EXPRESSION OF PLATELET-DERIVED GROWTH-FACTOR (PDGF) AND PDGF RECEPTOR GENES IN THE DEVELOPING RAT-BRAIN

Steady-state levels of rat central nervous system (CNS) platelet-derived growth factor (PDGF) A- and B-chain mRNAs were measured by a polymerase chain reaction method employing a synthetic gene internal standard, and the rates of transcription of PDGF A- and B-chain genes in CNS were estimated by a nuclear runoff assay. The abundance of PDGF B-chain mRNA was an order of magnitude below that of PDGF A-chain mRNA, while the rate of PDGF B-chain transcription was only slightly below that for the PDGF A-chain gene, indicating that the half-life of PDGF B-chain in CNS is shorter than that of PDGF A-chain mRNA. No developmental alterations in expression of the PDGF A- and B-chain genes were detected. By contrast, Northern blots showed that steady-state levels of mRNAs encoding the two PDGF receptor proteins, alpha and beta, were markedly higher in embryonic day 15 and postnatal day 6 rat brains than in later life. These results suggest that the actions of PDGF on the brain in vivo are regulated not at the level of PDGF A and B-chain gene expression, but rather by changes in the level of expression of PDGF alpha- and beta-receptor genes.