Summary
We have used in situ hybridization to visualize cells in the developing rat retina and optic nerve that express mRNAs encoding the A and B chains of platelet-derived growth factor (PDGF-A and PDGF-B), and the alpha and beta subunits of the PDGF receptor (PDGF-alpha R and PDGF-beta R). We have also visualized PDGF-A protein in these tissues by immunohistochemistry. In the retina, PDGF-A mRNA is present in pigment epithelial cells, ganglion neurons and a subset of amacrine neurons. PDGF-A transcripts accumulate in ganglion neurons during target innervation and in amacrine neurons around the time of eye opening, suggesting that PDGF-A expression in these cells may be regulated by target-derived signals or by electrical activity. In the mouse retina, PDGF-A immunoreactivity is present in the cell bodies, dendrites and proximal axons of ganglion neurons, and throughout the inner nuclear layer. PDGF-alpha R mRNA is expressed in the retina by astrocytes in the optic fibre layer and by a subset of cells in the inner nuclear layer that might be Muller glia or bipolar neurons. Taken together, our data suggest short-range paracrine interactions between PDGF-A and PDGF-alpha R, the ligand and its receptor being expressed in neighbouring layers of cells in the retina. In the optic nerve, PDGF-A immunoreactivity is present in astrocytes but apparently not in the retinal ganglion cell axons. PDGF-alpha R+ cells in the optic nerve first appear near the optic chiasm and subsequently spread to the retinal end of the nerve; these PDGF-alpha R+ cells are probably oligodendrocyte precursors (Pringle et al., 1992). RNA transcripts encoding PDGF-B and PDGF-beta R are expressed by cells of the hyaloid and mature vascular systems in the eye and optic nerve.