PDGF AND ITS RECEPTORS IN THE DEVELOPING RODENT RETINA AND OPTIC-NERVE

We have used in situ hybridization to visualize cells in the developin g rat retina and optic nerve that express mRNAs encoding the A and B c hains of platelet-derived growth factor (PDGF-A and PDGF-B), and the a lpha and beta subunits of the PDGF receptor (PDGF-alphaR and PDGF-beta R). We have also visualized PDGF-A protein in these tissues by immunoh istochemistry. In the retina, PDGF-A mRNA is present in pigment epithe lial cells, ganglion neurons and a subset of amacrine neurons. PDGF-A transcripts accumulate in ganglion neurons during target innervation a nd in amacrine neurons around the time of eye opening, suggesting that PDGF-A expression in these cells may be regulated by target-derived s ignals or by electrical activity. In the mouse retina, PDGF-A immunore activity is present in the cell bodies, dendrites and proximal axons o f ganglion neurons, and throughout the inner nuclear layer. PDGF-alpha R mRNA is expressed in the retina by astrocytes in the optic fibre lay er and by a subset of cells in the inner nuclear layer that might be M uller glia or bipolar neurons. Taken together, our data suggest short- range paracrine interactions between PDGF-A and PDGF-alphaR, the ligan d 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 -alphaR+ cells in the optic nerve first appear near the optic chiasm a nd subsequently spread to the retinal end of the nerve; these PDGF-alp haR+ cells are probably oligodendrocyte precursors (Pringle et al., 19 92). RNA transcripts encoding PDGF-B and PDGF-betaR are expressed by c ells of the hyaloid and mature vascular systems in the eye and optic n erve.