Molecular identification of venous progenitors in the dorsal aorta reveals an aortic origin for the cardinal vein in mammals

Abstract

Coordinated arterial-venous differentiation is crucial for vascular development and function. The origin of the cardinal vein (CV) in mammals is unknown, while conflicting theories have been reported in chick and zebrafish. Here, we provide the first molecular characterization of endothelial cells (ECs) expressing venous molecular markers, or venous-fated ECs, within the emergent dorsal aorta (DA). These ECs, expressing the venous molecular markers Coup-TFII and EphB4, cohabited the early DA with ECs expressing the arterial molecular markers ephrin B2, Notch and connexin 40. These mixed ECs in the early DA expressed either the arterial or venous molecular marker, but rarely both. Subsequently, the DA exhibited uniform arterial markers. Real-time imaging of mouse embryos revealed EC movement from the DA to the CV during the stage when venous-fated ECs occupied the DA. We analyzed mutants for EphB4, which encodes a receptor tyrosine kinase for the ephrin B2 ligand, as we hypothesized that ephrin B2/EphB4 signaling may mediate the repulsion of venous-fated ECs from the DA to the CV. Using an EC quantification approach, we discovered that venousfated ECs increased in the DA and decreased in the CV in the mutants, whereas the rest of the ECs in each vessel were unaffected. This result suggests that the venous-fated ECs were retained in the DA and missing in the CV in the EphB4 mutant, and thus that ephrin B2/EphB4 signaling normally functions to clear venous-fated ECs from the DA to the CV by cell repulsion. Therefore, our cellular and molecular evidence suggests that the DA harbors venous progenitors that move to participate in CV formation, and that ephrin B2/EphB4 signaling regulates this aortic contribution to the mammalian CV.

Development of the lymphatic system: new questions and paradigms

“…Later on, a subpopulation of venous-fated angioblasts in the DA sprouts ventrally to give rise to the PCV (Herbert et al, 2009;Jin et al, 2005). Most recently, a study conducted in mice demonstrated that at least ∼15% of the CV cells originate in the DA (Lindskog et al, 2014; reviewed by Potente et al, 2011). In line with the findings of Herbert et al (2009), this work demonstrated that the DA harbors a heterogeneous population of venous and arterial ECs early during vasculogenesis, with the venous ECs being those that generate the CV (Lindskog et al, 2014).…”

Constitutively active Notch4 receptor elicits brain arteriovenous malformations through enlargement of capillary-like vessels

“…The Notch receptors are transmembrane proteins that promote arterial endothelial cell (EC) specification by enhancing expression of arterial molecular markers and suppressing the expression of venous markers (12)(13)(14)(15)(16)(17)(18)(19). Abnormal signaling induces enlarged AV connections and shunting in mouse and zebrafish embryos (12)(13)(14).…”

“…Abnormal signaling induces enlarged AV connections and shunting in mouse and zebrafish embryos (12)(13)(14). Notch activity is aberrantly increased in the endothelium of human brain AVMs (18,20), suggesting that it may participate in the growth or maintenance of human AVMs.…”

The Role of EphB4 and Ephrin-B2 Interactions in Prostate Cancer Models of Intravasation and Extravasation

“…The modelling of two major vessels, the dorsal aorta and the cardinal vein, during embryonic development requires repulsive signalling between ephrin-B2 and EphB4 in endothelial cells (ECs) [101,102]. Initially shown in zebrafish [103], and then in mouse [104], the dorsal aorta forms first and harbours a mixed population of venous (EphB4+) and arterial progenitors (ephrin-B2+). Both studies have shown that the formation of the cardinal vein is regulated by repulsive signalling between EphB4 and ephrin-B2.…”

“…Signalling between both EphB4 and ephrin-B2 repels venous ECs from arterial ECs generating an EphB4+ cardinal vein [103,104]. During the early stages of embryo development lymphatic ECs differentiate from the cardinal vein and other venous derivatives [105].…”