Selective expression of PDGF A and its receptor during early mouse embryogenesis.

Murine homologs of the PDGF A, PDGF B, and PDGF receptor alpha subunit genes were cloned. These were used, together with a mouse PDGF receptor beta subunit cDNA clone, to monitor gene expression in early postimplantation mouse embryos and in F9 embryonal carcinoma cells. RNAse protection analysis shows that PDGF A chain, but not B chain, mRNA is expressed in 6.5- to 8.5-day embryonic and extraembryonic tissues. Both alpha and beta receptor subunit mRNAs are expressed in early embryos, however, alpha subunit mRNA appears earlier and is more abundant than beta subunit mRNA. Undifferentiated F9 embryonal carcinoma stem cells express abundant levels of A chain, but not B chain, mRNA. Neither of the PDGF receptor genes is expressed in stem cells. Treatment with retinoic acid stimulates expression of both PDGF receptor genes. As in postimplantation mouse embryos, alpha receptor subunit mRNA appears earlier and is substantially more abundant than beta subunit mRNA. Collectively, these data demonstrate that the genes encoding the two chains of PDGF and their receptors are regulated independently during development and suggest that the two systems have some nonoverlapping functions in vivo. PDGF A, but not PDGF B, may be particularly important in modulating early events in mouse embryonic development.