Selective and compartmentalized myelin expression of HspB5

Abstract

In the present study, we reveal myelin-specific expression and targeting of mRNA and biochemical pools of HspB5 in the mouse CNS. Our observations are based on in situ hybridization, electron microscopy and co-localization with 2',3'-Cyclic-Nucleotide 3'-Phosphodiesterase (CNPase), reinforcing this myelin-selective expression. HspB5 mRNA might be targeted to these structures based on its presence in discrete clusters resembling RNA granules and the presence of a putative RNA transport signal. Further, sub-cellular fractionation of myelin membranes reveals a distinct sub-compartment-specific association and detergent solubility of HspB5. This is akin to other abundant myelin proteins and is consistent with HspB5's association with cytoskeletal/membrane assemblies. Oligodendrocytes have a pivotal role in supporting axonal function via generating and segregating the ensheathing myelin. This specialization places extreme structural and metabolic demands on this glial cell type. Our observations place HspB5 in oligodendrocytes which may require selective and specific chaperone capabilities to maintain normal function and neuronal support.

The transcriptome of mouse central nervous system myelin

“…The rapidly increased abundance of CRYAB upon a neuroinflammatory challenge protects myelin and neurons from degeneration 37 . By in situ -hybridization, Cryab -mRNA in oligodendrocytes localized away from the cell bodies 38 , in resemblance of Mbp -mRNA 24 . Indeed, Cryab -mRNA is enriched in myelin according to the present analysis.…”

A myelinic channel system for motor-driven organelle transport

“…Indeed, normal myelin sheath growth requires nucleation of microtubules, that is mediated by tubulin polymerization promoting protein (TPPP) (Fu et al, 2019; Lehotzky et al, 2010; Tokési et al, 2010). Further, mRNAs encoding myelin proteins and presumably the oligodendroglial translation machinery is transported on microtubules to the tip of the growing sheath (Brophy et al, 1993; Carson et al, 1998; Colman et al, 1982; Holz et al, 1996; Kursula et al, 2001; Quraishe et al, 2016; Trapp et al, 1987).…”

Identifying mRNAs Residing in Myelinating Oligodendrocyte Processes as a Basis for Understanding Internode Autonomy

“…(1) high expression by neurons (KIF1A, MAPK8IP1 and DYNC1LI2 mRNAs) or ependymal cells (APOD mRNA); (2) expression levels which are too low to determine with the RT-qPCR protocol used (DYNC1LI2 and PADI2 mRNAs); or (3) exclusion from myelin (ENPP2 and NDRG1 mRNAs) resulting from the use of hypertonic sucrose for homogenization. As ISH studies clearly show that CAR2 [15], CRYAB [16], MATP [73] and KIF1A [17] mRNAs reside in MSAS, either in cultured oligodendrocytes and/or tissues, ISH studies could be used to find out whether or not mRNAs of interest reside in MSAS (Section 4.4.1).…”

“…Complementing screening protocols, ISH could confirm mRNAs that co-localize with MBP mRNA in MSAS. Published studies have used ISH to show that alternatively-spliced isoforms of myelin-associated oligodendrocytic basic protein (MOBP) [12], highly basic proteins that co-reside with MBP Life 2023, 13, 945 2 of 26 in the mammalian CNS myelin major dense line [13], alternatively-spliced isoforms of microtubule associated protein tau (MAPT) [14], carbonic anhydrase 2 (CAR2) [15], αBcrystallin (CRYAB) [16], and kinesin family member 1A (KIF1A) [17].…”

“…Six MSAS mRNAs were enriched in myelin over levels in starting material used for subcellular fractionation as determined by Northern blot (++). References to mRNAs experimentally linked to oligodendrocyte differentiation and/or myelination are: (1) APOD [21,22], (2) ENPP2 [23,24], (3) GSN [25,26], (4) LPAR1 [27], ( 5) NDRG1 [28][29][30][31], ( 6) PADI2 [32][33][34][35][36], (7) TPPP [37][38][39], (8) CAR2 [15,40], (9) CRYAB [16,41].…”