Coordinate expression of vascular endothelial growth factor receptor‐1 (fit‐1) and its ligand suggests a paracrine regulation of murine vascular development

Abstract

Vascular endothelial growth factor (VEGF) is a candidate regulator of blood vessel growth during embryonic development and in tumors. To evaluate the role of VEGF receptor-l/ flt-1 (VEGFRl/flt-1) in the development of the vascular system, we have characterized the murine homolog of the human flt-1 gene and have analyzed its expression pattern during mouse embryogenesis. Receptor binding studies using transfected COS cells revealed that the murine flt-1 gene encodes a high affinity receptor for VEGF. The apparent K, for VEGF binding, as determined by Scatchard analysis, was 114 pM, demonstrating that VEGFRl/flt-1 has a higher affinity to VEGF than VEGF receptor-2/flk-l (VEGFR2/flk-l). By in situ hybridization, VEGFRl/flt-1 was detected in the yolk sac mesoderm already at the early stages of vascular development, while the receptor ligand was expressed in the entire endoderm of 7.5-day mouse embryos. A comparison with VEGFR2/flk-1 showed that the two receptors shared a common expression domain in the yolk sac mesoderm, but were expressed at different sites in the ectoplacental cone. The differential expression of the two VEGF receptors persisted in the developing placenta, where VEGFRl/flt-1 mRNA was detected in the spongiotrophoblast layer, whereas VEGFR2/ flk-1 transcripts were present in the labyrinthine layer which is the site of VEGF expression. In the embryo proper, VEGFRlIflt-1 mRNA was specifically localized in blood vessels and capillaries of the developing organs, closely resembling the pattern of VEGFR2/flk-1 transcript distribution. In the developing brain, the expression of VEGF receptors in the perineural capillary plexus and in capillary sprouts which have invaded the neuroectoderm correlated with endothelial cell proliferation and brain angiogenesis. The data are consistent with the hypothesis that VEGF and its receptors have an important function both in the differentiation of the endothelial lineage and in the neovascularization of developing organs, and act in a paracrine fashion. o 1995 Wiley-Liss, Inc.

Development and malignant progression of astrocytomas in GFAP-v-src transgenic mice

“…Sense and antisense RNA probes were transcribed in vitro with T3 and T7 RNA polymerase from linearized pBlusescript vectors carrying cDNAs for v-src, GFAP (Lewis et al, 1984), synaptophysin (Leube et al, 1989), proteolipid protein (Milner et al, 1985), VEGF (Breier et al, 1992),¯k-1 and¯t-1 (Breier et al, 1995) in the presence of digoxigenin-11-dUTP (Boehringer Mannheim). 50 ± 200 ng of labeled transcripts (0.7 ± 1.2 kb) were hybridized to tissue sections at 658C as described (Marino et al, 1995).…”

Early Induction of Angiogenetic Signals in Gliomas of GFAP-v-src Transgenic Mice

“…Sense and antisense RNA probes were transcribed in vitro with T3 and T7 RNA polymerase from linearized pBluescript vectors carrying cDNAs for v-src (700 bp), GFAP 24 (1200 bp), VEGF 25 (600 bp), flk-1 26 (2600 bp), flt-1 27 (2000 bp), tie-1 (600 bp), and tie-2 (1200 bp) 28 in the presence of digoxigenin-11-dUTP (Boehringer Mannheim). As described, 400 to 800 ng of labeled transcripts (0.6 to 2.6 kb) were hybridized to tissue sections at 65°C.…”

Homologous Up-regulation of KDR/Flk-1 Receptor Expression by Vascular Endothelial Growth Factor in Vitro

“…1). Although VEGF is expressed in various cell types, KDR/Flk-1 and Flt-1 expression is primarily restricted to vascular endothelial cells (1)(2)(3)(4)(5)(6)(7)(8). Up-regulation of VEGF and its receptors has been observed in tumors and in various conditions such as hypoxia and wound healing (1, 9 -16), whereas relatively low levels are expressed in the blood vessels of normal adult tissues (17).…”