DOES OLIGODENDROCYTE SURVIVAL DEPEND ON AXONS

Background: We have shown previously that oligodendrocytes and their p recursors require signals from other cells in order to survive in cult ure. In addition, we have shown that about 50 % of the oligodendrocyte s produced in the developing rat optic nerve normally die, apparently in a competition for the limiting amounts of survival factors. We have hypothesized that axons may control the levels of such oligodendrocyt e survival factors and that the competition-dependent death of oligode ndrocytes serves to match their numbers to the number of axons that th ey myelinate. Here we test one prediction of this hypothesis - that th e survival of developing oligodendrocytes depends on axons. Results: W e show that oligodendrocyte death occurs selectively in transected ner ves in which the axons degenerate. This cell death is prevented by the delivery of exogenous ciliary neurotrophic factor (CNTF) or insulin-l ike growth factor I (IGF-1), both of which have been shown to promote oligodendrocyte survival in vitro. We also show that purified neurons promote the survival of purified oligodendrocytes in vitro. Conclusion : These results strongly suggest that oligodendrocyte survival depends upon the presence of axons; they also support the hypothesis that a c ompetition for axon-dependent survival signals normally helps adjust t he number of oligodendrocytes to the number of axons that require myel ination. The identities of these signals remain to be determined.