The heart tube forms and elongates through dynamic cell rearrangement coordinated with foregut extension.

In the initiation of cardiogenesis, the heart primordia transform from bilateral flat sheets of mesoderm into an elongated midline tube. Here, we discover that this rapid architectural change is driven by actomyosin-based oriented cell rearrangement and resulting dynamic tissue reshaping (convergent extension, CE). By labeling clusters of cells spanning the entire heart primordia, we show that the heart primordia converge toward the midline to form a narrow tube, while extending perpendicularly to rapidly lengthen it. Our data for the first time visualize the process of early heart tube formation from both the medial (second) and lateral (first) heart fields, revealing that both fields form the early heart tube by essentially the same mechanism. Additionally, the adjacent endoderm coordinately forms the foregut through previously unrecognized movements that parallel those of the heart mesoderm and elongates by CE. In conclusion, our data illustrate how initially two-dimensional flat primordia rapidly change their shapes and construct the three-dimensional morphology of emerging organs in coordination with neighboring morphogenesis.

Understanding Heart Field Progenitor Cells for Modeling Congenital Heart Diseases.

PURPOSE OF REVIEW: Heart development is a meticulously coordinated process that involves the specification of two distinct populations of cardiac progenitor cells, namely the first and the second heart field. Disruption of heart field progenitors can result in congenital heart defects. In this review, we aim to describe the signaling pathways and transcription factors that link heart field development and congenital heart disease. RECENT FINDINGS: Single-cell transcriptomics, lineage-tracing mouse models, and stem cell-based in vitro modeling of cardiogenesis have significantly improved the spatiotemporal characterization of cardiac progenitors. Additionally, novel functional genomic studies have now linked more genetic variants with congenital heart disease. Dysregulation of cardiac progenitor cells causes malformations that can be lethal. Ongoing research will continue to shed light on cardiac morphogenesis and help us better understand and treat patients with congenital heart disease.

The functional diversity of essential genes required for mammalian cardiac development.

Genes required for an organism to develop to maturity (for which no other gene can compensate) are considered essential. The continuing functional annotation of the mouse genome has enabled the identification of many essential genes required for specific developmental processes including cardiac development. Patterns are now emerging regarding the functional nature of genes required at specific points throughout gestation. Essential genes required for development beyond cardiac progenitor cell migration and induction include a small and functionally homogenous group encoding transcription factors, ligands and receptors. Actions of core cardiogenic transcription factors from the Gata, Nkx, Mef, Hand, and Tbx families trigger a marked expansion in the functional diversity of essential genes from midgestation onwards. As the embryo grows in size and complexity, genes required to maintain a functional heartbeat and to provide muscular strength and regulate blood flow are well represented. These essential genes regulate further specialization and polarization of cell types along with proliferative, migratory, adhesive, contractile, and structural processes. The identification of patterns regarding the functional nature of essential genes across numerous developmental systems may aid prediction of further essential genes and those important to development and/or progression of disease.

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.

Normal development of the heart: a review of new findings.

Development and formation of the heart, the central organ of the circulatory system in vertebrates, starts early during embryonic development (second week), reaching maturity during the first few postnatal months. Cardiogenesis is a highly complex process that requires the active and orderly participation of different cardiac and non-cardiac cell populations. Thus, this process is sensitive to errors that may trigger a variety of heart-development defects, called congenital heart defects, which have a worldwide incidence of 8-10/1000 live births. A good understanding of normal cardiogenesis is required for better diagnosis and treatment of congenital heart diseases. This article reviews normal cardiogenesis by comparing information from classic studies with more recent findings. Information from descriptive anatomical studies of histological sections and selective in vivo marking of chicken embryos were emphasized. In addition, the discovery of heart fields has fueled the investigation of cardiogenic events that were believed to be understood and has contributed to proposals for new models of heart development.

El corazón, órgano central del aparato circulatorio de los vertebrados, comienza a formarse muy temprano en el desarrollo embrionario (segunda semana de gestación) y alcanza su forma madura durante los primeros meses posteriores al nacimiento. La cardiogénesis se caracteriza por ser un proceso altamente complejo, dependiente de la participación activa y ordenada de diferentes poblaciones celulares cardiacas y no cardiacas. Lo anterior hace que este proceso sea sensible a errores que pueden desencadenar una variedad de defectos del desarrollo cardiaco, llamados cardiopatías congénitas, con una incidencia mundial de 8 a 10/1000 nacidos vivos. Para mejorar el diagnóstico y el tratamiento de las cardiopatías congénitas es necesario comprender adecuadamente los eventos implicados en la cardiogénesis normal. En este artículo se revisa el desarrollo cardiaco normal, contrastando la información de los estudios clásicos con la de hallazgos recientes. Se hace hincapié en la información obtenida de los estudios de anatomía descriptiva de cortes histológicos y marcaje selectivo in vivo en embriones de pollo. Adicionalmente, el descubrimiento de los campos cardiogénicos ha estimulado la investigación de eventos cardiogénicos que se creían comprendidos, contribuyendo con propuestas de nuevos modelos del desarrollo del corazón.

Transcriptional, Electrophysiological, and Metabolic Characterizations of hESC-Derived First and Second Heart Fields Demonstrate a Potential Role of TBX5 in Cardiomyocyte Maturation.

Background: Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) can be used as a source for cell delivery to remuscularize the heart after myocardial infarction. Despite their therapeutic potential, the emergence of ventricular arrhythmias has limited their application. We previously developed a double reporter hESC line to isolate first heart field (FHF: TBX5 + NKX2-5 +) and second heart field (SHF: TBX5 - NKX2-5 + ) CMs. Herein, we explore the role of TBX5 and its effects on underlying gene regulatory networks driving phenotypical and functional differences between these two populations. Methods: We used a combination of tools and techniques for rapid and unsupervised profiling of FHF and SHF populations at the transcriptional, translational, and functional level including single cell RNA (scRNA) and bulk RNA sequencing, atomic force and quantitative phase microscopy, respirometry, and electrophysiology. Results: Gene ontology analysis revealed three biological processes attributed to TBX5 expression: sarcomeric structure, oxidative phosphorylation, and calcium ion handling. Interestingly, migratory pathways were enriched in SHF population. SHF-like CMs display less sarcomeric organization compared to FHF-like CMs, despite prolonged in vitro culture. Atomic force and quantitative phase microscopy showed increased cellular stiffness and decreased mass distribution over time in FHF compared to SHF populations, respectively. Electrophysiological studies showed longer plateau in action potentials recorded from FHF-like CMs, consistent with their increased expression of calcium handling genes. Interestingly, both populations showed nearly identical respiratory profiles with the only significant functional difference being higher ATP generation-linked oxygen consumption rate in FHF-like CMs. Our findings suggest that FHF-like CMs display more mature features given their enhanced sarcomeric alignment, calcium handling, and decreased migratory characteristics. Finally, pseudotime analyses revealed a closer association of the FHF population to human fetal CMs along the developmental trajectory. Conclusion: Our studies reveal that distinguishing FHF and SHF populations based on TBX5 expression leads to a significant impact on their downstream functional properties. FHF CMs display more mature characteristics such as enhanced sarcomeric organization and improved calcium handling, with closer positioning along the differentiation trajectory to human fetal hearts. These data suggest that the FHF CMs may be a more suitable candidate for cardiac regeneration.

Normal development of the heart: a review of new findings / Desarrollo normal del corazón: revisión de nuevos hallazgos

Abstract Development and formation of the heart, the central organ of the circulatory system in vertebrates, starts early during embryonic development (second week), reaching maturity during the first few postnatal months. Cardiogenesis is a highly complex process that requires the active and orderly participation of different cardiac and non-cardiac cell populations. Thus, this process is sensitive to errors that may trigger a variety of heart-development defects, called congenital heart defects, which have a worldwide incidence of 8-10/1000 live births. A good understanding of normal cardiogenesis is required for better diagnosis and treatment of congenital heart diseases. This article reviews normal cardiogenesis by comparing information from classic studies with more recent findings. Information from descriptive anatomical studies of histological sections and selective in vivo marking of chicken embryos were emphasized. In addition, the discovery of heart fields has fueled the investigation of cardiogenic events that were believed to be understood and has contributed to proposals for new models of heart development.

Resumen El corazón, órgano central del aparato circulatorio de los vertebrados, comienza a formarse muy temprano en el desarrollo embrionario (segunda semana de gestación) y alcanza su forma madura durante los primeros meses posteriores al nacimiento. La cardiogénesis se caracteriza por ser un proceso altamente complejo, dependiente de la participación activa y ordenada de diferentes poblaciones celulares cardiacas y no cardiacas. Lo anterior hace que este proceso sea sensible a errores que pueden desencadenar una variedad de defectos del desarrollo cardiaco, llamados cardiopatías congénitas, con una incidencia mundial de 8 a 10/1000 nacidos vivos. Para mejorar el diagnóstico y el tratamiento de las cardiopatías congénitas es necesario comprender adecuadamente los eventos implicados en la cardiogénesis normal. En este artículo se revisa el desarrollo cardiaco normal, contrastando la información de los estudios clásicos con la de hallazgos recientes. Se hace hincapié en la información obtenida de los estudios de anatomía descriptiva de cortes histológicos y marcaje selectivo in vivo en embriones de pollo. Adicionalmente, el descubrimiento de los campos cardiogénicos ha estimulado la investigación de eventos cardiogénicos que se creían comprendidos, contribuyendo con propuestas de nuevos modelos del desarrollo del corazón.

Zrf1 controls mesoderm lineage genes and cardiomyocyte differentiation.

In the present study we addressed the function of the transcriptional activator Zrf1 in the generation of the 3 germ layers during in vitro development. Currently, Zrf1 is rather regarded as a factor that drives the expression of neuronal genes. Here, we have employed mouse embryonic stem cells and P19 cells to understand the role of Zrf1 in the generation of mesoderm-derived tissues like adipocytes, cartilage and heart. Our data shows that Zrf1 is essential for the transcriptional activation of genes that give rise to mesoderm and in particular heart development. In both, the mESC and P19 systems, we provide evidence that Zrf1 contributes to the generation of functional cardiomyocytes. We further demonstrate that Zrf1 binds to the transcription start sites (TSSs) of heart tissue-specific genes from the first and second heart field where it drives their temporal expression during differentiation. Taken together, we have identified Zrf1 as a novel regulator of the mesodermal lineage that might facilitate spatiotemporal expression of genes.

The Early Stages of Heart Development: Insights from Chicken Embryos.

The heart is the first functioning organ in the developing embryo and a detailed understanding of the molecular and cellular mechanisms involved in its formation provides insights into congenital malformations affecting its function and therefore the survival of the organism. Because many developmental mechanisms are highly conserved, it is possible to extrapolate from observations made in invertebrate and vertebrate model organisms to humans. This review will highlight the contributions made through studying heart development in avian embryos, particularly the chicken. The major advantage of chick embryos is their accessibility for surgical manipulation and functional interference approaches, both gain- and loss-of-function. In addition to experiments performed in ovo, the dissection of tissues for ex vivo culture, genomic, or biochemical approaches is straightforward. Furthermore, embryos can be cultured for time-lapse imaging, which enables tracking of fluorescently labeled cells and detailed analysis of tissue morphogenesis. Owing to these features, investigations in chick embryos have led to important discoveries, often complementing genetic studies in mice and zebrafish. As well as including some historical aspects, we cover here some of the crucial advances made in understanding early heart development using the chicken model.

Heart fields: spatial polarity and temporal dynamics.

In chick and mouse, heart fields undergo dynamic morphological spatiotemporal changes during heart tube formation. Here, the dynamic change in spatial polarity of such fields is discussed and a new perspective on the heart fields is proposed. The heart progenitor cells delaminate through the primitive streak and migrate in a semicircular trajectory craniolaterally forming the bilateral heart fields as part of the splanchnic mesoderm. They switch their polarity from anteroposterior to mediolateral. The anterior intestinal portal posterior descent inverts the newly formed heart field mediolateral polarity into lateromedial by 125° bending. The heart fields revert back to their original anteroposterior polarity and fuse at the midline forming a semi heart tube by completing their half circle movement. Several names and roles were assigned to different portions of the heart fields: posterior versus anterior, first versus second, and primary versus secondary heart field. The posterior and anterior heart fields define basically physical fields that form the inflow-outflow axis of the heart tube. The first and second heart fields are, in contrast, temporal fields of differentiating cardiomyocytes expressing myosin light chain 2a and undifferentiated and proliferating precardiac mesoderm expressing Isl1 gene, respectively. The two markers present a complementary pattern and are expressed transiently in all myocardial lineages. Thus, Isl1 is not restricted to a portion of the heart field or one of the two heart lineages as has been often assumed.