Endothelin receptor type A expression defines a distinct cardiac subdomain within the heart field and is later implicated in chamber myocardium formation

Endothelin signaling in development

Since the discovery of endothelin 1 (EDN1) in 1988, the role of endothelin ligands and their receptors in the regulation of blood pressure in normal and disease states has been extensively studied. However, endothelin signaling also plays crucial roles in the development of neural crest cell-derived tissues. Mechanisms of endothelin action during neural crest cell maturation have been deciphered using a variety of in vivo and in vitro approaches, with these studies elucidating the basis of human syndromes involving developmental differences resulting from altered endothelin signaling. In this Review, we describe the endothelin pathway and its functions during the development of neural crest-derived tissues. We also summarize how dysregulated endothelin signaling causes developmental differences and how this knowledge may lead to potential treatments for individuals with gene variants in the endothelin pathway.

Mutations in genes related to myocyte contraction and ventricular septum development in non-syndromic tetralogy of Fallot

Objective

Eighty percent of patients with a diagnosis of tetralogy of Fallot (TOF) do not have a known genetic etiology or syndrome. We sought to identify key molecular pathways and biological processes that are enriched in non-syndromic TOF, the most common form of cyanotic congenital heart disease, rather than single driver genes to elucidate the pathogenesis of this disease.

Methods

We undertook exome sequencing of 362 probands with non-syndromic TOF and their parents within the Pediatric Cardiac Genomics Consortium (PCGC). We identified rare (minor allele frequency <1 × 10-4), de novo variants to ascertain pathways and processes affected in this population to better understand TOF pathogenesis. Pathways and biological processes enriched in the PCGC TOF cohort were compared to 317 controls without heart defects (and their parents) from the Simons Foundation Autism Research Initiative (SFARI).

Results

A total of 120 variants in 117 genes were identified as most likely to be deleterious, with CHD7, CLUH, UNC13C, and WASHC5 identified in two probands each. Gene ontology analyses of these variants using multiple bioinformatic tools demonstrated significant enrichment in processes including cell cycle progression, chromatin remodeling, myocyte contraction and calcium transport, and development of the ventricular septum and ventricle. There was also a significant enrichment of target genes of SOX9, which is critical in second heart field development and whose loss results in membranous ventricular septal defects related to disruption of the proximal outlet septum. None of these processes was significantly enriched in the SFARI control cohort.

Conclusion

Innate molecular defects in cardiac progenitor cells and genes related to their viability and contractile function appear central to non-syndromic TOF pathogenesis. Future research utilizing our results is likely to have significant implications in stratification of TOF patients and delivery of personalized clinical care.

The heart field transcriptional landscape at single-cell resolution

Organogenesis requires the orchestrated development of multiple cell lineages that converge, interact, and specialize to generate coherent functional structures, exemplified by transformation of the cardiac crescent into a four-chambered heart. Cardiomyocytes originate from the first and second heart fields, which make different regional contributions to the definitive heart. In this review, a series of recent single-cell transcriptomic analyses, together with genetic tracing experiments, are discussed, providing a detailed panorama of the cardiac progenitor cell landscape. These studies reveal that first heart field cells originate in a juxtacardiac field adjacent to extraembryonic mesoderm and contribute to the ventrolateral side of the cardiac primordium. In contrast, second heart field cells are deployed dorsomedially from a multilineage-primed progenitor population via arterial and venous pole pathways. Refining our knowledge of the origin and developmental trajectories of cells that build the heart is essential to address outstanding challenges in cardiac biology and disease.

Cholecystokinin peptide signaling is regulated by a TBX5-MEF2 axis in the heart

The procholecystokinin (proCCK) gene encodes a secreted peptide known to regulate the digestive, endocrine, and nervous systems. Though recently proposed as a biomarker for heart dysfunction, its physiological role in both the embryonic and adult heart is poorly understood, and there are no reports of tissue-specific regulators of cholecystokinin signaling in the heart or other tissues. In the present study, mRNA of proCCK was observed in cardiac tissues during mouse embryonic development, establishing proCCK as an early marker of differentiated cardiomyocytes which is later restricted to anatomical subdomains of the neonatal heart. Three-dimensional analysis of the expression of proCCK and CCKAR/CCKBR receptors was performed using in situ hybridization and optical projection tomography, illustrating chamber-specific expression patterns in the postnatal heart. Transcription factor motif analyses indicated developmental cardiac transcription factors TBX5 and MEF2C as upstream regulators of proCCK, and this regulatory activity was confirmed in reporter gene assays. proCCK mRNA levels were also measured in the infarcted heart and in response to cyclic mechanical stretch and endothelin-1, indicating dynamic transcriptional regulation which might be leveraged for improved biomarker development. Functional analyses of exogenous cholecystokinin octapeptide (CCK-8) administration were performed in differentiating mouse embryonic stem cells (mESCs), and the results suggest that CCK-8 does not act as a differentiation modulator of cardiomyocyte subtypes. Collectively, these findings indicate that proCCK is regulated at the transcriptional level by TBX5-MEF2 and neurohormonal signaling, informing use of proCCK as a biomarker and future strategies for upstream manipulation of cholecystokinin signaling in the heart and other tissues.

Evolution of the endothelin pathway drove neural crest cell diversification

Neural crest cells (NCCs) are migratory, multipotent embryonic cells that are unique to vertebrates and form an array of clade-defining adult features. The evolution of NCCs has been linked to various genomic events, including the evolution of new gene-regulatory networks^1,2, the de novo evolution of genes³ and the proliferation of paralogous genes during genome-wide duplication events⁴. However, conclusive functional evidence linking new and/or duplicated genes to NCC evolution is lacking. Endothelin ligands (Edns) and endothelin receptors (Ednrs) are unique to vertebrates^3,5,6, and regulate multiple aspects of NCC development in jawed vertebrates^7-10. Here, to test whether the evolution of Edn signalling was a driver of NCC evolution, we used CRISPR-Cas9 mutagenesis¹¹ to disrupt edn, ednr and dlx genes in the sea lamprey, Petromyzon marinus. Lampreys are jawless fishes that last shared a common ancestor with modern jawed vertebrates around 500 million years ago¹². Thus, comparisons between lampreys and gnathostomes can identify deeply conserved and evolutionarily flexible features of vertebrate development. Using the frog Xenopus laevis to expand gnathostome phylogenetic representation and facilitate side-by-side analyses, we identify ancient and lineage-specific roles for Edn signalling. These findings suggest that Edn signalling was activated in NCCs before duplication of the vertebrate genome. Then, after one or more genome-wide duplications in the vertebrate stem, paralogous Edn pathways functionally diverged, resulting in NCC subpopulations with different Edn signalling requirements. We posit that this new developmental modularity facilitated the independent evolution of NCC derivatives in stem vertebrates. Consistent with this, differences in Edn pathway targets are associated with differences in the oropharyngeal skeleton and autonomic nervous system of lampreys and modern gnathostomes. In summary, our work provides functional genetic evidence linking the origin and duplication of new vertebrate genes with the stepwise evolution of a defining vertebrate novelty.

New markers for regulation of transcription and macromolecule metabolic process in porcine oocytes during in vitro maturation

Oocyte maturation is essential for proper fertilization, embryo implantation and early development. While the physiological conditions of these processes are relatively well-known, its exact molecular mechanisms remain widely undiscovered. Oocyte growth, differentiation and maturation are therefore the subject of scientific debate. Precious literature has indicated that the oocyte itself serves a regulatory role in the mechanisms underlying these processes. Hence, the present study performed expression microarrays to analyze the complete transcriptome of porcine oocytes during their in vitro maturation (IVM). Pig material was used for experimentation, as it possesses similarities to the reproductive processes and general genetic proximities of Sus scrofa to human. Oocytes, isolated from the ovaries of slaughtered animals were assessed via the Brilliant Cresyl Blue test and directed to IVM. A number of oocytes were left to be analyzed as the ‘before IVM’ group. Oocyte mRNA was isolated and used for microarray analysis, which was subsequently validated via RT-qPCR. The current study particularly focused on genes belonging to ‘positive regulation of transcription, DNA-dependent’, ‘positive regulation of gene expression’, ‘positive regulation of macromolecule metabolic process’ and ‘positive regulation of transcription from RNA polymerase II promoter’ ontologies. FOS, VEGFA, ESR1, AR, CCND2, EGR2, ENDRA, GJA1, INHBA, IHH, INSR, APP, WWTR1, SMARCA1, NFAT5, SMAD4, MAP3K1, EGR1, RORA, ECE1, NR5A1, KIT, IKZF2, MEF2C, SH3D19, MITF and PSMB4 were all determined to be significantly altered (fold change, >|2|; P<0.05) among these groups, with their downregulation being observed after IVM. Genes with the most altered expressions were analyzed and considered to be potential markers of maturation associated with transcription regulation and macromolecule metabolism process.

Epigenetics and Mechanobiology in Heart Development and Congenital Heart Disease

: Congenital heart disease (CHD) is the most common birth defect worldwide and the number one killer of live-born infants in the United States. Heart development occurs early in embryogenesis and involves complex interactions between multiple cell populations, limiting the understanding and consequent treatment of CHD. Furthermore, genome sequencing has largely failed to predict or yield therapeutics for CHD. In addition to the underlying genome, epigenetics and mechanobiology both drive heart development. A growing body of evidence implicates the aberrant regulation of these two extra-genomic systems in the pathogenesis of CHD. In this review, we describe the stages of human heart development and the heart defects known to manifest at each stage. Next, we discuss the distinct and overlapping roles of epigenetics and mechanobiology in normal development and in the pathogenesis of CHD. Finally, we highlight recent advances in the identification of novel epigenetic biomarkers and environmental risk factors that may be useful for improved diagnosis and further elucidation of CHD etiology.

Promoter interactome of human embryonic stem cell-derived cardiomyocytes connects GWAS regions to cardiac gene networks

Long-range chromosomal interactions bring distal regulatory elements and promoters together to regulate gene expression in biological processes. By performing promoter capture Hi-C (PCHi-C) on human embryonic stem cell-derived cardiomyocytes (hESC-CMs), we show that such promoter interactions are a key mechanism by which enhancers contact their target genes after hESC-CM differentiation from hESCs. We also show that the promoter interactome of hESC-CMs is associated with expression quantitative trait loci (eQTLs) in cardiac left ventricular tissue; captures the dynamic process of genome reorganisation after hESC-CM differentiation; overlaps genome-wide association study (GWAS) regions associated with heart rate; and identifies new candidate genes in such regions. These findings indicate that regulatory elements in hESC-CMs identified by our approach control gene expression involved in ventricular conduction and rhythm of the heart. The study of promoter interactions in other hESC-derived cell types may be of utility in functional investigation of GWAS-associated regions.

Amniogenic somatopleure: a novel origin of multiple cell lineages contributing to the cardiovascular system

The somatopleure is the amniotic primordium in amniote development, but its boundary to the embryonic body at early embryonic stages and the fate of cells constituting this structure are not well characterized. It also remains unclear how cells behave during the demarcation between intra- and extra-embryonic tissues. Here we identify cellular alignments, which indicate two streams towards the sites of dorsal amniotic closure and ventral thoracic wall formation. A subpopulation of mesodermal cells moving ventrally from the somatopleural region adjacent to the base of the head fold enter the body of the embryo and distribute to the thoracic wall, pharyngeal arches and heart. These cells are induced to differentiate into vascular endothelial cells and cardiomyocytes possibly by FGF and BMP signaling, respectively. These results indicate that the somatopleure acting as the amniotic primordium also serves as a source of embryonic cells, which may contribute to cardiovascular development.

Sfrp5 identifies murine cardiac progenitors for all myocardial structures except for the right ventricle

Upon acquirement of pulmonary circulation, the ancestral heart may have been remodelled coincidently with, or accompanied by, the production and rearrangement of progenitor cells. However, the progenitor populations that give rise to the left ventricle (LV) and sinus venosus (SV) are still ambiguous. Here we show that the expression of Secreted frizzled-related protein Sfrp5 in the mouse identifies common progenitors for the outflow tract (OFT), LV, atrium and SV but not the right ventricle (RV). Sfrp5 expression begins at the lateral sides of the cardiac crescent, excluding early differentiating regions, and continues in the venous pole, which gives rise to the SV. Lineage-tracing analysis revealed that descendants of Sfrp5-expressing cells at E7.5 contribute not only to the SV but also to the LV, atria and OFT and are found also in the dorsal splanchnic mesoderm accompanied by the expression of the secondary heart field marker, Islet1. These findings provide insight into the arrangement of cardiac progenitors for systemic circulation.

It is unclear which progenitors define different regions of the heart. Here, the authors find Secreted frizzled-related protein 5 is expressed in murine progenitor cells for the outflow tract, first heart field, and sinus venosus, but not the right ventricle, and Wnt inhibition prevents progenitor proliferation.

Postotic and preotic cranial neural crest cells differently contribute to thyroid development

Thyroid development and formation vary among species, but in most species the thyroid morphogenesis consists of five stages: specification, budding, descent, bilobation and folliculogenesis. The detailed mechanisms of these stages have not been fully clarified. During early development, the cranial neural crest (CNC) contributes to the thyroid gland. The removal of the postotic CNC (corresponding to rhombomeres 6, 7 and 8, also known as the cardiac neural crest) results in abnormalities of the cardiovascular system, thymus, parathyroid glands, and thyroid gland. To investigate the influence of the CNC on thyroid bilobation process, we divided the CNC into two regions, the postotic CNC and the preotic CNC (from the mesencephalon to rhombomere 5) regions and examined. We found that preotic CNC-ablated embryos had a unilateral thyroid lobe, and confirmed the presence of a single lobe or the absence of lobes in postotic CNC-ablated chick embryos. The thyroid anlage in each region-ablated embryos was of a normal size at the descent stage, but at a later stage, the thyroid in preotic CNC-ablated embryos was of a normal size, conflicting with a previous report in which the thyroid was reduced in size in the postotic CNC-ablated embryos. The postotic CNC cells differentiated into connective tissues of the thyroid in quail-to-chick chimeras. In contrast, the preotic CNC cells did not differentiate into connective tissues of the thyroid. We found that preotic CNC cells encompassed the thyroid anlage from the specification stage to the descent stage. Finally, we found that endothelin-1 and endothelin type A receptor-knockout mice and bosentan (endothelin receptor antagonist)-treated chick embryos showed bilobation anomalies that included single-lobe formation. Therefore, not only the postotic CNC, but also the preotic CNC plays an important role in thyroid morphogenesis.

Association analysis identifies new risk loci for congenital heart disease in Chinese populations

Our previous genome-wide association study (GWAS) identified two susceptibility loci for congenital heart disease (CHD) in Han Chinese. Here we identify additional loci by testing promising associations in an extended 3-stage validation consisting of 6,053 CHD cases and 7,410 controls. We find GW significant (P<5.0 × 10(-8)) evidence of 4 additional CHD susceptibility loci at 4q31.22 (rs1400558, upstream of EDNRA, Pall=1.63 × 10(-9)), 9p24.2 (rs7863990, close to SMARCA2, Pall=3.71 × 10(-14)), 12q24.13 (rs2433752, upstream of TBX3 and TBX5, Pall=1.04 × 10(-10)) and 20q12 (rs490514, in PTPRT, Pall=1.20 × 10(-13)). Moreover, the data from previous European GWAS supports that rs490514 is associated with the risk of CHD (P=3.40 × 10(-3)). These results enhance our understanding of CHD susceptibility.

Developmental genetic bases behind the independent origin of the tympanic membrane in mammals and diapsids

The amniote middle ear is a classical example of the evolutionary novelty. Although paleontological evidence supports the view that mammals and diapsids (modern reptiles and birds) independently acquired the middle ear after divergence from their common ancestor, the developmental bases of these transformations remain unknown. Here we show that lower-to-upper jaw transformation induced by inactivation of the Endothelin1-Dlx5/6 cascade involving Goosecoid results in loss of the tympanic membrane in mouse, but causes duplication of the tympanic membrane in chicken. Detailed anatomical analysis indicates that the relative positions of the primary jaw joint and first pharyngeal pouch led to the coupling of tympanic membrane formation with the lower jaw in mammals, but with the upper jaw in diapsids. We propose that differences in connection and release by various pharyngeal skeletal elements resulted in structural diversity, leading to the acquisition of the tympanic membrane in two distinct manners during amniote evolution.

The evolution of the amniote middle ear remains unclear. Here, the authors show that inactivation of the Edn1-Dlx5/6 cascade during development results in loss of the tympanic membrane in mouse and duplication in chicken, which suggests independent evolution of the tympanic membrane in different amniotes.

Distinct effects of Hoxa2 overexpression in cranial neural crest populations reveal that the mammalian hyomandibular-ceratohyal boundary maps within the styloid process

Most gnathostomata craniofacial structures derive from pharyngeal arches (PAs), which are colonized by cranial neural crest cells (CNCCs). The anteroposterior and dorsoventral identities of CNCCs are defined by the combinatorial expression of Hox and Dlx genes. The mechanisms associating characteristic Hox/Dlx expression patterns with the topology and morphology of PAs derivatives are only partially known; a better knowledge of these processes might lead to new concepts on the origin of taxon-specific craniofacial morphologies and of certain craniofacial malformations. Here we show that ectopic expression of Hoxa2 in Hox-negative CNCCs results in distinct phenotypes in different CNCC subpopulations. Namely, while ectopic Hoxa2 expression is sufficient for the morphological and molecular transformation of the first PA (PA1) CNCC derivatives into the second PA (PA2)-like structures, this same genetic alteration does not provoke the transformation of derivatives of other CNCC subpopulations, but severely impairs their development. Ectopic Hoxa2 expression results in the transformation of the proximal Meckel's cartilage and of the malleus, two ventral PA1 CNCCs derivatives, into a supernumerary styloid process (SP), a PA2-derived mammalian-specific skeletal structure. These results, together with experiments to inactivate and ectopically activate the Edn1-Dlx5/6 pathway, indicate a dorsoventral PA2 (hyomandibular/ceratohyal) boundary passing through the middle of the SP. The present findings suggest context-dependent function of Hoxa2 in CNCC regional specification and morphogenesis, and provide novel insights into the evolution of taxa-specific patterning of PA-derived structures.

Evolution of endothelin receptors in vertebrates

Endothelin receptors are G protein coupled receptors (GPCRs) of the β-group of rhodopsin receptors that bind to endothelin ligands, which are 21 amino acid long peptides derived from longer prepro-endothelin precursors. The most basal Ednr-like GPCR is found outside vertebrates in the cephalochordate amphioxus, but endothelin ligands are only present among vertebrates, including the lineages of jawless vertebrates (lampreys and hagfishes), cartilaginous vertebrates (sharks, rays, and chimaeras), and bony vertebrates (ray-finned fishes and lobe-finned vertebrates including tetrapods). A bona fide endothelin system is thus a vertebrate-specific innovation with important roles for regulating the cardiovascular system, renal and pulmonary processes, as well as for the development of the vertebrate-specific neural crest cell population and its derivatives. Expectedly, dysregulation of endothelin receptors and the endothelin system leads to a multitude of human diseases. Despite the importance of different types of endothelin receptors for vertebrate development and physiology, current knowledge on endothelin ligand-receptor interactions, on the expression of endothelin receptors and their ligands, and on the functional roles of the endothelin system for embryonic development and in adult vertebrates is very much biased towards amniote vertebrates. Recent analyses from a variety of vertebrate lineages, however, have shown that the endothelin system in lineages such as teleost fish and lampreys is more diverse and is divergent from the mammalian endothelin system. This diversity is mainly based on differential evolution of numerous endothelin system components among vertebrate lineages generated by two rounds of whole genome duplication (three in teleosts) during vertebrate evolution. Here we review current understanding of the evolutionary history of the endothelin receptor family in vertebrates supplemented with surveys on the endothelin receptor gene complement of newly available genome assemblies from phylogenetically informative taxa. Our assessment further highlights the diversity of the vertebrate endothelin system and calls for detailed functional and pharmacological analyses of the endothelin system beyond tetrapods.

Specification of the mouse cardiac conduction system in the absence of Endothelin signaling

Coordinated contraction of the heart is essential for survival and is regulated by the cardiac conduction system. Contraction of ventricular myocytes is controlled by the terminal part of the conduction system known as the Purkinje fiber network. Lineage analyses in chickens and mice have established that the Purkinje fibers of the peripheral ventricular conduction system arise from working myocytes during cardiac development. It has been proposed, based primarily on gain-of-function studies, that Endothelin signaling is responsible for myocyte-to-Purkinje fiber transdifferentiation during avian heart development. However, the role of Endothelin signaling in mammalian conduction system development is less clear, and the development of the cardiac conduction system in mice lacking Endothelin signaling has not been previously addressed. Here, we assessed the specification of the cardiac conduction system in mouse embryos lacking all Endothelin signaling. We found that mouse embryos that were homozygous null for both ednra and ednrb, the genes encoding the two Endothelin receptors in mice, were born at predicted Mendelian frequency and had normal specification of the cardiac conduction system and apparently normal electrocardiograms with normal QRS intervals. In addition, we found that ednra expression within the heart was restricted to the myocardium while ednrb expression in the heart was restricted to the endocardium and coronary endothelium. By establishing that ednra and ednrb are expressed in distinct compartments within the developing mammalian heart and that Endothelin signaling is dispensable for specification and function of the cardiac conduction system, this work has important implications for our understanding of mammalian cardiac development.

Endothelin-1 signalling controls early embryonic heart rate in vitro and in vivo

AIM

Spontaneous activity of embryonic cardiomyocytes originates from sarcoplasmic reticulum (SR) Ca(2+) release during early cardiogenesis. However, the regulation of heart rate during embryonic development is still not clear. The aim of this study was to determine how endothelin-1 (ET-1) affects the heart rate of embryonic mice, as well as the pathway through which it exerts its effects.

METHODS

The effects of ET-1 and ET-1 receptor inhibition on cardiac contraction were studied using confocal Ca(2+) imaging of isolated mouse embryonic ventricular cardiomyocytes and ultrasonographic examination of embryonic cardiac contractions in utero. In addition, the amount of ET-1 peptide and ET receptor a (ETa) and b (ETb) mRNA levels were measured during different stages of development of the cardiac muscle.

RESULTS

High ET-1 concentration and expression of both ETa and ETb receptors was observed in early cardiac tissue. ET-1 was found to increase the frequency of spontaneous Ca(2+) oscillations in E10.5 embryonic cardiomyocytes in vitro. Non-specific inhibition of ET receptors with tezosentan caused arrhythmia and bradycardia in isolated embryonic cardiomyocytes and in whole embryonic hearts both in vitro (E10.5) and in utero (E12.5). ET-1-mediated stimulation of early heart rate was found to occur via ETb receptors and subsequent inositol trisphosphate receptor activation and increased SR Ca(2+) leak.

CONCLUSION

Endothelin-1 is required to maintain a sufficient heart rate, as well as to prevent arrhythmia during early development of the mouse heart. This is achieved through ETb receptor, which stimulates Ca(2+) leak through IP3 receptors.

Endothelin regulates neural crest deployment and fate to form great vessels through Dlx5/Dlx6-independent mechanisms

Endothelin-1 (Edn1), originally identified as a vasoconstrictor peptide, is involved in the development of cranial/cardiac neural crest-derived tissues and organs. In craniofacial development, Edn1 binds to Endothelin type-A receptor (Ednra) to induce homeobox genes Dlx5/Dlx6 and determines the mandibular identity in the first pharyngeal arch. However, it remains unsolved whether this pathway is also critical for pharyngeal arch artery development to form thoracic arteries. Here, we show that the Edn1/Ednra signaling is involved in pharyngeal artery development by controlling the fate of neural crest cells through a Dlx5/Dlx6-independent mechanism. Edn1 and Ednra knock-out mice demonstrate abnormalities in pharyngeal arch artery patterning, which include persistent first and second pharyngeal arteries, resulting in additional branches from common carotid arteries. Neural crest cell labeling with Wnt1-Cre transgene and immunostaining for smooth muscle cell markers revealed that neural crest cells abnormally differentiate into smooth muscle cells at the first and second pharyngeal arteries of Ednra knock-out embryos. By contrast, Dlx5/Dlx6 knockout little affect the development of pharyngeal arch arteries and coronary arteries, the latter of which is also contributed by neural crest cells through an Edn-dependent mechanism. These findings indicate that the Edn1/Ednra signaling regulates neural crest differentiation to ensure the proper patterning of pharyngeal arch arteries, which is independent of the regional identification of the pharyngeal arches along the dorsoventral axis mediated by Dlx5/Dlx6.

Preotic neural crest cells contribute to coronary artery smooth muscle involving endothelin signalling

Neural crest cells constitute a multipotent cell population that gives rise to diverse cell lineages. The neural crest arising from the postotic hindbrain is known as the 'cardiac' neural crest, and contributes to the great vessels and outflow tract endocardial cushions, but the neural crest contribution to structures within the heart remains largely controversial. Here we demonstrate that neural crest cells from the preotic region migrate into the heart and differentiate into coronary artery smooth muscle cells. Preotic neural crest cells preferentially distribute to the conotruncal region and interventricular septum. Ablation of the preotic neural crest causes abnormalities in coronary septal branch and orifice formation. Mice and chicks lacking endothelin signalling show similar abnormalities in the coronary artery, indicating its involvement in neural crest-dependent coronary artery formation. This is the first report that reveals the preotic neural crest contribution to heart development and smooth muscle heterogeneity within a coronary artery.

Endothelin-1 stimulates the expression of L-type Ca2+ channels in neonatal rat cardiomyocytes via the extracellular signal-regulated kinase 1/2 pathway

The cardiac L-type Ca(2+) channel current (I(Ca,L)) plays an important role in controlling both cardiac excitability and excitation-contraction coupling and is involved in the electrical remodeling during postnatal heart development and cardiac hypertrophy. However, the possible role of endothelin-1 (ET-1) in the electrical remodeling of postnatal and diseased hearts remains unclear. Therefore, the present study was designed to investigate the transcriptional regulation of I(Ca,L) mediated by ET-1 in neonatal rat ventricular myocytes using the whole-cell patch-clamp technique, quantitative RT-PCR and Western blotting. Furthermore, we determined whether the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway is involved. ET-1 increased I(Ca,L) density without altering its voltage dependence of activation and inactivation. In line with the absence of functional changes, ET-1 increased L-type Ca(2+) channel pore-forming α1C-subunit mRNA and protein levels without affecting the mRNA expression of auxiliary β- and α2/δ-subunits. Furthermore, an actinomycin D chase experiment revealed that ET-1 did not alter α1C-subunit mRNA stability. These effects of ET-1 were inhibited by the ETA receptor antagonist BQ-123 but not the ETB receptor antagonist BQ-788. Moreover, the effects of ET-1 on I(Ca,L) and α1C-subunit expression were abolished by the ERK1/2 inhibitor (PD98059) but not by the p38 MAPK inhibitor (SB203580) or the c-Jun N-terminal kinase inhibitor (SP600125). These findings indicate that ET-1 increased the transcription of L-type Ca(2+) channel in cardiomyocytes via activation of ERK1/2 through the ETA receptor, which may contribute to the electrical remodeling of heart during postnatal development and cardiac hypertrophy.

Angiogenic morphogenesis driven by dynamic and heterogeneous collective endothelial cell movement

Angiogenesis is a complex process, which is accomplished by reiteration of modules such as sprouting, elongation and bifurcation, that configures branching vascular networks. However, details of the individual and collective behaviors of vascular endothelial cells (ECs) during angiogenic morphogenesis remain largely unknown. Herein, we established a time-lapse imaging and computer-assisted analysis system that quantitatively characterizes behaviors in sprouting angiogenesis. Surprisingly, ECs moved backwards and forwards, overtaking each other even at the tip, showing an unknown mode of collective cell movement with dynamic ‘cell-mixing’. Mosaic analysis, which enabled us to monitor the behavior of individual cells in a multicellular structure, confirmed the ‘cell-mixing’ phenomenon of ECs that occurs at the whole-cell level. Furthermore, an in vivo EC-tracking analysis revealed evidence of cell-mixing and overtaking at the tip in developing murine retinal vessels. In parametrical analysis, VEGF enhanced tip cell behavior and directed EC migration at the stalk during branch elongation. These movements were counter-regulated by EC-EC interplay via γ-secretase-dependent Dll4-Notch signaling, and might be promoted by EC-mural cell interplay. Finally, multiple regression analysis showed that these molecule-mediated tip cell behaviors and directed EC migration contributed to effective branch elongation. Taken together, our findings provide new insights into the individual and collective EC movements driving angiogenic morphogenesis. The methodology used for this analysis might serve to bridge the gap in our understanding between individual cell behavior and branching morphogenesis.

Myocyte proliferation in the developing heart

Regulation of organ growth is critical during embryogenesis. At the cellular level, mechanisms controlling the size of individual embryonic organs include cell proliferation, differentiation, migration, and attrition through cell death. All these mechanisms play a role in cardiac morphogenesis, but experimental studies have shown that the major determinant of cardiac size during prenatal development is myocyte proliferation. As this proliferative capacity becomes severely restricted after birth, the number of cell divisions that occur during embryogenesis limits the growth potential of the postnatal heart. We summarize here current knowledge concerning regional control of myocyte proliferation as related to cardiac morphogenesis and dysmorphogenesis. There are significant spatial and temporal differences in rates of cell division, peaking during the preseptation period and then gradually decreasing toward birth. Analysis of regional rates of proliferation helps to explain the mechanics of ventricular septation, chamber morphogenesis, and the development of the cardiac conduction system. Proliferation rates are influenced by hemodynamic loading, and transduced by autocrine and paracrine signaling by means of growth factors. Understanding the biological response of the developing heart to such factors and physical forces will further our progress in engineering artificial myocardial tissues for heart repair and designing optimal treatment strategies for congenital heart disease.

Origin and development of the atrioventricular myocardial lineage: insight into the development of accessory pathways

Defects originating from the atrioventricular canal region are part of a wide spectrum of congenital cardiovascular malformations that frequently affect newborns. These defects include partial or complete atrioventricular septal defects, atrioventricular valve defects, and arrhythmias, such as atrioventricular re-entry tachycardia, atrioventricular nodal block, and ventricular preexcitation. Insight into the cellular origin of the atrioventricular canal myocardium and the molecular mechanisms that control its development will aid in the understanding of the etiology of the atrioventricular defects. This review discusses current knowledge concerning the origin and fate of the atrioventricular canal myocardium, the molecular mechanisms that determine its specification and differentiation, and its role in the development of certain malformations such as those that underlie ventricular preexcitation.

Identification and developmental analysis of endothelin receptor type-A expressing cells in the mouse kidney

The endothelin (Edn) system plays pleiotropic roles in renal function and various disease processes through two distinct G protein-coupled receptors, Edn receptors type-A (Ednra) and type-B (Ednrb). However, difficulties in the accurate identification of receptor-expressing cells in situ have made it difficult to dissect their diverse action in renal (patho)physiology. We have recently established mouse lines in which lacZ and EGFP are 'knocked-in' to the Ednra locus to faithfully mark Ednra-expressing cells. Here we analyzed these mice for their expression in the kidney to characterize Ednra-expressing cells. Ednra expression was first observed in undifferentiated mesenchymal cells around the ureteric bud at E12.5. Thereafter, Ednra expression was widely observed in vascular smooth muscle cells, JG cells and mesenchymal cells in the interstitium. After growth, the expression became confined to vascular smooth muscle cells, pericytes and renin-producing JG cells. By contrast, most cells in the nephron and vascular endothelial cells did not express Ednra. These results indicate that Ednra expression may be linked with non-epithelial fate determination and differentiation of metanephric mesenchyme. Ednra-lacZ/EGFP knock-in mice may serve as a useful tool in studies on renal function and pathophysiology of various renal diseases.