Expression of QKI proteins and MAP1B identifies actively myelinating oligodendrocytes in adult rat brain.

We have studied developing oligodendrocytes in tissue sections as they initiate myelination and have found that the transition from premyelinating oligodendrocytes into myelin-bearing cells is accompanied by a dramatic upregulation in expression of the RNA binding QKI proteins. We show that in mature oligodendrocytes in culture, the localization of cytoplasmic QKI isoforms requires an intact cytoskeleton. Together with previous observations, this indicates that cytoplasmic QKI proteins facilitate movement of mRNAs to myelin via the cytoskeleton. In the adult rat brain, we found that a subset of oligodendrocytes displays characteristics of actively myelinating cells seen during development, i.e., connections to myelin sheaths and elevated levels of QKI proteins and also MAP1B. These observations suggest that instead of merely maintaining myelin, oligodendrocytes in the normal adult CNS are capable of responding to demands for new myelin sheaths. This has important implications for the prospect of repair of myelin in demyelinating conditions such as multiple sclerosis.