Alternatively Spliced Tissue Factor Is Not Sufficient for Embryonic Development

Abstract

Tissue factor (TF) triggers blood coagulation and is translated from two mRNA splice isoforms, encoding membrane-anchored full-length TF (flTF) and soluble alternatively-spliced TF (asTF). The complete knockout of TF in mice causes embryonic lethality associated with failure of the yolk sac vasculature. Although asTF plays roles in postnatal angiogenesis, it is unknown whether it activates coagulation sufficiently or makes previously unrecognized contributions to sustaining integrity of embryonic yolk sac vessels. Using gene knock-in into the mouse TF locus, homozygous asTF knock-in (asTFKI) mice, which express murine asTF in the absence of flTF, exhibited embryonic lethality between day 9.5 and 10.5. Day 9.5 homozygous asTFKI embryos expressed asTF protein, but no procoagulant activity was detectable in a plasma clotting assay. Although the α-smooth-muscle-actin positive mesodermal layer as well as blood islands developed similarly in day 8.5 wild-type or homozygous asTFKI embryos, erythrocytes were progressively lost from disintegrating yolk sac vessels of asTFKI embryos by day 10.5. These data show that in the absence of flTF, asTF expressed during embryonic development has no measurable procoagulant activity, does not support embryonic vessel stability by non-coagulant mechanisms, and fails to maintain a functional vasculature and embryonic survival.

Tissue factor at the crossroad of coagulation and cell signaling

“…Although alternatively spliced TF (asTF) does not support physiological roles of TF (e.g. in embryonic development ), it retains the ability to ligate integrins αvβ3 and α6β1 , which also interact with full‐length TF . Signaling of asTF is independent of FVIIa‐PAR2 and promotes, through direct integrin ligation of endothelial cells, angiogenesis and inflammation , or cancer cell survival .…”

Targeting clotting proteins in cancer therapy – progress and challenges

“…The alternative splicing of TF preserves binding with αvβ3 and α6β1 and soluble asTF can enhance tumorigenicity of luminal breast cancer cells through autocrine integrin β1 signaling as well as through endothelial cell αvβ3 ligation promoting sprouting angiogenesis and upregulation of myeloid cell adhesion molecules (68-70). While integrin ligation pathways of asTF and transmembrane TF are overlapping, asTF, unlike full-length TF, cannot rescue early embryonic failure of the yolk sac vasculature caused by TF-deficiency in mice (71). …”

Hemostasis and endothelial functionality: the double face of coagulation factors

“…34 Congruently, as-TF promotes cancer proliferation through integrin β1 signaling, further highlighting the pivotal interconnection of CFs with integrins. 35 However, as-TF alone is not enough to promote the correct formation of the vasculature during embryogenesis, 36 suggesting that both isoforms are necessary to regulate blood vessel formation and maintenance. Indeed, already in 1996 it was demonstrated that fl-TF −/− mice dye during embryonic development due to vascular failure.…”

“…However, as-TF alone is not enough to promote the correct formation of the vasculature during embryogenesis, 36 suggesting that both isoforms are necessary to regulate blood vessel formation and maintenance. Indeed, already in 1996, it was demonstrated that fl-TF -/ - mice die during embryonic development due to vascular failure.…”