Fig. 4. Roles of PDGF in the developing nervous and circulatory systems. (A) Oligodendrocyte precursor cell development in the mouse spinal cord. Oligodendrocyte precursor (O2A) cells, which express PDGFR, arise in the ventral periventricular zone of the mouse embryonic neural tube around E12.5. From E12.5-E15.5, O2A cells proliferate and migrate laterally and dorsally to fill the spinal cord. During this time, PDGFA is expressed by neurons and astrocytes in the spinal cord, and PDGFC is expressed by cells in the floor plate and ventral horn regions. There is evidence that PDGFA/PDGFR signaling drives O2A cell proliferation in the spinal cord (E12.5-E15.5). PDGFR signaling may also influence the migration of O2A cells. The general migration route taken by O2A progenitors is depicted by gray arrows. (B) Vascular mural cell proliferation and migration in the mouse. During angiogenesis, primitive vascular networks (or plexa) are remodeled through branching, sprouting, and pruning of the vascular endothelium. As new vessels form, they recruit and are coated by mural cells, contractile cells that support and stabilize new vessels. The two major classes of vascular mural cells are pericytes, which form single cell layers around capillaries, and vascular smooth muscle cells (VSMCs), which coat veins and arteries. During angiogenic remodeling, PDGFB is expressed in nascent vascular endothelial sprouts (a) and drives the proliferation of PDGFRß-expressing pericytes and VSMCs near arterial walls and primitive vascular plexa (b). PDGFB also directs the migration and/or survival of these mural cells along endothelial sprouts (b,c). Upon reaching their destination, VSMCs and pericytes encircle and associate tightly with the endothelium (c); survival and anti-proliferative factors produced by mural cells stabilize nascent vessels.

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