Origin, Specification, and Plasticity of the Great Vessels of the Heart

Abstract

SUMMARY The pharyngeal arch arteries (PAAs) are a series of paired embryonic blood vessels that give rise to several major arteries that connect directly to the heart. During development, the PAAs emerge from nkx2.5-expressing mesodermal cells and connect the dorsal head vasculature to the outflow tract of the heart. Despite their central role in establishing the circulatory system, the embryonic origins of the PAA progenitors are only coarsely defined, and the factors that specify them and their regenerative potential are unclear. Using fate mapping and mutant analysis, we find that PAA progenitors are derived from the tcf21 and nkx2.5 double-positive head mesoderm and require these two transcription factors for their specification and survival. Unexpectedly, cell ablation shows that the tcf21+; nkx2.5+ PAA progenitors are not required for PAA formation. We find that this compensation is due to the replacement of ablated tcf21+; nkx2.5+ PAA cells by endothelial cells from the dorsal head vasculature. Together, these studies assign the embryonic origin of the great vessel progenitors to the interface between the pharyngeal and cardiac mesoderm, identify the transcription factor code required for their specification, and reveal an unexpected plasticity in the formation of the great vessels.

Internal epitope tagging informed by relative lack of sequence conservation

“…We therefore performed whole mount immunohistochemistry using V5 tag-specific antibodies. Internally epitope tagged Tcf21 was readily detectable in an expression pattern consistent with the previously published mRNA expression pattern151718 (Fig. 4e,f).…”

“…Second, at least five of the F1s positive for tag integration harbored frameshift mutations in the second copy of the gene. We proceeded to cross F1s heterozygous for tag integrations to each other as well as other F1 fish, and observed that in each of the crosses where both parents were heterozygous for a frameshift mutation, approximately 25% of the embryos displayed a branchial arch malformation phenotype consistent with the recently published tcf21 mutant18 and morphant17 phenotypes (Fig. 4b,d).…”

“…Interestingly, overexpression of tcf21 results in increased tbx18 expression, though it is not clear if this is a direct effect14. In addition to the proepicardial organ, tcf21 is expressed in myoblast precursors in the branchial arches15161718, while expression of tbx18 is most pronounced in the developing pectoral fin bud19. In adult zebrafish, tcf21 is constitutively expressed in the epicardium, and ablation of tcf21 -expressing epicardial cells leads to loss of the regenerative capacity of the zebrafish heart20.…”

The pro-inflammatory signalling regulator Stat4 promotes vasculogenesis of great vessels derived from endothelial precursors

“…However, lack of stat4 prevents proliferation of nkx2.5 + cells and eventually results in stenosis of the primitive GVs. A previous study showed that tcf21 , together with nkx2.5 , marked a group of PAA progenitor cells, but the tcf21 + nkx2.5 + progenitors were not required for PAA formation10. In this study, we found that genetic ablation of stat4 did not affect the tcf21 -expressing PAA cells.…”

Molecular Basis for Dysregulated Activation of NKX2‐5 in the Vascular Remodeling of Systemic Sclerosis

“…Chromatin was immunoprecipitated using specific antibodies. Five primer pairs 1, 2, 3, 4, 5 were designed to cover the 1.6‐kb genomic region of the downstream enhancer. Results are shown as the fold enrichment of each protein in every genomic segment.…”