[Show abstract][Hide abstract] ABSTRACT: Septal defects and coronary vessel anomalies are common congenital heart defects, yet their ontogeny and the underlying genetic mechanisms are not well understood. Here, we investigated the role of chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII, NR2F2) in cardiac organogenesis.
We analyzed embryos deficient in COUP-TFII and observed a spectrum of cardiac defects, including atrioventricular septal defect, thin-walled myocardium, and abnormal coronary morphogenesis. We show by expression analysis that COUP-TFII is expressed in the endocardium and the epicardium but not in the myocardium of the ventricle. Using endothelial-specific COUP-TFII mutants and molecular approaches, we show that COUP-TFII deficiency resulted in endocardial cushion hypoplasia. This was attributed to the reduced growth and survival of atrioventricular cushion mesenchymal cells and defective epithelial-mesenchymal transformation (EMT) in the underlying endocardium. In addition, the endocardial EMT defect was accompanied by downregulation of Snai1, one of the master regulators of EMT, and upregulation of vascular endothelial-cadherin. Furthermore, we show that although COUP-TFII does not play a major role in the formation of epicardial cell cysts, it is critically important for the formation of epicardium. Ablation of COUP-TFII impairs epicardial EMT and coronary plexus formation.
Our results reveal that COUP-TFII plays cell-autonomous roles in the endocardium and the epicardium for endocardial and epicardial EMT, which are required for proper valve and coronary vessel formation during heart development.
[Show abstract][Hide abstract] ABSTRACT: Chicken ovalbumin upstream promoter transcription factors (COUP-TFs) belong to the steroid/thyroid hormone receptor superfamily. Cloning of their cDNAs demonstrated the existence of two distinct but related genes: COUP-TFI (EAR-3, NR2F1) and COUP-TFII (ARP-1, NR2F2). They are referred to as orphan receptors because ligands for COUP-TFs have yet to be identified. Since 1998, extensive studies have demonstrated their physiological importance in cell-fate specification, organogenesis, angiogenesis, and metabolism, as well as a variety of diseases. In this article, we will comprehensively review the biological functions of COUP-TFII and its underlying mechanism in various developmental processes and diseases. In addition, we will briefly summarize some of the current findings of COUP-TFI.
No preview · Article · Jun 2011 · Endocrine reviews
[Show abstract][Hide abstract] ABSTRACT: The lymphatic system plays a key role in tissue fluid homeostasis. Lymphatic dysfunction contributes to the pathogenesis of many human diseases, including lymphedema and tumor metastasis. However, the mechanisms regulating lymphangiogenesis remain largely unknown. Here, we show that COUP-TFII (also known as Nr2f2), an orphan member of the nuclear receptor superfamily, mediates both developmental and pathological lymphangiogenesis in mice. Conditional ablation of COUP-TFII at an early embryonic stage resulted in failed formation of pre-lymphatic ECs (pre-LECs) and lymphatic vessels. COUP-TFII deficiency at a late developmental stage resulted in loss of LEC identity, gain of blood EC fate, and impaired lymphatic vessel sprouting. siRNA-mediated downregulation of COUP-TFII in cultured primary human LECs demonstrated that the maintenance of lymphatic identity and VEGF-C-induced lymphangiogenic activity, including cell proliferation and migration, are COUP-TFII-dependent and cell-autonomous processes. COUP-TFII enhanced the pro-lymphangiogenic actions of VEGF-C, at least in part by directly stimulating expression of neuropilin-2, a coreceptor for VEGF-C. In addition, COUP-TFII inactivation in a mammary gland mouse tumor model resulted in inhibition of tumor lymphangiogenesis, suggesting that COUP-TFII also regulates neo-lymphangiogenesis in the adult. Thus, COUP-TFII is a critical factor that controls lymphangiogenesis in embryonic development and tumorigenesis in adults.
Full-text · Article · Apr 2010 · The Journal of clinical investigation
[Show abstract][Hide abstract] ABSTRACT: How arterial and venous fates are established is largely unknown. In the past, circulatory dynamics were thought to be the exclusive cause of arteries and veins being structurally and functionally distinct; however, growing evidence indicates that an orderly progression of molecular signals controls arterial-venous specification in the developing vertebrate vascular system.
[Show abstract][Hide abstract] ABSTRACT: The origin of the mammalian lymphatic vasculature has been debated for more than 100 years. Whether lymphatic endothelial cells have a single or dual, venous or mesenchymal origin remains controversial. To resolve this debate, we performed Cre/loxP-based lineage-tracing studies using mouse strains expressing Cre recombinase under the control of the Tie2, Runx1, or Prox1 promoter elements. These studies, together with the analysis of Runx1-mutant embryos lacking definitive hematopoiesis, conclusively determined that from venous-derived lymph sacs, lymphatic endothelial cells sprouted, proliferated, and migrated to give rise to the entire lymphatic vasculature, and that hematopoietic cells did not contribute to the developing lymph sacs. We conclude that the mammalian lymphatic system has a solely venous origin.
Full-text · Article · Nov 2007 · Genes & Development
[Show abstract][Hide abstract] ABSTRACT: Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) is a member of the orphan nuclear receptor superfamily. The spatiotemporal expression pattern of COUP-TFII suggests that it participates in mesenchymal-epithelial interactions required for organogenesis. The null mutants of COUP-TFII die around embryonic (E) day E10 due to defects in angiogenesis and heart formation. To further understand the biologic functions of COUP-TFII during development, LacZ knockin mice and floxed COUP-TFII mice were generated. 5-bomo-4-chloro-3-indolyl--D-galactopyranoside (X-gal) staining of COUP-TFII–LacZ knockin mice shows high COUP-TFII expression in the endothelium of the vein but not in the artery. In contrast, COUP-TFII is highly expressed in the smooth muscle layer surrounding the artery. This differential expression pattern suggests that COUP-TFII may play a role in establishing arterial-venous identity. To further elucidate the functional role of COUP-TFII in the formation of endothelium of the vein, COUP-TFII was specifically knocked out in the endothelium using Tie-2 Cre mice. In mutant mice lacking COUP-TFII in the endothelium, the vein acquires arterial characteristics and ectopic expression of Notch signal pathway. In addition, NP-1, an upstream regulator of Notch signaling, is also up-regulated. Finally, ectopic formation of hematopieitic cell clusters (HCC) is observed in the mutant veins. Our results are consistent with the notion that cell fate determination of the vein is under genetic control rather than deriving from a default pathway as proposed previously. In addition, COUP-TFII is the first transcription factor identified that specifically marks the endothelium of the vein. Understanding the role of COUP-TFII during the vasculature development will provide insights into the molecular mechanism for the establishment of arterial-venous identity.
Preview · Article · Oct 2005 · Kidney International
[Show abstract][Hide abstract] ABSTRACT: Arteries and veins are anatomically, functionally and molecularly distinct. The current model of arterial-venous identity proposes that binding of vascular endothelial growth factor to its heterodimeric receptor--Flk1 and neuropilin 1 (NP-1; also called Nrp1)--activates the Notch signalling pathway in the endothelium, causing induction of ephrin B2 expression and suppression of ephrin receptor B4 expression to establish arterial identity. Little is known about vein identity except that it involves ephrin receptor B4 expression, because Notch signalling is not activated in veins; an unresolved question is how vein identity is regulated. Here, we show that COUP-TFII (also known as Nr2f2), a member of the orphan nuclear receptor superfamily, is specifically expressed in venous but not arterial endothelium. Ablation of COUP-TFII in endothelial cells enables veins to acquire arterial characteristics, including the expression of arterial markers NP-1 and Notch signalling molecules, and the generation of haematopoietic cell clusters. Furthermore, ectopic expression of COUP-TFII in endothelial cells results in the fusion of veins and arteries in transgenic mouse embryos. Thus, COUP-TFII has a critical role in repressing Notch signalling to maintain vein identity, which suggests that vein identity is under genetic control and is not derived by a default pathway.