Distinct effects of bFGF and PDGF on oligodendrocyte progenitor cells

We have compared the effects of platelet‐derived (PDGF) and basic fibroblast (bFGF) growth factors on the shape, migration, and differentiation of oligodendrocyte progenitor cells, the precursors of myelin‐forming cells in the CNS. In the presence of bFGF, oligodendrocyte progenitors purified from rat neonatal brain cultures were stellate, non‐motile, and had a morphological complexity of 1.26 ± 0.03 as measured by fractal dimension (D). These cells expressed transcripts encoding the POU‐homeodomain transcription factor Oct‐6, but not myelin genes. Upon addition of PDGF, bFGF‐treated cells became motile and twofold less complex in shape (D = 1.19 ± 0.03). These changes occurred within 6 ± 4 h and were dependent on de novo transcription and translation, but not DNA synthesis. Upon removal of PDGF the cells reverted to their stellate shape (D = 1.26). Removal of both bFGF and PDGF resulted in oligodendrocyte differentiation after 3 days, with a fourfold increase in complexity of shape (D = 1.55 ± 0.08), loss of Oct‐6 transcripts, and gain of myelin transcripts. Thus PDGF is both necessary and sufficient to induce a motile state in progenitor cells growing in the presence of bFGF. Together with our previous data (McKinnon et al.: Neuron 5:603, 1990), our results suggest that bFGF and PDGF may control distinct phases of proliferation and migration of oligodendrocyte progenitor cells in vivo.