Vascularization of the mouse embryo: A study of <i>flk‐1, tek, tie</i>, and vascular endothelial growth factor expression during development

TLDR

The spongiotrophoblast compartment of the mouse placenta, situated between maternal and labyrinthine layers, expresses VEGF. This study aims to map the developmental expression patterns of endothelial receptor tyrosine kinases flk‑1, tek, tie, and the VEGF ligand, as well as the VEGF receptor flt‑1, during mouse embryogenesis and placental development. Expression was profiled by detecting transcripts of these RTKs and VEGF at half‑day intervals from embryonic day 7.0 onward, revealing sequential and spatial patterns in embryonic and extraembryonic mesoderm. The data show that flk‑1, tek, and tie transcripts appear sequentially from E7.0, are expressed in mesodermal regions that give rise to vasculature, become indistinguishable after E8.5 except in the amnion, while flt‑1 is abundant in spongiotrophoblasts, and VEGF expression overlaps with flk‑1 and extends to distant tissues, suggesting dual chemotactic and maintenance roles in vascularization. © 1995 Wiley‑Liss, Inc.

Abstract

Abstract We report the detailed developmental expression profiles of three endothelial specific receptor tyrosine kinases (RTKs) flk ‐ 1, tek, tie , as well as vascular endothelial growth factor (VEGF), the flk ‐ 1 ligand. We also examined the expression of the other VEGF receptor, flt ‐ 1 , during placental development. flk ‐ 1, tek , and tie transcripts were detected sequentially at one‐half day intervals starting at E7.0, suggesting that each of these RTKs play a unique role during vascularization of the mouse embryo. All three RTKs were expressed in the extraembryonic and embryonic mesoderm in regions that eventually give rise to the vasculature. Except for the expression of tek and flk ‐ 1 in the mesoderm of the amnion, the expression of these RTKs from E8.5 onwards was virtually indistinguishable. An abundant amount of flt ‐ 1 transcripts was found in the spongiotrophoblast cells of the developing placenta from E8.0 onwards. This cellular compartment is located between the maternal and labyrinthine layers of the placenta, which both express VEGF. VEGF transcripts were detected as early as E7.0 in the endoderm juxtaposed to the flk ‐ 1 positive mesoderm, and later in development VEGF expression displayed an expression profile both contiguous with that of flk ‐ ;1 , and also in tissues found some distance from the flk ‐ 1 ‐expressing endothelium. These results suggest a possible dual role for VEGF which includes a chemotactic and/or a cellular maintenance role for VEGF during vascularization of the mouse embryo. ©1995 Wiley‐Liss, Inc.