Heart field origin of great vessel precursors relies on nkx2.5-mediated vasculogenesis

The pharyngeal arch arteries (PAAs) are transient embryonic blood vessels that make indispensable contributions to the carotid arteries and great vessels of the heart, including the aorta and pulmonary artery1, 2. During embryogenesis, the PAAs appear in a craniocaudal sequence to connect pre-existing segments of the primitive circulation after de novo vasculogenic assembly from angioblast precursors3, 4. Despite the unique spatiotemporal characteristics of PAA development, the embryonic origins of PAA angioblasts and the genetic factors regulating their emergence remain unknown. Here, we identify the embryonic source of PAA endothelium as nkx2.5+ progenitors in lateral plate mesoderm long considered to adopt cell fates within the heart exclusively5, 6. Further, we report that PAA endothelial differentiation relies on Nkx2.5, a canonical cardiac transcription factor not previously implicated in blood vessel formation. Together, these studies reveal the heart field origin of PAA endothelium and attribute a novel vasculogenic function to the cardiac transcription factor nkx2.5 during great vessel precursor development

Endothelial to Mesenchymal Transition in Cardiovascular Disease: Key Mechanisms and Clinical Translation Opportunities

Endothelial to mesenchymal transition (EndMT) is a process whereby an endothelial cell undergoes a series of molecular events that lead to a change in phenotype toward a mesenchymal cell (e.g., myofibroblast, smooth muscle cell). EndMT plays a fundamental role during development, and mounting evidence indicates that EndMT is involved in adult cardiovascular diseases (CVDs), including atherosclerosis, pulmonary hypertension, valvular disease, and fibroelastosis. Therefore, the targeting of EndMT may hold therapeutic promise for treating CVD. However, the field faces a number of challenges, including the lack of a precise functional and molecular definition, a lack of understanding of the causative pathological role of EndMT in CVDs (versus being a "bystander-phenomenon"), and a lack of robust human data corroborating the extent and causality of EndMT in adult CVDs. Here, we review this emerging but exciting field, and propose a framework for its systematic advancement at the molecular and translational levels. (J Am Coll Cardiol 2019; 73: 190-209) (c) 2019 The Authors. Published by Elsevier on behalf of the American College of Cardiology Foundation

Mutant-specific gene programs in the zebrafish

Hematopoiesis involves the production of stem cells, followed by the orchestrated differentiation of the blood lineages. Genetic screens in zebrafish have identified mutants with defects that disrupt specific stages of hematopoiesis and vasculogenesis, including the cloche, spadetail (tbx16), moonshine (tif1g), bloodless, and vlad tepes (gata1) mutants. To better characterize the blood program, gene expression profiling was carried out in these mutants and in scl-morphants (scl mo). Distinct gene clusters were demarcated by stage-specific and mutant-specific gene regulation. These were found to correlate with the transcriptional program of hematopoietic progenitor cells, as well as of the erythroid, myeloid, and vascular lineages. Among these, several novel hematopoietic and vascular genes were detected, for instance, the erythroid transcription factors znfl2 and ncoa4. A specific regulation was found for myeloid genes, as they were more strongly expressed in vlt mutants compared with other erythroid mutants. A unique gene expression pattern of up-regulated isoprenoid synthesis genes was found in cloche and sclmo, possibly in migrating cells. In conjunction with the high conservation of vertebrate hematopoiesis, the comparison of transcriptional profiles in zebrafish blood mutants represents a versatile and powerful tool to elucidate the genetic regulation of blood and blood vessel development

Heart field origin of great vessel precursors relies on nkx2.5-mediated vasculogenesis

The pharyngeal arch arteries (PAAs) are transient embryonic blood vessels that make indispensable contributions to the carotid arteries and great vessels of the heart, including the aorta and pulmonary arteries. During embryogenesis, the PAAs appear in a craniocaudal sequence to connect pre-existing segments of the primitive circulation after de novo vasculogenic assembly from angioblast precursors. Despite the unique spatiotemporal characteristics of PAA development, the embryonic origins of PAA angioblasts and the genetic factors regulating their emergence remain unknown. Here, we identify the embryonic source of PAA endothelium as nkx2.5 + progenitors in lateral plate mesoderm long considered to adopt cell fates within the heart exclusively. Further, we report that PAA endothelial differentiation relies on Nkx2.5, a canonical cardiac transcription factor not previously implicated in blood vessel formation. Together, these studies reveal the heart field origin of PAA endothelium and attribute a new vasculogenic function to the cardiac transcription factor Nkx2.5 during great vessel precursor development. © 2013 Macmillan Publishers Limited

TGF-β Signaling Is Necessary and Sufficient for Pharyngeal Arch Artery Angioblast Formation

The pharyngeal arch arteries (PAAs) are transient embryonic blood vessels that mature into critical segments of the aortic arch and its branches. Although defects in PAA development cause life-threating congenital cardiovascular defects, the molecular mechanisms that orchestrate PAA morphogenesis remain unclear. Through small-molecule screening in zebrafish, we identified TGF-β signaling as indispensable for PAA development. Specifically, chemical inhibition of the TGF-β type I receptor ALK5 impairs PAA development because nkx2.5+ PAA progenitor cells fail to differentiate into tie1+ angioblasts. Consistent with this observation, we documented a burst of ALK5-mediated Smad3 phosphorylation within PAA progenitors that foreshadows angioblast emergence. Remarkably, premature induction of TGF-β receptor activity stimulates precocious angioblast differentiation, thereby demonstrating the sufficiency of this pathway for initiating the PAA progenitor to angioblast transition. More broadly, these data uncover TGF-β as a rare signaling pathway that is necessary and sufficient for angioblast lineage commitment

Fgf21 is essential for haematopoiesis in zebrafish

Fibroblast growth factors (Fgfs) function as key secreted signalling molecules in many developmental events. The zebrafish is a powerful model system for the investigation of embryonic vertebrate haematopoiesis. Although the effects of Fgf signalling on haematopoiesis in vitro have been reported, the functions of Fgf signalling in haematopoiesis in vivo remain to be explained. We identified Fgf21 in zebrafish embryos. Fgf21-knockdown zebrafish embryos lacked erythroid and myeloid cells but not blood vessels and lymphoid cells. The knockdown embryos had haemangioblasts and haematopoietic stem cells. However, the knockdown embryos had significantly fewer myeloid and erythroid progenitor cells. In contrast, Fgf21 had no significant effect on cell proliferation and apoptosis in the intermediate cell mass. These results indicate that Fgf21 is a newly identified factor essential for the determination of myelo-erythroid progenitor cell fate in vivo