James Darrel Kelly

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.

Relative Platelet-derived Growth Factor Receptor Subunit Expression Determines Cell Migration to Different Dimeric Forms of PDGF

Platelet-derived growth factor (PDGF) receptor transfectants of a fibroblastoid cell line (BHK) have been used to investigate the ability of the three dimeric forms of PDGF to elicit a chemotactic response. Cells transfected with the beta receptor subunit were only responsive to PDGF-BB, whereas cells expressing the alpha-receptor subunit were equally responsive to all three dimeric forms, PDGF-AA, PDGF-AB, and PDGF-BB. A positive chemotactic response correlated with rearrangement of actin organization. In a study of human arterial smooth muscle cells that express both PDGF receptor subunits endogenously, we again found that recombinant PDGF-AA could elicit a chemotactic response. However, the two smooth muscle cell isolates we examined differed in their chemotactic response to PDGF-AA. This difference correlated closely with their ability to respond mitogenically to this PDGF dimeric form, and the magnitude of both chemotactic and mitogenic responses was related to the proportion of the two receptor subunit species at the cell surface.

A scattering support for broadband sparse far field measurements

The scattering support is an estimate of the support of a source or scatterer, based on a limited set of far field measurements. In this paper, we suppose that the far field is measured at all wavenumbers, but only at a few, say N, angles ?i ?. From these measurements, we produce a ?-convex polygon (a convex polygon with normals in the ?i directions). We show that this polygon must be contained in the smallest ?-convex polygon which contains the source. We also show by explicit construction that, if (and only if) that polygon has almost 2N faces, there really is a source, supported in the ?-convex scattering support, which exactly produces these measurements.