Proteome Profile of Myelin in the Zebrafish Brain

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.

Insights Into Central Nervous System Glial Cell Formation and Function From Zebrafish

“…Myelination by Oligodendrocytes. Similar to other vertebrates, zebrafish oligodendrocytes make multiple myelin sheaths on many axons upon differentiation (Figure 3), and although some differences in components have been noted the overall molecular composition and ultrastructural nature of myelin in zebrafish and mammals appears broadly similar (Jahn et al, 2009(Jahn et al, , 2020Czopka and Lyons, 2011;Preston and Macklin, 2015;Czopka, 2016;Siems et al, 2021) (Figure 3). By live imaging of oligodendrocytes in zebrafish over time using transgenic reporters, Czopka et al (2013) found that individual cells initiate formation of essentially all of their sheaths within a matter of hours following the initiation of the first sheath, pointing to a restricted period in which oligodendrocytes have to select axons for myelination.…”

Cd59 and inflammation orchestrate Schwann cell development

“…For this reason, the genetic mechanisms that orchestrate myelinating glial cell development requires continued exploration. Over the past few decades, we and others have noted expression of cd59 that is conserved in developing myelinating glial cells across multiple organisms, including zebrafish, rodents, and humans (Gerber et al, 2021;Howard et al, 2021;Marisca et al, 2020;Marques et al, 2018Marques et al, , 2016Piller et al, 2021;Saunders et al, 2019;Siems et al, 2021;Sun et al, 2013;Wolbert et al, 2020;Zajicek, 1995;Zhu et al, 2019). Despite these observations, there had been little exploration into the function of Cd59 in the developing nervous system.…”

“…Artwork created by Ashtyn T. Wiltbank with Illustrator (Adobe) based on previous schematics and electron micrographs published in (Ackerman and Monk, 2016;Cunningham and Monk, 2018;Jessen and Mirsky, 2005). features in several RNA sequencing (RNAseq) and proteomic analyses of zebrafish and rodent myelinating glial cells (Gerber et al, 2021;Howard et al, 2021;Marisca et al, 2020;Marques et al, 2018Marques et al, , 2016Piller et al, 2021;Saunders et al, 2019;Siems et al, 2021;Wolbert et al, 2020;Zhu et al, 2019), all of which demonstrate high expression of cd59 in developing oligodendrocyte lineage cells (OLCs) and SCs. cd59 continues to be expressed in juvenile and adult zebrafish (Saunders et al, 2019;Siems et al, 2021;Sun et al, 2013) and becomes the 4 th most abundant CNS myelin protein in adult zebrafish (Siems et al, 2021).…”

“…cd59 continues to be expressed in juvenile and adult zebrafish (Saunders et al, 2019;Siems et al, 2021;Sun et al, 2013) and becomes the 4 th most abundant CNS myelin protein in adult zebrafish (Siems et al, 2021). Phylogenetic analysis demonstrates that Cd59 is conserved within vertebrate evolution (Siems et al, 2021), and accordingly, CD59 protein is also found in developing and adult human myelin (Erne et al, 2002;Koski et al, 2002;Scolding et al, 1998;Zajicek, 1995). Collectively, this data indicates that cd59 is a key component of the genetic program that orchestrates myelinating glial cell development.…”

Conservation and divergence of myelin proteome and oligodendrocyte transcriptome profiles between humans and mice

“…Already early gel-based comparisons between CNS myelin fractions purified from various fish and tetrapod species revealed that the clades comprise overlapping but divergent sets of major myelin proteins 8, 12 . More recently, this finding was extended to low-abundant constituents when quantitative mass spectrometry allowed comparing the CNS myelin proteome between zebrafish and mice 13 . By quantitative proteome analysis, MBP is highly abundant in CNS myelin of either species.…”