FIGURE 4.

OPC differentiation and apoptosis are highly regulated by external signals. Nestin positive polypotent NSC differentiate into lineage specific OPC that give rise to pre-myelinating (P-OL) or undergo apoptosis. P-OL then differentiate into mature OL. These processes are tightly controlled by diffusible and non-diffusible molecules expressed by active or non-active axons. These instructive molecules can promote (black ↑) or inhibit (red ⊥) these processes by altering gene expression in these cells (shown as a box with matching color). Genes and proteins shown represent only a partial list of key molecules discussed in the text. For more comprehensive reviews see Mitew et al. (2014), Foster et al. (2019). NSC, polypotent neural stem cell; OPC, oligodendrocyte progenitor cells; P-OL, pre-myelinating oligodendrocytes; OL, mature oligodendrocytes.