XB-ART-37831Dev Biol. June 15, 2006; 294 (2): 458-70.
The forkhead transcription factors, Foxc1 and Foxc2, are required for arterial specification and lymphatic sprouting during vascular development.
Accumulating evidence suggests that in the vertebrate embryo, acquisition of arterial and venous identity is established early by genetic mechanisms, including those regulated by vascular endothelial growth factor (VEGF) and Notch signaling. However, although the COUP-TFII nuclear receptor has recently been shown to regulate vein identity, very little is known about the molecular mechanisms of transcriptional regulation in arterial specification. Here, we show that mouse embryos compound mutant for Foxc1 and Foxc2, two closely related Fox transcription factors, exhibit arteriovenous malformations and lack of induction of arterial markers whereas venous markers such as COUP-TFII are normally expressed, suggesting that mutant endothelial cells fail to acquire an arterial fate. Notably, consistent with this observation, overexpression of Foxc genes in vitro induces expression of arterial markers such as Notch1 and its ligand Delta-like 4 (Dll4), and Foxc1 and Foxc2 directly activate the Dll4 promoter via a Foxc-binding site. Moreover, compound Foxc mutants show a defect in sprouting of lymphatic endothelial cells from veins in early lymphatic development, due to reduced expression of VEGF-C. Taken together, our results demonstrate that Foxc transcription factors are novel regulators of arterial cell specification upstream of Notch signaling and lymphatic sprouting during embryonic development.
PubMed ID: 16678147
Article link: Dev Biol.
Genes referenced: dll4 flt4 foxc1 foxc2 notch1 nr2f5 prox1 sacs vegfa vegfc
Article Images: [+] show captions
|Fig. 3. Defective lymphatic vessel development in compound Foxc1+/−; Foxc2−/− mutants. (A–D) Immunohistochemical analysis to detect a lymphatic endothelial cell marker, Prox1, using transverse sections at the level of the heart at E10.5 (A, B) and E11.5 (C, D). (A, B) Although compound Foxc1+/−; Foxc2−/− mutant embryos (B) show the budding of lymphatic endothelial cells (arrows) from the cardinal vein, the number of Prox1-positive cells appears to be reduced compared to the wild type (A). (C, D) At E11.5, wild-type embryos (C) have well-formed lymph sacs (asterisks) and the sprouting of lymphatic endothelial cells (arrows). By contrast, abnormal formation of the lymph sacs and the reduced sprouting of lymphatic endothelial cells are observed in compound Foxc1+/−; Foxc2−/− mutants (D). (E) Quantitative analysis of Prox1-positive cells in wild-type and compound Foxc1+/−; Foxc2−/− mutant embryos at E10.5 and E11.5. The number of Prox1-positive cells is significantly reduced in compound Foxc1+/−; Foxc2−/− mutants at both E10.5 (P < 0.01) and E11.5 (P < 0.01). Data are collected from three embryos per genotype. (F–M) Section in situ hybridization at E10.5 (F–I) and E11.5 (J–M) at the level of the heart. In adjacent sections of wild-type embryo at E10.5 (F–H), expression domains of Foxc1 (F) and Foxc2 (G) in the developing lymphatic region are partially overlapped with those of VEGF-C (H) as indicated by arrows. VEGF-C expression is significantly reduced in compound Foxc1+/−; Foxc2−/− mutant embryos at E10.5 (I) and E11.5 (K), compared to wild-type embryos (H, J). By contrast, expression levels of VEGFR-3 in lymphatic endothelial cells (arrowheads) are normal in compound Foxc1+/−; Foxc2−/− mutant (M), compared to wild-type embryo (L). cv, cardinal vein; da, dorsal aorta. Scale bars, 50 μm (A–D) and 100 μm (I and M).|