Journal of Neuroscience, Vol 2, 986-993, Copyright © 1982 by Society for Neuroscience
Myelin formation in rotation-mediated aggregating cell cultures: immunocytochemical, electron microscopic, and biochemical observations
BD Trapp, HD Webster, D Johnson, RH Quarles, SR Cohen and MR Murray
Myelination was studied in aggregating cell cultures derived from
mechanically 15- to 16-day fetal rat brains. Myelin basic protein (MBP) and
myelin-associated glycoprotein (MAG) were localized immunocytochemically in
20-micrometers-thick Vibratome and 1-micrometer- thick Epon sections at 15,
20, 25, and 30 days in vitro. The occurrence of these proteins was
correlated with the ultrastructural appearance of oligodendrocytes and
myelin sheaths and with biochemical levels of MBP, MAG, and the
myelin-related enzyme, 2',3'-cyclic nucleotide 3'- phosphodiesterase (CNP).
MBP appeared in ultrastructurally immature oligodendrocyte cytoplasm at 15
days in vitro. As oligodendrocytes developed a more differentiated fine
structure, MBP and MAG antisera stained oligodendrocyte processes and
myelin sheaths. Immunostaining in Vibratome sections demonstrated that MBP
was detectable in oligodendrocytes and myelin prior to MAG. At 25 days in
vitro, all Vibratome sections contained MBP- and MAG-stained
oligodendrocytes and myelin sheaths. Radioimmunoassays for MBP and MAG and
enzyme assays for CNP in whole homogenates of the aggregates revealed that
each of these components increased with the progression of myelination.
However, MBP only reached 8% of the level in adult rat brain, while MAG and
CNP increased to more than half of the adult level. The protein composition
of myelin purified from 30-day aggregates resembled that of myelin purified
from immature rat brain.