIa and ZWIb) (Schaefer and Brösamle, 2009), and two MBP paralogs [MBPa, MBPb (Nawaz et al, 2013)]. We assessed CNS myelin purified from adult zebrafish by proteome analysis using a combination of gel-based and gel-free proteomic approaches

MATERIALS AND METHODS

DISCUSSION

Findings

DATA AVAILABILITY STATEMENT