Rj. Colello et al., THE CHRONOLOGY OF OLIGODENDROCYTE DIFFERENTIATION IN THE RAT OPTIC-NERVE - EVIDENCE FOR A SIGNALING STEP INITIATING MYELINATION IN THE CNS, The Journal of neuroscience, 15(11), 1995, pp. 7665-7672
In order to determine the signals that initiate axon myelination in th
e CNS, we have chronicled the differentiation of oligodendrocytes in t
he rat optic nerve and related this to the time course and spatial gra
dient seen for optic axon myelination. By using markers specific to th
e varying stages of oligodendrocyte differentiation we found that olig
odendrocyte progenitor cells, present throughout the length of the ner
ve at postnatal day 2, mature into GC+ oligodendrocytes in a chiasm to
eye progression. This gradient along the nerve of oligodendrocyte dif
ferentiation continues with oligodendrocytes near the chiasm expressin
g the genes and encoded proteins to MBP and PLP 3 d before oligodendro
cytes near the eye, Although oligodendrocyte differentiation and matur
ation occurs in a chiasm to eye gradient along the nerve, optic axon s
egments near the eye are ensheathed with myelin before segments near t
he chiasm, This suggests that the myelination of optic axons is initia
ted by a signaling step that is independent of oligodendrocyte differe
ntiation and is stronger near the eye than the chiasm region of the ne
rve, By examining proposed axonal signals, we found that the onset of
myelination is independent of the electrical activity of an axon but c
an be correlated to the size of an axon.