Expression of genes for the myelin-specific proteins in oligodendrocytes in vivo demands the presence of axons.

The level and distribution of mRNAs for several myelin-specific proteins were analyzed by in situ hybridization histochemistry in the mouse optic nerves after severance by eye enucleation during the period of active myelination, viz. the 2nd postnatal week. The autoradiographic signals for 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP)-, myelin basic protein (MBP)- and myelin-associated glycoprotein (MAG)-mRNAs all decreased progressively in the postoperative time course and all the signals fell below the detectable level by the 7th postoperative day. These findings indicate that the levels of genes for all the three major myelin-specific proteins in oligodendrocytes in vivo are down-regulated at the transcriptional level after axonal withdrawal.