OPCs are derived from neural tube precursors that are patterned along the anteroposterior axis. This has been demonstrated clearly, e.g., by genetic lineage tracing of Emx1-positive neural progenitors, which selectively labels forebrain oligodendrocytes (Kessaris et al., 2006). Thus, at some point, cells that later become OPCs must have been molecularly distinct along the anteroposterior axis, for example, expressing Emx1 in the forebrain, En1 in the midbrain, and Hox genes in the hindbrain and spinal cord. Yet this did not translate into distinct OPC types along the same axis. Clearly, at some point, anteroposterior patterning must be lost in the oligodendrocyte lineage. We therefore asked if, despite the lack of clearly distinct subtypes, OPCs, COPs, or NFOLs sampled from different tissues retained any traces of patterning gene expression (Figure 4D). We confirmed induction of the key transcription factor Sox10 in OPCs and of the myelin oligodendrocyte glycoprotein Mog in COPs. In the spinal cord, we detected a clear expression of Hox genes 6–10 (that is, Hoxa6, Hoxb6, …, Hoxd10), which are responsible for patterning the thoracic spinal cord. These genes were
