Immunolocalization of 17 and 21.5 kDa MBP isoforms in compact myelin and radial component

Area of Science:

• Neuroscience
• Biochemistry
• Cell Biology

Background:

• Biochemical analyses indicated elevated levels of minor myelin basic protein (MBP) isoforms (21.5 and 17 kDa) in CNS myelin enriched in interlamellar junctions.
• The precise localization of these minor MBP isoforms within the myelin sheath remained to be substantiated.

Purpose of the Study:

• To determine the specific localization of 21.5 and 17 kDa MBP isoforms within the myelin sheath using immunoelectron microscopy.
• To differentiate the distribution of minor MBP isoforms from major MBP isoforms in murine CNS myelin.

Main Methods:

• Immunoelectron microscopy on thin-sections of mouse optic nerve.
• Utilized two distinct polyclonal antibodies: Ab-MBP21.5 (specific to 21.5 and 17 kDa MBP) and Ab-MBP14 (reactive to all four MBP isoforms).
• SDS-PAGE and immunoblotting to confirm antibody specificity.

Main Results:

• Ab-MBP21.5 specifically recognized only the 21.5 and 17 kDa MBP isoforms, while Ab-MBP14 recognized all MBP isoforms.
• Ab-MBP14 showed significantly higher binding to junction-free compact myelin compared to the radial component.
• Ab-MBP21.5 exhibited similar binding to both junction-free compact myelin and the radial component.
• Within junction-free compact myelin, both antibodies demonstrated preferential binding to the major dense line over the intraperiod line.

Conclusions:

• The minor MBP isoforms (21.5 and 17 kDa) are not uniformly distributed within the myelin sheath.
• These minor MBP isoforms show a distinct localization pattern compared to the major MBP isoforms, particularly in relation to myelin structural components like junctions and dense lines.
• Findings provide crucial insights into the structural organization and functional specialization of the myelin sheath.