β-Catenin-dependent transcription is central to Bmp-mediated formation of venous vessels.

β-catenin regulates the transcription of genes involved in diverse biological processes, including embryogenesis, tissue homeostasis and regeneration. Endothelial cell (EC)-specific gene-targeting analyses in mice have revealed that β-catenin is required for vascular development. However, the precise function of β-catenin-mediated gene regulation in vascular development is not well understood, since β-catenin regulates not only gene expression but also the formation of cell-cell junctions. To address this question, we have developed a novel transgenic zebrafish line that allows the visualization of β-catenin transcriptional activity specifically in ECs and discovered that β-catenin-dependent transcription is central to the bone morphogenetic protein (Bmp)-mediated formation of venous vessels. During caudal vein (CV) formation, Bmp induces the expression of aggf1, a putative causative gene for Klippel-Trenaunay syndrome, which is characterized by venous malformation and hypertrophy of bones and soft tissues. Subsequently, Aggf1 potentiates β-catenin transcriptional activity by acting as a transcriptional co-factor, suggesting that Bmp evokes β-catenin-mediated gene expression through Aggf1 expression. Bmp-mediated activation of β-catenin induces the expression of Nr2f2 (also known as Coup-TFII), a member of the nuclear receptor superfamily, to promote the differentiation of venous ECs, thereby contributing to CV formation. Furthermore, β-catenin stimulated by Bmp promotes the survival of venous ECs, but not that of arterial ECs. Collectively, these results indicate that Bmp-induced activation of β-catenin through Aggf1 regulates CV development by promoting the Nr2f2-dependent differentiation of venous ECs and their survival. This study demonstrates, for the first time, a crucial role of β-catenin-mediated gene expression in the development of venous vessels.

Kashiwada T ，Fukuhara S ，Terai K ，Tanaka T ，Wakayama Y ，Ando K ，Nakajima H ，Fukui H ，Yuge S ，Saito Y ，Gemma A ，Mochizuki N ... -  《-》

SoxF factors and Notch regulate nr2f2 gene expression during venous differentiation in zebrafish.

Initial embryonic determination of artery or vein identity is regulated by genetic factors that work in concert to specify the endothelial cell׳s (EC) fate, giving rise to two structurally unique components of the circulatory loop. The Shh/VEGF/Notch pathway is critical for arterial specification, while the orphan receptor nr2f2 (COUP-TFII) has been implicated in venous specification. Studies in mice have shown that nr2f2 is expressed in venous but not arterial ECs, and that it preferentially induces markers of venous cell fate. We have examined the role of nr2f2 during early arterial-venous development in the zebrafish trunk. We show that expression of a subset of markers of venous endothelial identity requires nr2f2, while the expression of nr2f2 itself requires sox7 and sox18 gene function. However, while sox7 and sox18 are expressed in both the cardinal vein and the dorsal aorta during early trunk development, nr2f2 is expressed only in the cardinal vein. We show that Notch signaling activity present in the dorsal aorta suppresses expression of nr2f2, restricting nr2f2-dependent promotion of venous differentiation to the cardinal vein.

Swift MR ，Pham VN ，Castranova D ，Bell K ，Poole RJ ，Weinstein BM ... -  《-》

Functional characterization of Klippel-Trenaunay syndrome gene AGGF1 identifies a novel angiogenic signaling pathway for specification of vein differentiation and angiogenesis during embryogenesis.

Chen D ，Li L ，Tu X ，Yin Z ，Wang Q ... -  《-》

Bone morphogenetic protein signaling promotes morphogenesis of blood vessels, wound epidermis, and actinotrichia during fin regeneration in zebrafish.

Zebrafish fin regeneration involves initial formation of the wound epidermis and the blastema, followed by tissue morphogenesis. The mechanisms coordinating differentiation of distinct tissues of the regenerate are poorly understood. Here, we applied pharmacologic and transgenic approaches to address the role of bone morphogenetic protein (BMP) signaling during fin restoration. To map the BMP transcriptional activity, we analyzed the expression of the evolutionarily conserved direct phospho-Smad1 target gene, id1, and its homologs id2a and id3. This analysis revealed the BMP activity in the distal blastema, wound epidermis, osteoblasts, and blood vessels of the regenerate. Blocking the BMP function with a selective chemical inhibitor of BMP type I receptors, DMH1, suppressed id1 and id3 expression and arrested regeneration after blastema formation. We identified several previously uncharacterized functions of BMP during fin regeneration. Specifically, BMP signaling is required for remodeling of plexus into structured blood vessels in the rapidly growing regenerate. It organizes the wound epithelium by triggering wnt5b expression and promoting Collagen XIV-A deposition into the basement membrane. BMP represents the first known signaling that induces actinotrichia formation in the regenerate. Our data reveal a multifaceted role of BMP for coordinated morphogenesis of distinct tissues during regeneration of a complex vertebrate appendage.

Thorimbert V ，König D ，Marro J ，Ruggiero F ，Jaźwińska A ... -  《-》

Transcription factor COUP-TFII is indispensable for venous and lymphatic development in zebrafish and Xenopus laevis.

Transcription factors play a central role in cell fate determination. Gene targeting in mice revealed that Chicken Ovalbumin Upstream Promoter-Transcription Factor II (COUP-TFII, also known as Nuclear Receptor 2F2 or NR2F2) induces a venous phenotype in endothelial cells (ECs). More recently, NR2F2 was shown to be required for initiating the expression of Prox1, responsible for lymphatic commitment of venous ECs. Small animal models like zebrafish embryos and Xenopus laevis tadpoles have been very useful to elucidate mechanisms of (lymph) vascular development. Therefore, the role of NR2F2 in (lymph) vascular development was studied by eliminating its expression in these models. Like in mice, absence of NR2F2 in zebrafish resulted in distinct vascular defects including loss of venous marker expression, major trunk vessel fusion and vascular leakage. Both in zebrafish and Xenopus the development of the main lymphatic structures was severely hampered. NR2F2 knockdown significantly decreased prox1 expression in zebrafish ECs and the same manipulation affected lymphatic (L)EC commitment, migration and function in Xenopus tadpoles. Therefore, the role of NR2F2 in EC fate determination is evolutionary conserved.

Aranguren XL ，Beerens M ，Vandevelde W ，Dewerchin M ，Carmeliet P ，Luttun A ... -  《-》