Dominant-negative and targeted null mutations in the endothelial receptor tyrosine kinase, tek, reveal a critical role in vasculogenesis of the embryo.

Abstract

The receptor tyrosine kinases (RTKs) expressed on the surface of endothelial cells are likely to play key roles in initiating the program of endothelial cell growth during development and subsequent vascularization during wound healing and tumorigenesis. Expression of the Tek RTK during mouse development is restricted primarily to endothelial cells and their progenitors, the angioblasts, suggesting that Tek is a key participant in vasculogenesis. To investigate the role that Tek plays within the endothelial cell lineage, we have disrupted the Tek signaling pathway using two different genetic approaches. First, we constructed transgenic mice expressing a dominant-negative form of the Tek receptor. Second, we created a null allele of the tek gene by homologous recombination in embryonic stem (ES) cells. Transgenic mice expressing dominant-negative alleles of Tek or homozygous for a null allele of the tek locus both died in utero with similar defects in the integrity of their endothelium. By crossing transgenic mice that express the lacZ reporter gene under the transcriptional control of the endothelial cell-specific tek promoter, we found that the extraembryonic and embryonic vasculature was patterned correctly. However, homozygous tek embryos had -30% and 75% fewer endothelial cells at day 8.5 and 9.0, respectively. Homozygous null embryos also displayed abnormalities in heart development, consistent with the conclusion that Tek is necessary for endocardial/myocardial interactions during development. On the basis of the analysis of mice carrying either dominant-negative or null mutations of the tek gene, these observations demonstrate that the Tek signaling pathway plays a critical role in the differentiation, proliferation, and survival of endothelial cells in the mouse embryo.

MAP3Ks as central regulators of cell fate during development

“…Mutant embryos show excessive apoptosis of endothelial cells resulting in irregularly shaped blood vessels which leads to reduced blood circulation and hemorrhage into major body cavities (Wojnowski et al, 1997). The B-Raf-deficient phenotype is similar to that observed in mice lacking Tie2, a receptor tyrosine kinase involved in vasculogenesis (Dumont et al, 1994). This suggests that B-Raf may be activated by Tie2 signaling.…”

Cotargeting of VEGFR-1 and -3 and angiopoietin receptor Tie2 reduces the growth of solid human ovarian cancer in mice

“…Previous studies have shown that Tie1-deficient mice die because of edema and hemorrages resulting from poor structural integrity of endothelial cells. 44 Tie2-deficient mice have immature vessels that lack branching networks and periendothelial support cells. 44,45 In our earlier study with sVEGFR-1, -2 and -3, 25 we did not notice such liver toxicity.…”

“…44 Tie2-deficient mice have immature vessels that lack branching networks and periendothelial support cells. 44,45 In our earlier study with sVEGFR-1, -2 and -3, 25 we did not notice such liver toxicity. In the combination group V (sVEGFR-1, -3 and sTie2), a tendency towards a greater amount of ascites was found and 63% of the mice presented edema under the skin.…”

The Tek/Tie2 receptor signals through a novel Dok-related docking protein, Dok-R

“…These RTKs are expressed in di erent spatial and temporal patterns during development (Dumont et al, 1995), suggesting that they play distinct roles within the endothelial cell lineage. This subgroup of RTKs has been placed into two subfamilies according to similarities in their primary amino acid sequences (Dumont et al, 1993;Mustonen and Alitalo, 1995). The ®rst subfamily contains the high a nity vascular endothelial growth factor receptors (VEGFRs), known as Flk-1/KDR/VEGFR2, Flt-1/VEGFR1, and Flt-4/ VEGFR3, and the second subfamily consists of the TIE receptors, known as Tie/Tie1 and Tek/Tie2.…”