Thus, regardless of the tissue sampled, OPC, COP, and NFOL presented as single, brain-wide common cell types. Since OPCs are the progenitors of the entire oligodendrocyte lineage, this observation demonstrates that the diversity observed among mature oligodendrocytes (Table S3) must be the result of a secondary diversification, not developmental patterning. Oligodendrocyte morphology varies according to the type of axon they myelinate, but transplantation experiments indicate that those differences are plastic (Richardson et al., 2006). This may also explain the graded, interspersed pattern of diversity among mature oligodendrocytes, in contrast to the division into cell types with clear boundaries (molecularly and anatomically) that we observed among astrocytes and neurons.
