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Myelin basic protein deficit in the PNS of mld mutant mice recovers during development
Abstract:
Myelination was studied between 15 and 135 days postnatally in peripheral nerves of myelin deficient (mld) mice and in unaffected littermates. The nerve weights were not affected by the mutation and showed a 4-fold increase during the developmental period studied. The amounts of myelin present in peripheral nerves, as shown by biochemical and morphological techniques, were slightly reduced in mld in comparison to control mice. In controls, the concentration of myelin doubled during the investigation period. The increase of myelin basic protein (MBP) in total nerve homogenate paralleled the deposition of myelin, but the MBP concentration remained constant in normal myelin. In contrast, in mld myelin MBP concentrations were extremely low until 60 days of age and increased thereafter to reach almost normal values at 135 days. Similarly, the amounts of myelin isolated at 85 and 135 days were normal. 2',3'-Cyclic nucleotide 3'-phosphodiesterase (CNP; EC 3.1.4.37), the myelin-specific enzyme, showed normal specific activities in mld nerves. In mld and control myelin, CNP-specific activities decreased during development suggesting a preferential localization of CNP in Schwann cell plasma membranes. In contrast to the central nervous system, other myelin proteins were not altered in mld peripheral nervous system (PNS) and the very low MBP content had no severe repercussions on the composition and structure of the myelin sheath. Furthermore, Schwann cells appeared normal in mld PNS. Nevertheless, more subtle alterations could be detected. Slightly decreased amounts of myelin were observed in young mld mice and preliminary results indicate discrete alterations of the myelin periodicity.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Myelin basic protein (MBP) levels were low in young myelin deficient (mld) mice but recovered by adulthood. Peripheral nerve myelination showed subtle alterations, not severe repercussions, in mld mice compared to controls.
Area of Science:
- Neuroscience
- Developmental Biology
- Biochemistry
Background:
- Myelination is crucial for peripheral nerve function.
- The myelin deficient (mld) mouse model offers insights into myelination defects.
- Understanding myelin composition and protein dynamics is key to neurological health.
Purpose of the Study:
- To investigate myelination and myelin composition in the peripheral nervous system (PNS) of mld mice.
- To compare myelin basic protein (MBP) levels and enzyme activity in mld and control mice during development.
- To assess the impact of the mld mutation on PNS myelin structure and Schwann cells.
Main Methods:
- Biochemical and morphological analysis of peripheral nerves from mld and control mice (15-135 days postnatal).
- Quantification of myelin content and myelin basic protein (MBP) concentrations.
- Assay of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) activity.
Main Results:
- Peripheral nerve weights increased similarly in mld and control mice.
- Slightly reduced myelin amounts were observed in young mld mice, with MBP levels recovering by adulthood.
- Myelin-specific enzyme CNP showed normal activity, suggesting normal Schwann cell function despite subtle myelin alterations.
Conclusions:
- The mld mutation causes mild alterations in PNS myelination, with significant recovery of MBP levels by adulthood.
- Unlike the central nervous system, the mld mutation has limited impact on PNS myelin composition and structure.
- Schwann cells appear largely unaffected, indicating robust compensatory mechanisms in the PNS.