Loss of both GATA4 and GATA6 blocks cardiac myocyte differentiation and results in acardia in mice

Targeting GATA6 with pedunculoside inhibits fetal gene expression to attenuate pathological cardiac hypertrophy

BACKGROUND

Pathological cardiac hypertrophy is a characteristic feature of numerous cardiovascular diseases and significantly impacts human health. However, effective treatment options for cardiac hypertrophy are still significantly unmet. Pedunculoside, a pentacyclic triterpenoid saponin from the traditional Chinese herb Ilex rotunda Thunb., exhibits various pharmacological properties such as anti-inflammatory and cardiovascular therapeutic effects, but its anti-hypertrophy efficacy and mechanisms have not yet been reported.

PURPOSE

This study aimed to confirm the ameliorating effect of pedunculoside on cardiac hypertrophy and elucidate its underlying mechanism.

METHODS

To investigate the effect of pedunculoside on cardiac hypertrophy, we used transverse aortic constriction (TAC) and isoproterenol hydrochloride (ISO) infusion to induce cardiac hypertrophy model in mice. Angiotensin II (Ang II) was used to mimic hypertrophy model in myocardial cells. Then, we utilized a biotin-tagged carabrone chemical probe and validation experiments to pinpoint pedunculoside's key targets. Further, molecular docking study and sites mutation were used to predict and identify the binding modes of pedunculoside to target. Finally, structural optimization was carried out to find new pedunculoside derivatives with stronger anti-hypertrophy activity and binding affinity to the target.

RESULTS

Our findings revealed for the first time that pedunculoside treatment significantly attenuated hypertrophic phenotypes in response to TAC and ISO. It also effectively reduced hypertrophy and fibrosis in myocardial cells exposed to Ang II stimulation. Mechanically, we identified transcription factor GATA-6 (GATA6) as a key target of pedunculoside for treating cardiac hypertrophy. Further studies demonstrated that pedunculoside blocks cardiac hypertrophy progression by inhibiting the transcriptional activation of GATA6 on promoting fetal gene expression. More importantly, a new pedunculoside derivative PE-3 with stronger anti-hypertrophy activity and affinity for GATA6 was discovered.

CONCLUSION

Our findings suggest that pedunculoside and PE-3 could be developed as promising drug candidates for cardiac hypertrophy treatment.

Systematic analysis identifies a connection between spatial and genomic variations of chromatin states

Chromatin states play important roles in the maintenance of cell identities, yet their spatial patterns remain poorly characterized at the organism scale. We developed a systematic approach to analyzing spatial epigenomic data and then applied it to a recently published spatial-CUT&Tag dataset that was obtained from a mouse embryo. We identified a set of spatial genes whose H3K4me3 patterns delineate tissue boundaries. These genes are enriched with tissue-specific transcription factors, and their corresponding genomic loci are marked by broad H3K4me3 domains. Integrative analysis with H3K27me3 profiles showed coordinated spatial transitions across tissue boundaries, which is marked by the continuous shortening of H3K4me3 domains and expansion of H3K27me3 domains. Motif-based analysis identified transcription factors whose activities change significantly during such transitions. Taken together, our systematic analyses reveal a strong connection between the genomic and spatial variations of chromatin states. A record of this paper's transparent peer review process is included in the supplemental information.

Discovery of a novel mutation F184S (c.551T>C) in GATA4 gene causing congenital heart disease in a consanguineous Saudi family

Background & aim

Congenital heart disease (CHD) is the most common cause of non-infectious deaths in infants worldwide. However, the molecular mechanisms underlying CHD remain unclear. Approximately 30 % of the causes are believed to be genetic mutations and chromosomal abnormalities. In this study, we aimed to identify the genetic causes of CHD in consanguineous families.

Methods

Fourth-generation pedigrees with CHD were recruited. The main cardiac features of the patient included absence of the right pulmonary artery and a large dilated left pulmonary artery. To determine the underlying genetic cause, whole-exome sequencing was performed and subsequently confirmed using Sanger sequencing and different online databases to study the pathogenesis of the identified gene mutation. An in-silico homology model was created using the Alphafold homology model structure of GATA4 (AF-P43694-F1). The missense3D online program was used to evaluate the structural alterations.

Results

We identified a deleterious mutation c.551T > C (p.Phe184Ser) in GATA4. GATA4 is a highly conserved zinc-finger transcription factor, and its continuous expression is essential for cardiogenesis during embryogenesis. The in-silico model suggested a compromised binding efficiency with other proteins. Several variant interpretation algorithms indicated that the F184S missense variant in GATA4 is damaging, whereas HOPE analysis indicated the functional impairment of DNA binding of transcription factors and zinc-ion binding activities of GATA4.

Conclusion

The variant identified in GATA4 appears to cause recessive CHD in the family. In silico analysis suggested that this variant was damaging and caused multiple structural and functional aberrations. This study may support prenatal screening of the fetus in this family to prevent diseases in new generations.

Gata6 functions in zebrafish endoderm to regulate late differentiating arterial pole cardiogenesis

Mutations in GATA6 are associated with congenital heart disease, most notably conotruncal structural defects. However, how GATA6 regulates cardiac morphology during embryogenesis is undefined. We used knockout and conditional mutant zebrafish alleles to investigate the spatiotemporal role of gata6 during cardiogenesis. Loss of gata6 specifically impacts atrioventricular valve formation and recruitment of epicardium, with a prominent loss of arterial pole cardiac cells, including those of the ventricle and outflow tract. However, there are no obvious defects in cardiac progenitor cell specification, proliferation or death. Conditional loss of gata6 starting at 24 h is sufficient to disrupt the addition of late differentiating cardiomyocytes at the arterial pole, with decreased expression levels of anterior secondary heart field (SHF) markers spry4 and mef2cb. Conditional loss of gata6 in the endoderm is sufficient to phenocopy the straight knockout, resulting in a significant loss of ventricular and outflow tract tissue. Exposure to a Dusp6 inhibitor largely rescues the loss of ventricular cells in gata6-/- larvae. Thus, gata6 functions in endoderm are mediated by FGF signaling to regulate the addition of anterior SHF progenitor derivatives during heart formation.

In Vitro Differentiation of Endometrium Stem Cells into Cardiomyocytes: The Putative Effect of miR-17-5p, miR-26b-5p, miR-32-5p, and SMAD6

Background

The important role of SMAD6 and several microRNAs (miRNAs), such as miR-17-5p, miR-26b-5p, and miR-32-5p, has been demonstrated in controlling the proliferation and differentiation of cardiomyocytes (CMs). Hence, this study was designed to assess the role of these regulatory factors in cardiac cell generation from human endometrium-derived mesenchymal stem cells (hEMSCs).

Methods

To induce transdifferentiation into CMs, hEMSCs were treated with a cardiac-inducing medium containing 5-azacytidine and bFGF for 30 days. Immunofluorescence staining and qRT-PCR, respectively, were used to measure the protein levels of SMAD6 and the mRNA expression of SMAD6 and the three miRNAs every six days.

Results

Our findings demonstrated the mesenchymal stem cell properties of hEMSCs and their ability to differentiate into various types of mesenchymal stem cells. The differentiated hEMSCs exhibited morphological features resembling CMs. During the induction period, the number of positive cells for SMAD6 protein and the expression level of miR-26b-5p increased and peaking on days 24 and 30, while the expression levels of miR-17-5p and miR-32-5p decreased. The Pearson correlation coefficients revealed that SMAD6 level is inversely correlated with miR-17-5p and miR-32-5p and directly correlated with miR-26b-5p.

Conclusions

Our results indicate that miR-17-5p, miR-26b-5p, miR-32-5p, and SMAD6 are potentially involved in the molecular signaling pathways of transdifferentiation of hEMSCs to CMs.

Cardiomyocyte maturation and its reversal during cardiac regeneration

Cardiovascular disease is a leading cause of death worldwide. Due to the limited proliferative and regenerative capacity of adult cardiomyocytes, the lost myocardium is not replenished efficiently and is replaced by a fibrotic scar, which eventually leads to heart failure. Current therapies to cure or delay the progression of heart failure are limited; hence, there is a pressing need for regenerative approaches to support the failing heart. Cardiomyocytes undergo a series of transcriptional, structural, and metabolic changes after birth (collectively termed maturation), which is critical for their contractile function but limits the regenerative capacity of the heart. In regenerative organisms, cardiomyocytes revert from their terminally differentiated state into a less mature state (ie, dedifferentiation) to allow for proliferation and regeneration to occur. Importantly, stimulating adult cardiomyocyte dedifferentiation has been shown to promote morphological and functional improvement after myocardial infarction, further highlighting the importance of cardiomyocyte dedifferentiation in heart regeneration. Here, we review several hallmarks of cardiomyocyte maturation, and summarize how their reversal facilitates cardiomyocyte proliferation and heart regeneration. A detailed understanding of how cardiomyocyte dedifferentiation is regulated will provide insights into therapeutic options to promote cardiomyocyte de-maturation and proliferation, and ultimately heart regeneration in mammals.

Broad H3K4me3 Domain Is Associated with Spatial Coherence during Mammalian Embryonic Development

It is well known that the chromatin states play a major role in cell-fate decision and cell-identity maintenance; however, the spatial variation of chromatin states in situ remains poorly characterized. Here, by leveraging recently available spatial-CUT&Tag data, we systematically characterized the global spatial organization of the H3K4me3 profiles in a mouse embryo. Our analysis identified a subset of genes with spatially coherent H3K4me3 patterns, which together delineate the tissue boundaries. The spatially coherent genes are strongly enriched with tissue-specific transcriptional regulators. Remarkably, their corresponding genomic loci are marked by broad H3K4me3 domains, which is distinct from the typical H3K4me3 signature. Spatial transition across tissue boundaries is associated with continuous shortening of the broad H3K4me3 domains as well as expansion of H3K27me3 domains. Our analysis reveals a strong connection between the genomic and spatial variation of chromatin states, which may play an important role in embryonic development.

The Tbx20-TLE interaction is essential for the maintenance of the second heart field

T-box transcription factor 20 (Tbx20) plays a multifaceted role in cardiac morphogenesis and controls a broad gene regulatory network. However, the mechanism by which Tbx20 activates and represses target genes in a tissue-specific and temporal manner remains unclear. Studies show that Tbx20 directly interacts with the Transducin-like Enhancer of Split (TLE) family of proteins to mediate transcriptional repression. However, a function for the Tbx20-TLE transcriptional repression complex during heart development has yet to be established. We created a mouse model with a two amino acid substitution in the Tbx20 EH1 domain, thereby disrupting the Tbx20-TLE interaction. Disruption of this interaction impaired crucial morphogenic events, including cardiac looping and chamber formation. Transcriptional profiling of Tbx20EH1Mut hearts and analysis of putative direct targets revealed misexpression of the retinoic acid pathway and cardiac progenitor genes. Further, we show that altered cardiac progenitor development and function contribute to the severe cardiac defects in our model. Our studies indicate that TLE-mediated repression is a primary mechanism by which Tbx20 controls gene expression.

Uncovering the Heterogeneity of Cardiac Lin-KIT+ Cells: A scRNA-seq Study on the Identification of Subpopulations

The reparative potential of cardiac Lin-KIT+ (KIT) cells is influenced by their population, but identifying their markers is challenging due to changes in phenotype during in vitro culture. Resolving this issue requires uncovering cell heterogeneity and discovering new subpopulations. Single-cell RNA sequencing (scRNA-seq) can identify KIT cell subpopulations, their markers, and signaling pathways. We used 10× genomic scRNA-seq to analyze cardiac-derived cells from adult mice and found 3 primary KIT cell populations: KIT1, characterized by high-KIT expression (KITHI), represents a population of cardiac endothelial cells; KIT2, which has low-KIT expression (KITLO), expresses transcription factors such as KLF4, MYC, and GATA6, as well as genes involved in the regulation of angiogenic cytokines; KIT3, with moderate KIT expression (KITMOD), expresses the cardiac transcription factor MEF2C and mesenchymal cell markers such as ENG. Cell-cell communication network analysis predicted the presence of the 3 KIT clusters as signal senders and receivers, including VEGF, CXCL, and BMP signaling. Metabolic analysis showed that KIT1 has the low activity of glycolysis and oxidative phosphorylation (OXPHOS), KIT2 has high glycolytic activity, and KIT3 has high OXPHOS and fatty acid degradation activity, indicating distinct metabolic adaptations of the 3 KIT populations. Through the systemic infusion of KIT1 cells in a mouse model of myocardial infarction, we observed their involvement in promoting the formation of new micro-vessels. In addition, in vitro spheroid culture experiments demonstrated the cardiac differentiation capacity of KIT2 cells.

Regulatory changes associated with the head to trunk developmental transition

BACKGROUND

Development of vertebrate embryos is characterized by early formation of the anterior tissues followed by the sequential extension of the axis at their posterior end to build the trunk and tail structures, first by the activity of the primitive streak and then of the tail bud. Embryological, molecular and genetic data indicate that head and trunk development are significantly different, suggesting that the transition into the trunk formation stage involves major changes in regulatory gene networks.

RESULTS

We explored those regulatory changes by generating differential interaction networks and chromatin accessibility profiles from the posterior epiblast region of mouse embryos at embryonic day (E)7.5 and E8.5. We observed changes in various cell processes, including several signaling pathways, ubiquitination machinery, ion dynamics and metabolic processes involving lipids that could contribute to the functional switch in the progenitor region of the embryo. We further explored the functional impact of changes observed in Wnt signaling associated processes, revealing a switch in the functional relevance of Wnt molecule palmitoleoylation, essential during gastrulation but becoming differentially required for the control of axial extension and progenitor differentiation processes during trunk formation. We also found substantial changes in chromatin accessibility at the two developmental stages, mostly mapping to intergenic regions and presenting differential footprinting profiles to several key transcription factors, indicating a significant switch in the regulatory elements controlling head or trunk development. Those chromatin changes are largely independent of retinoic acid, despite the key role of this factor in the transition to trunk development. We also tested the functional relevance of potential enhancers identified in the accessibility assays that reproduced the expression profiles of genes involved in the transition. Deletion of these regions by genome editing had limited effect on the expression of those genes, suggesting the existence of redundant enhancers that guarantee robust expression patterns.

CONCLUSIONS

This work provides a global view of the regulatory changes controlling the switch into the axial extension phase of vertebrate embryonic development. It also revealed mechanisms by which the cellular context influences the activity of regulatory factors, channeling them to implement one of several possible biological outputs.

Cooperative regulation of Zhx1 and hnRNPA1 drives the cardiac progenitor-specific transcriptional activation during cardiomyocyte differentiation

The zinc finger proteins (ZNFs) mediated transcriptional regulation is critical for cell fate transition. However, it is still unclear how the ZNFs realize their specific regulatory roles in the stage-specific determination of cardiomyocyte differentiation. Here, we reported that the zinc fingers and homeoboxes 1 (Zhx1) protein, transiently expressed during the cell fate transition from mesoderm to cardiac progenitors, was indispensable for the proper cardiomyocyte differentiation of mouse and human embryonic stem cells. Moreover, Zhx1 majorly promoted the specification of cardiac progenitors via interacting with hnRNPA1 and co-activated the transcription of a wide range of genes. In-depth mechanistic studies showed that Zhx1 was bound with hnRNPA1 by the amino acid residues (Thr111-His120) of the second Znf domain, thus participating in the formation of cardiac progenitors. Together, our study highlights the unrevealed interaction of Zhx1/hnRNPA1 for activating gene transcription during cardiac progenitor specification and also provides new evidence for the specificity of cell fate determination in cardiomyocyte differentiation.

Cohesin: an emerging master regulator at the heart of cardiac development

Cohesins are ATPase complexes that play central roles in cellular processes such as chromosome division, DNA repair, and gene expression. Cohesinopathies arise from mutations in cohesin proteins or cohesin complex regulators and encompass a family of related developmental disorders that present with a range of severe birth defects, affect many different physiological systems, and often lead to embryonic fatality. Treatments for cohesinopathies are limited, in large part due to the lack of understanding of cohesin biology. Thus, characterizing the signaling networks that lie upstream and downstream of cohesin-dependent pathways remains clinically relevant. Here, we highlight alterations in cohesins and cohesin regulators that result in cohesinopathies, with a focus on cardiac defects. In addition, we suggest a novel and more unifying view regarding the mechanisms through which cohesinopathy-based heart defects may arise.

Genetic Alterations of Transcription Factors and Signaling Molecules Involved in the Development of Congenital Heart Defects-A Narrative Review

Congenital heart defects (CHD) are the most common congenital abnormality, with an overall global birth prevalence of 9.41 per 1000 live births. The etiology of CHDs is complex and still poorly understood. Environmental factors account for about 10% of all cases, while the rest are likely explained by a genetic component that is still under intense research. Transcription factors and signaling molecules are promising candidates for studies regarding the genetic burden of CHDs. The present narrative review provides an overview of the current knowledge regarding some of the genetic mechanisms involved in the embryological development of the cardiovascular system. In addition, we reviewed the association between the genetic variation in transcription factors and signaling molecules involved in heart development, including TBX5, GATA4, NKX2-5 and CRELD1, and congenital heart defects, providing insight into the complex pathogenesis of this heterogeneous group of diseases. Further research is needed in order to uncover their downstream targets and the complex network of interactions with non-genetic risk factors for a better molecular-phenotype correlation.

miR-322 promotes the differentiation of embryonic stem cells into cardiomyocytes

Previous studies have shown that miR-322 regulates the functions of various stem cells. However, the role and mechanism of embryonic stem cell (ESCs) differentiation into cardiomyocytes remains unknown. Celf1 plays a vital role in stem cell differentiation and may be a potential target of miR-322 in ESCs' differentiation. We studied the function of miR-322An using mESCs transfected with lentivirus-mediated miR-322. RT-PCR results indicated that miR-322 increased NKX-2.5, MLC2V, and α-MHC mRNA expression, signifying that miR-322 might promote the differentiation of ESCs toward cardiomyocytes in vitro. The western blotting and immunofluorescence results confirmed this conclusion. In addition, the knockdown of miR-322 expression inhibited ESCs' differentiation toward cardiomyocytes in cultured ESCs in vitro. Western blotting results showed that miR-322 suppressed celf1 protein expression. Furthermore, Western blotting, RT-PCR, and immunofluorescence results showed that celf1 may inhibit ESCs' differentiation toward cardiomyocytes in vitro. Overall, the results indicate that miR-322 might promote ESCs' differentiation toward cardiomyocytes by regulating celf1 expression.

scChIX-seq infers dynamic relationships between histone modifications in single cells

Regulation of chromatin states involves the dynamic interplay between different histone modifications to control gene expression. Recent advances have enabled mapping of histone marks in single cells, but most methods are constrained to profile only one histone mark per cell. Here, we present an integrated experimental and computational framework, scChIX-seq (single-cell chromatin immunocleavage and unmixing sequencing), to map several histone marks in single cells. scChIX-seq multiplexes two histone marks together in single cells, then computationally deconvolves the signal using training data from respective histone mark profiles. This framework learns the cell-type-specific correlation structure between histone marks, and therefore does not require a priori assumptions of their genomic distributions. Using scChIX-seq, we demonstrate multimodal analysis of histone marks in single cells across a range of mark combinations. Modeling dynamics of in vitro macrophage differentiation enables integrated analysis of chromatin velocity. Overall, scChIX-seq unlocks systematic interrogation of the interplay between histone modifications in single cells.

TRIM35-mediated degradation of nuclear PKM2 destabilizes GATA4/6 and induces P53 in cardiomyocytes to promote heart failure

Pyruvate kinase M2 (PKM2) is a glycolytic enzyme that translocates to the nucleus to regulate transcription factors in different tissues or pathologic states. Although studied extensively in cancer, its biological role in the heart remains unresolved. PKM1 is more abundant than the PKM2 isoform in cardiomyocytes, and thus, we speculated that PKM2 is not genetically redundant to PKM1 and may be critical in regulating cardiomyocyte-specific transcription factors important for cardiac survival. Here, we showed that nuclear PKM2 ( S37 P-PKM2) in cardiomyocytes interacts with prosurvival and proapoptotic transcription factors, including GATA4, GATA6, and P53. Cardiomyocyte-specific PKM2-deficient mice ( Pkm2 Mut Cre + ) developed age-dependent dilated cardiac dysfunction and had decreased amounts of GATA4 and GATA6 (GATA4/6) but increased amounts of P53 compared to Control Cre +  hearts. Nuclear PKM2 prevented caspase-1–dependent cleavage and degradation of GATA4/6 while also providing a molecular platform for MDM2-mediated reduction of P53. In a preclinical heart failure mouse model, nuclear PKM2 and GATA4/6 were decreased, whereas P53 was increased in cardiomyocytes. Loss of nuclear PKM2 was ubiquitination dependent and associated with the induction of the E3 ubiquitin ligase TRIM35. In mice, cardiomyocyte-specific TRIM35 overexpression resulted in decreased S37 P-PKM2 and GATA4/6 along with increased P53 in cardiomyocytes compared to littermate controls and similar cardiac dysfunction to Pkm2 Mut Cre +  mice. In patients with dilated left ventricles, increase in TRIM35 was associated with decreased S37 P-PKM2 and GATA4/6 and increased P53. This study supports a previously unrecognized role for PKM2 as a molecular platform that mediates cell signaling events essential for cardiac survival.

The centrosomal protein 83 (CEP83) regulates human pluripotent stem cell differentiation toward the kidney lineage

During embryonic development, the mesoderm undergoes patterning into diverse lineages including axial, paraxial, and lateral plate mesoderm (LPM). Within the LPM, the so-called intermediate mesoderm (IM) forms kidney and urogenital tract progenitor cells, while the remaining LPM forms cardiovascular, hematopoietic, mesothelial, and additional progenitor cells. The signals that regulate these early lineage decisions are incompletely understood. Here, we found that the centrosomal protein 83 (CEP83), a centriolar component necessary for primary cilia formation and mutated in pediatric kidney disease, influences the differentiation of human-induced pluripotent stem cells (hiPSCs) toward IM. We induced inactivating deletions of CEP83 in hiPSCs and applied a 7-day in vitro protocol of IM kidney progenitor differentiation, based on timed application of WNT and FGF agonists. We characterized induced mesodermal cell populations using single-cell and bulk transcriptomics and tested their ability to form kidney structures in subsequent organoid culture. While hiPSCs with homozygous CEP83 inactivation were normal regarding morphology and transcriptome, their induced differentiation into IM progenitor cells was perturbed. Mesodermal cells induced after 7 days of monolayer culture of CEP83-deficient hiPCS exhibited absent or elongated primary cilia, displayed decreased expression of critical IM genes (PAX8, EYA1, HOXB7), and an aberrant induction of LPM markers (e.g. FOXF1, FOXF2, FENDRR, HAND1, HAND2). Upon subsequent organoid culture, wildtype cells differentiated to form kidney tubules and glomerular-like structures, whereas CEP83-deficient cells failed to generate kidney cell types, instead upregulating cardiomyocyte, vascular, and more general LPM progenitor markers. Our data suggest that CEP83 regulates the balance of IM and LPM formation from human pluripotent stem cells, identifying a potential link between centriolar or ciliary function and mesodermal lineage induction.

GATA6 is a crucial factor for Myocd expression in the visceral smooth muscle cell differentiation program of the murine ureter

Smooth muscle cells (SMCs) are a crucial component of the mesenchymal wall of the ureter, as they account for the efficient removal of the urine from the renal pelvis to the bladder by means of their contractile activity. Here, we show that the zinc-finger transcription factor gene Gata6 is expressed in mesenchymal precursors of ureteric SMCs under the control of BMP4 signaling. Mice with a conditional loss of Gata6 in these precursors exhibit a delayed onset and reduced level of SMC differentiation and peristaltic activity, as well as dilatation of the ureter and renal pelvis (hydroureternephrosis) at birth and at postnatal stages. Molecular profiling revealed a delayed and reduced expression of the myogenic driver gene Myocd, but the activation of signaling pathways and transcription factors previously implicated in activation of the visceral SMC program in the ureter was unchanged. Additional gain-of-function experiments suggest that GATA6 cooperates with FOXF1 in Myocd activation and SMC differentiation, possibly as pioneer and lineage-determining factors, respectively.

Modeling congenital heart disease: lessons from mice, hPSC-based models, and organoids

Congenital heart defects (CHDs) are among the most common birth defects, but their etiology has long been mysterious. In recent decades, the development of a variety of experimental models has led to a greater understanding of the molecular basis of CHDs. In this review, we contrast mouse models of CHD, which maintain the anatomical arrangement of the heart, and human cellular models of CHD, which are more likely to capture human-specific biology but lack anatomical structure. We also discuss the recent development of cardiac organoids, which are a promising step toward more anatomically informative human models of CHD.

Towards Understanding the Gene-Specific Roles of GATA Factors in Heart Development: Does GATA4 Lead the Way?

Transcription factors play crucial roles in the regulation of heart induction, formation, growth and morphogenesis. Zinc finger GATA transcription factors are among the critical regulators of these processes. GATA4, 5 and 6 genes are expressed in a partially overlapping manner in developing hearts, and GATA4 and 6 continue their expression in adult cardiac myocytes. Using different experimental models, GATA4, 5 and 6 were shown to work together not only to ensure specification of cardiac cells but also during subsequent heart development. The complex involvement of these related gene family members in those processes is demonstrated through the redundancy among them and crossregulation of each other. Our recent identification at the genome-wide level of genes specifically regulated by each of the three family members and our earlier discovery that gata4 and gata6 function upstream, while gata5 functions downstream of noncanonical Wnt signalling during cardiac differentiation, clearly demonstrate the functional differences among the cardiogenic GATA factors. Such suspected functional differences are worth exploring more widely. It appears that in the past few years, significant advances have indeed been made in providing a deeper understanding of the mechanisms by which each of these molecules function during heart development. In this review, I will therefore discuss current evidence of the role of individual cardiogenic GATA factors in the process of heart development and emphasize the emerging central role of GATA4.

Gene expression and transcriptional regulation driven by transcription factors involved in congenital heart defects

BACKGROUND

Congenital heart disease (CHD) is one of the most important birth defects caused by more than one mutated gene. Mutations in the genes could cause different types of congenital heart defects including atrial septal defect (ASD), tetralogy of Fallot (TOF), and ventricular septal defect (VSD).

OBJECTIVES

Cardiac transcription factors are key players for heart development and are actively involved in controlling stress regulation of the heart. Transcription factors are sequence-specific DNA binding proteins that control the process of transcription and work in a synergistic manner. We aim to characterize core cardiac transcription factors including NKX2-5, TBX, SRF, GATA4, and MEF2, which encode homeobox and MADS domain and play a crucial role in heart development.

METHODS

In this study, we have explored the important transcription factors involved in cardiac development and genes controlling the expression and regulation process by using the bioinformatics approach.

RESULTS

We have predicted the orthologs and homologs based on their evolutionary history, conserved protein domains, functional sites, and 3D structures for better understanding and presentation of factors responsible for causing CHD. Results showed the importance of these transcription factors for normal heart functioning and development.

CONCLUSION

Understanding the molecular pathways and genetic basis of CHD will help to open a new door for the treatment of patients with cardiac defects.

GATA4/5/6 family transcription factors are conserved determinants of cardiac versus pharyngeal mesoderm fate

GATA4/5/6 transcription factors play essential, conserved roles in heart development. To understand how GATA4/5/6 modulates the mesoderm-to-cardiac fate transition, we labeled, isolated, and performed single-cell gene expression analysis on cells that express gata5 at precardiac time points spanning zebrafish gastrulation to somitogenesis. We found that most mesendoderm-derived lineages had dynamic gata5/6 expression. In the absence of Gata5/6, the population structure of mesendoderm-derived cells was substantially altered. In addition to the expected absence of cardiac mesoderm, we confirmed a concomitant expansion of cranial-pharyngeal mesoderm. Moreover, Gata5/6 loss led to extensive changes in chromatin accessibility near cardiac and pharyngeal genes. Functional analyses in zebrafish and the tunicate Ciona, which has a single GATA4/5/6 homolog, revealed that GATA4/5/6 acts upstream of tbx1 to exert essential and cell-autonomous roles in promoting cardiac and inhibiting pharyngeal mesoderm identity. Overall, cardiac and pharyngeal mesoderm fate choices are achieved through an evolutionarily conserved GATA4/5/6 regulatory network.

Two Isoforms of serpent Containing Either One or Two GATA Zinc Fingers Provide Functional Diversity During Drosophila Development

GATA transcription factors play crucial roles in various developmental processes in organisms ranging from flies to humans. In mammals, GATA factors are characterized by the presence of two highly conserved domains, the N-terminal (N-ZnF) and the C-terminal (C-ZnF) zinc fingers. The Drosophila GATA factor Serpent (Srp) is produced in different isoforms that contains either both N-ZnF and C-ZnF (SrpNC) or only the C-ZnF (SrpC). Here, we investigated the functional roles ensured by each of these isoforms during Drosophila development. Using the CRISPR/Cas9 technique, we generated new mutant fly lines deleted for one (ΔsrpNC) or the other (ΔsrpC) encoded isoform, and a third one with a single point mutation in the N-ZnF that alters its interaction with its cofactor, the Drosophila FOG homolog U-shaped (Ush). Analysis of these mutants revealed that the Srp zinc fingers are differentially required for Srp to fulfill its functions. While SrpC is essential for embryo to adult viability, SrpNC, which is the closest conserved isoform to that of vertebrates, is not. However, to ensure its specific functions in larval hematopoiesis and fertility, Srp requires the presence of both N- and C-ZnF (SrpNC) and interaction with its cofactor Ush. Our results also reveal that in vivo the presence of N-ZnF restricts rather than extends the ability of GATA factors to regulate the repertoire of C-ZnF bound target genes.

Dissecting the Complexity of Early Heart Progenitor Cells

Early heart development depends on the coordinated participation of heterogeneous cell sources. As pioneer work from Adriana C. Gittenberger-de Groot demonstrated, characterizing these distinct cell sources helps us to understand congenital heart defects. Despite decades of research on the segregation of lineages that form the primitive heart tube, we are far from understanding its full complexity. Currently, single-cell approaches are providing an unprecedented level of detail on cellular heterogeneity, offering new opportunities to decipher its functional role. In this review, we will focus on three key aspects of early heart morphogenesis: First, the segregation of myocardial and endocardial lineages, which yields an early lineage diversification in cardiac development; second, the signaling cues driving differentiation in these progenitor cells; and third, the transcriptional heterogeneity of cardiomyocyte progenitors of the primitive heart tube. Finally, we discuss how single-cell transcriptomics and epigenomics, together with live imaging and functional analyses, will likely transform the way we delve into the complexity of cardiac development and its links with congenital defects.

Cardiac specification during gastrulation - The Yellow Brick Road leading to Tinman

The question of how the heart develops, and the genetic networks governing this process have become intense areas of research over the past several decades. This research is propelled by classical developmental studies and potential clinical applications to understand and treat congenital conditions in which cardiac development is disrupted. Discovery of the tinman gene in Drosophila, and examination of its vertebrate homolog Nkx2.5, along with other core cardiac transcription factors has revealed how cardiac progenitor differentiation and maturation drives heart development. Careful observation of cardiac morphogenesis along with lineage tracing approaches indicated that cardiac progenitors can be divided into two broad classes of cells, namely the first and second heart fields, that contribute to the heart in two distinct waves of differentiation. Ample evidence suggests that the fate of individual cardiac progenitors is restricted to distinct cardiac structures quite early in development, well before the expression of canonical cardiac progenitor markers like Nkx2.5. Here we review the initial specification of cardiac progenitors, discuss evidence for the early patterning of cardiac progenitors during gastrulation, and consider how early gene expression programs and epigenetic patterns can direct their development. A complete understanding of when and how the developmental potential of cardiac progenitors is determined, and their potential plasticity, is of great interest developmentally and also has important implications for both the study of congenital heart disease and therapeutic approaches based on cardiac stem cell programming.

Ventricular, atrial, and outflow tract heart progenitors arise from spatially and molecularly distinct regions of the primitive streak

The heart develops from 2 sources of mesoderm progenitors, the first and second heart field (FHF and SHF). Using a single-cell transcriptomic assay combined with genetic lineage tracing and live imaging, we find the FHF and SHF are subdivided into distinct pools of progenitors in gastrulating mouse embryos at earlier stages than previously thought. Each subpopulation has a distinct origin in the primitive streak. The first progenitors to leave the primitive streak contribute to the left ventricle, shortly after right ventricle progenitor emigrate, followed by the outflow tract and atrial progenitors. Moreover, a subset of atrial progenitors are gradually incorporated in posterior locations of the FHF. Although cells allocated to the outflow tract and atrium leave the primitive streak at a similar stage, they arise from different regions. Outflow tract cells originate from distal locations in the primitive streak while atrial progenitors are positioned more proximally. Moreover, single-cell RNA sequencing demonstrates that the primitive streak cells contributing to the ventricles have a distinct molecular signature from those forming the outflow tract and atrium. We conclude that cardiac progenitors are prepatterned within the primitive streak and this prefigures their allocation to distinct anatomical structures of the heart. Together, our data provide a new molecular and spatial map of mammalian cardiac progenitors that will support future studies of heart development, function, and disease.

Fibroblast GATA-4 and GATA-6 promote myocardial adaptation to pressure overload by enhancing cardiac angiogenesis

Heart failure due to high blood pressure or ischemic injury remains a major problem for millions of patients worldwide. Despite enormous advances in deciphering the molecular mechanisms underlying heart failure progression, the cell-type specific adaptations and especially intercellular signaling remain poorly understood. Cardiac fibroblasts express high levels of cardiogenic transcription factors such as GATA-4 and GATA-6, but their role in fibroblasts during stress is not known. Here, we show that fibroblast GATA-4 and GATA-6 promote adaptive remodeling in pressure overload induced cardiac hypertrophy. Using a mouse model with specific single or double deletion of Gata4 and Gata6 in stress activated fibroblasts, we found a reduced myocardial capillarization in mice with Gata4/6 double deletion following pressure overload, while single deletion of Gata4 or Gata6 had no effect. Importantly, we confirmed the reduced angiogenic response using an in vitro co-culture system with Gata4/6 deleted cardiac fibroblasts and endothelial cells. A comprehensive RNA-sequencing analysis revealed an upregulation of anti-angiogenic genes upon Gata4/6 deletion in fibroblasts, and siRNA mediated downregulation of these genes restored endothelial cell growth. In conclusion, we identified a novel role for the cardiogenic transcription factors GATA-4 and GATA-6 in heart fibroblasts, where both proteins act in concert to promote myocardial capillarization and heart function by directing intercellular crosstalk.

Generation of cell-permeant recombinant human transcription factor GATA4 from E. coli

Transcription factor GATA4 is expressed during early embryogenesis and is vital for proper development. In addition, it is a crucial reprogramming factor for deriving functional cardiomyocytes and was recently identified as a tumor suppressor protein in various cancers. To generate a safe and effective molecular tool that can potentially be used in a cell reprogramming process and as an anti-cancer agent, we have identified optimal expression parameters to obtain soluble expression of human GATA4 in E. coli and purified the same to homogeneity under native conditions using immobilized metal ion affinity chromatography. The identity of GATA4 protein was confirmed using western blotting and mass spectrometry. Using circular dichroism spectroscopy, it was demonstrated that the purified recombinant protein has maintained its secondary structure, primarily comprising of random coils and α-helices. Subsequently, this purified recombinant protein was applied to human cells and was found that it was non-toxic and able to enter the cells as well as translocate to the nucleus. Prospectively, this cell- and nuclear-permeant molecular tool is suitable for cell reprogramming experiments and can be a safe and effective therapeutic agent for cancer therapy.

Cardiac Development: A Glimpse on Its Translational Contributions

Cardiac development is a complex developmental process that is initiated soon after gastrulation, as two sets of precardiac mesodermal precursors are symmetrically located and subsequently fused at the embryonic midline forming the cardiac straight tube. Thereafter, the cardiac straight tube invariably bends to the right, configuring the first sign of morphological left–right asymmetry and soon thereafter the atrial and ventricular chambers are formed, expanded and progressively septated. As a consequence of all these morphogenetic processes, the fetal heart acquired a four-chambered structure having distinct inlet and outlet connections and a specialized conduction system capable of directing the electrical impulse within the fully formed heart. Over the last decades, our understanding of the morphogenetic, cellular, and molecular pathways involved in cardiac development has exponentially grown. Multiples aspects of the initial discoveries during heart formation has served as guiding tools to understand the etiology of cardiac congenital anomalies and adult cardiac pathology, as well as to enlighten novels approaches to heal the damaged heart. In this review we provide an overview of the complex cellular and molecular pathways driving heart morphogenesis and how those discoveries have provided new roads into the genetic, clinical and therapeutic management of the diseased hearts.

MiR-33a-5p targets NOMO1 to modulate human cardiomyocyte progenitor cells proliferation and differentiation and apoptosis

PURPOSE

MicroRNA (miRNA) is known to be involved in the pathological process of congenital heart disease (CHD), and nodal modulator1 (NOMO1) is a critical determinant of heart formation. The present study aims to discover the effect of miR-33a-5p and NOMO1 on CHD.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect expressions of miR-33a-5p mimic or inhibitor and overexpressed NOMO1 plasmid orNOMO1 knockdown. Human cardiomyocyte progenitor cells (hCMPCs) proliferation was measured by cell counting kit-8 (CCK-8) at 24, 48 and 72 h. Flow cytometry was applied to investigate hCMPCs cell cycle progression and apoptosis. Expressions of cell apoptotic proteins Bax, Cleaved(C) caspase-3 and Bcl-2, and expressions of cardiomyocyte differentiation markers GATA4, troponin T (cTnT) and myocyte enhancer factor2C (MEF2C) in hCMPCs were identified by qRT-PCR and western blot. Target genes and potential binding sites of NOMO1 and miR-33a-5p were predicted with Targetscan 7.2, and was confirmed through dual-luciferase reporter assay.

RESULTS

Up-regulation of miR-33a-5p inhibited hCMPCs proliferation, cell cycle G0/S transition but promoted hCMPCs apoptosis, which was partially mitigated by overexpressed NOMO1. NOMO1 was the target gene of miR-33a-5p. Expressions of Bax and C caspase-3 were enhanced but expressions of Bcl-2, GATA4, cTnT and MEF2C were reduced by up-regulation of miR-33a-5p, which was partially mitigated by overexpressed NOMO1.

CONCLUSION

Up-regulation of miR-33a-5p inhibited hCMPCs proliferation, cell cycle G0/S transition and differentiation into cardiomyocytes but promoted apoptosis via targeting NOMO1.

A long non-coding RNA GATA6-AS1 adjacent to GATA6 is required for cardiomyocyte differentiation from human pluripotent stem cells

Long noncoding RNAs (lncRNAs) are crucial in many cellular processes, yet relatively few have been shown to regulate human cardiomyocyte differentiation. Here, we demonstrate an essential role of GATA6 antisense RNA 1 (GATA6-AS1) in cardiomyocyte differentiation from human pluripotent stem cells (hPSCs). GATA6-AS1 is adjacent to cardiac transcription factor GATA6. We found that GATA6-AS1 was nuclear-localized and transiently upregulated along with GATA6 during the early stage of cardiomyocyte differentiation. The knockdown of GATA6-AS1 did not affect undifferentiated cell pluripotency but inhibited cardiomyocyte differentiation, as indicated by no or few beating cardiomyocytes and reduced expression of cardiomyocyte-specific proteins. Upon cardiac induction, the knockdown of GATA6-AS1 decreased GATA6 expression, altered Wnt-signaling gene expression, and reduced mesoderm development. Further characterization of the intergenic region between genomic regions of GATA6-AS1 and GATA6 indicated that the expression of GATA6-AS1 and GATA6 were regulated by a bidirectional promoter within the intergenic region. Consistently, GATA6-AS1 and GATA6 were co-expressed in several human tissues including the heart, similar to the mirror expression pattern of GATA6-AS1 and GATA6 during cardiomyocyte differentiation. Overall, these findings reveal a previously unrecognized and functional role of lncRNA GATA6-AS1 in controlling human cardiomyocyte differentiation.

Specificity, redundancy and dosage thresholds among gata4/5/6 genes during zebrafish cardiogenesis

The Gata4/5/6 sub-family of zinc finger transcription factors regulate many aspects of cardiogenesis. However, critical roles in extra-embryonic endoderm also challenge comprehensive analysis during early mouse cardiogenesis, while zebrafish models have previously relied on knockdown assays. We generated targeted deletions to disrupt each gata4/5/6 gene in zebrafish and analyzed cardiac phenotypes in single, double and triple mutants. The analysis confirmed that loss of gata5 causes cardia bifida and validated functional redundancies for gata5/6 in cardiac precursor specification. Surprisingly, we discovered that gata4 is dispensable for early zebrafish development, while loss of one gata4 allele can suppress the bifid phenotype of the gata5 mutant. The gata4 mutants eventually develop an age-dependent cardiomyopathy. By combining combinations of mutant alleles, we show that cardiac specification depends primarily on an overall dosage of gata4/5/6 alleles rather than a specific gene. We also identify a specific role for gata6 in controlling ventricle morphogenesis through regulation of both the first and second heart field, while loss of both gata4/6 eliminates the ventricle. Thus, different developmental programs are dependent on total dosage, certain pairs, or specific gata4/5/6 genes during embryonic cardiogenesis.

This article has an associated First Person interview with the first author of the paper.

Summary: Targeted mutations were generated for each of the three gata4/5/6 genes in zebrafish to define functions for individual or combinations of these related transcription factors during cardiogenesis.

Electrical stimulation induces differentiation of human cardiosphere-derived cells (hCDCs) to committed cardiomyocyte

Logistic complexities of heart transplantation embossed the necessity of utilizing novel methods, which enable heart regeneration. Human cardiosphere-derived cells (hCDCs) are taken into consideration as a promising cell resource in cell therapy in recent years. In this study, we designed an electrochemical stimulation system, which sends square pulses to the hCDCs and records their electrical response. Morphology, viability and differentiation of hCDCs are monitored at certain time courses of the treatment. Differentiating hCDCs aligned perpendicularly with respect to the direction of applied electric current, and obtained a spindle-like morphology, while they remained viable. At the same time, specific cardiac marker genes including GATA4, cTnT and α-MHC showed a considerable up-regulation. Our findings confirm that hCDCs differentiate to committed cardiomyocytes when hCDCs receive an electrical energy of 0.06 - 0.12 Wh. This amount of electrical energy could be applied to the stem cells using versatile electrical stimulation patterns via commercially available devices.

HYDIN loss-of-function inhibits GATA4 expression and enhances atrial septal defect risk

BACKGROUND

Mutations affecting cardiac structural genes can lead to congenital heart diseases (CHDs). Axonemal Central Pair Apparatus Protein (HYDIN) is a ciliary protein previously linked to congenital cardiomyopathy. However, the role of HYDIN in the aetiology of CHDs is thus far unknown. Herein, we explore the function of HYDIN in heart development and CHDs.

METHODS

The function of HYDIN in cardiac differentiation was assessed in vitro using HYDIN siRNAs, HYDIN overexpression, and HYDIN short hairpin RNA (shRNA)-GATA binding protein 4 (GATA4) cDNA rescue constructs in the human embryonic stem cell (hESC) line HES3. To assess Hydin's function in vivo, we generated shRNA-mediated Hydin knockdown transgenic mice. We characterized the functional mechanisms of the most common human HYDIN variant associated with atrial septal defect (ASD) risk (71098693 mutant, c.A2207C) in cardiac-differentiating HES3 cells.

RESULTS

HYDIN functions as a positive regulator of human cardiomyocyte differentiation and promotes expression of cardiac contractile genes in hESC cells. This is mediated through GATA4, a critical transcription factor in heart development. Cardiac-specific Hydin knockdown in vivo leads to Gata4 downregulation and enhanced atrial septal defect (ASD) risk in mice. The c.A2207C HYDIN mutation reduces GATA4 expression in hESC cells.

CONCLUSION

HYDIN loss-of-function inhibits GATA4 expression and enhances ASD risk. We also establish the regulation of a key transcription factor in heart development by a ciliary protein.

Modeling early stages of endoderm development in epiblast stem cell aggregates with supply of extracellular matrices

Endoderm precursors expressing FoxA2 and Sox17 develop from the epiblast through the gastrulation process. In this study, we developed an experimental system to model the endoderm-generating gastrulation process using epiblast stem cells (EpiSCs). To this end, we established an EpiSC line i22, in which enhanced green fluorescent protein is coexpressed with Foxa2. Culturing i22 EpiSCs as aggregates for a few days was sufficient to initiate Foxa2 expression, and further culturing of the aggregates in Matrigel promoted the sequential activation of transcription factor genes involved in endoderm precursor development, e.g., Eomes, Gsc, and Sox17. In aggregation culture of i22 cells for 3 days, all cells expressed POU5F1, SOX2, and E-cadherin, a signature of the epiblast, whereas expression of GATA4 and SOX17 was also activated moderately in dispersed cells, suggesting priming of these cells to endodermal development. Embedding the aggregates in Matrigel for further 3 days elicited migration of the cells into the lumen of laminin-rich matrices covering the aggregates, in which FOXA2 and SOX17 were expressed at a high level with the concomitant loss of E-cadherin, indicating the migratory phase of endodermal precursors. Prolonged culturing of the aggregates generated three segregating cell populations found in post-gastrulation stage embryos: (1) definitive endoderm co-expressing high SOX17, GATA4, and E-cadherin, (2) mesodermal cells expressing a low level of GATA4 and lacking E-cadherin, and (3) primed epiblast cells expressing POU5F1, SOX2 without E-cadherin. Thus, aggregation of EpiSCs followed by embedding of aggregates in the laminin-rich matrix models the gastrulation-dependent endoderm precursor development.

PinX1t, a Novel PinX1 Transcript Variant, Positively Regulates Cardiogenesis of Embryonic Stem Cells

Background

Pin2/TRF1‐interacting protein, PinX1, was previously identified as a tumor suppressor. Here, we discovered a novel transcript variant of mPinX1 (mouse PinX1), mPinX1t (mouse PinX1t), in embryonic stem cells (ESCs). The aims of this investigation were (1) to detect the presence of mPinX1 and mPinX1t in ESCs and their differentiation derivatives; (2) to investigate the role of mPinX1 and mPinX1t on regulating the characteristics of undifferentiated ESCs and the cardiac differentiation of ESCs; (3) to elucidate the molecular mechanisms of how mPinX1 and mPinX1t regulate the cardiac differentiation of ESCs.

Methods and Results

By 5′ rapid amplification of cDNA ends, 3′ rapid amplification of cDNA ends, and polysome fractionation followed by reverse transcription–polymerase chain reaction, mPinX1t transcript was confirmed to be an intact mRNA that is actively translated. Western blot confirmed the existence of mPinX1t protein. Overexpression or knockdown of mPinX1 (both decreased mPinX1t expression) both decreased while overexpression of mPinX1t increased the cardiac differentiation of ESCs. Although both mPinX1 and mPinX1t proteins were found to bind to cardiac transcription factor mRNAs, only mPinX1t protein but not mPinX1 protein was found to bind to nucleoporin 133 protein, a nuclear pore complex component. In addition, mPinX1t‐containing cells were found to have a higher cytosol‐to‐nucleus ratio of cardiac transcription factor mRNAs when compared with that in the control cells. Our data suggested that mPinX1t may positively regulate cardiac differentiation by enhancing export of cardiac transcription factor mRNAs through interacting with nucleoporin 133.

Conclusions

We discovered a novel transcript variant of mPinX1, the mPinX1t, which positively regulates the cardiac differentiation of ESCs.

A distal enhancer maintaining Hoxa1 expression orchestrates retinoic acid-induced early ESCs differentiation

Retinoic acid (RA) induces rapid differentiation of embryonic stem cells (ESCs), partly by activating expression of the transcription factor Hoxa1, which regulates downstream target genes that promote ESCs differentiation. However, mechanisms of RA-induced Hoxa1 expression and ESCs early differentiation remain largely unknown. Here, we identify a distal enhancer interacting with the Hoxa1 locus through a long-range chromatin loop. Enhancer deletion significantly inhibited expression of RA-induced Hoxa1 and endoderm master control genes such as Gata4 and Gata6. Transcriptome analysis revealed that RA-induced early ESCs differentiation was blocked in Hoxa1 enhancer knockout cells, suggesting a requirement for the enhancer. Restoration of Hoxa1 expression partly rescued expression levels of ∼40% of genes whose expression changed following enhancer deletion, and ∼18% of promoters of those rescued genes were directly bound by Hoxa1. Our data show that a distal enhancer maintains Hoxa1 expression through long-range chromatin loop and that Hoxa1 directly regulates downstream target genes expression and then orchestrates RA-induced early differentiation of ESCs. This discovery reveals mechanisms of a novel enhancer regulating RA-induced Hoxa genes expression and early ESCs differentiation.

Genetics of Congenital Heart Disease

Congenital heart disease (CHD) is one of the most common birth defects. Studies in animal models and humans have indicated a genetic etiology for CHD. About 400 genes have been implicated in CHD, encompassing transcription factors, cell signaling molecules, and structural proteins that are important for heart development. Recent studies have shown genes encoding chromatin modifiers, cilia related proteins, and cilia-transduced cell signaling pathways play important roles in CHD pathogenesis. Elucidating the genetic etiology of CHD will help improve diagnosis and the development of new therapies to improve patient outcomes.

Combinatorial chromatin dynamics foster accurate cardiopharyngeal fate choices

During embryogenesis, chromatin accessibility profiles control lineage-specific gene expression by modulating transcription, thus impacting multipotent progenitor states and subsequent fate choices. Subsets of cardiac and pharyngeal/head muscles share a common origin in the cardiopharyngeal mesoderm, but the chromatin landscapes that govern multipotent progenitors competence and early fate choices remain largely elusive. Here, we leveraged the simplicity of the chordate model Ciona to profile chromatin accessibility through stereotyped transitions from naive Mesp+ mesoderm to distinct fate-restricted heart and pharyngeal muscle precursors. An FGF-Foxf pathway acts in multipotent progenitors to establish cardiopharyngeal-specific patterns of accessibility, which govern later heart vs. pharyngeal muscle-specific expression profiles, demonstrating extensive spatiotemporal decoupling between early cardiopharyngeal enhancer accessibility and late cell-type-specific activity. We found that multiple cis-regulatory elements, with distinct chromatin accessibility profiles and motif compositions, are required to activate Ebf and Tbx1/10, two key determinants of cardiopharyngeal fate choices. We propose that these 'combined enhancers' foster spatially and temporally accurate fate choices, by increasing the repertoire of regulatory inputs that control gene expression, through either accessibility and/or activity.

GATA factor transcriptional activity: Insights from genome-wide binding profiles

The members of the GATA family of transcription factors have homologous zinc fingers and bind to similar sequence motifs. Recent advances in genome-wide technologies and the integration of bioinformatics data have led to a better understanding of how GATA factors regulate gene expression; GATA-factor-induced transcriptional and epigenetic changes have now been analyzed at unprecedented levels of detail. Here, we review the results of genome-wide studies of GATA factor occupancy in human and murine cell lines and primary cells (as determined by chromatin immunoprecipitation sequencing), and then discuss the molecular mechanisms underlying the mediation of transcriptional and epigenetic regulation by GATA factors.

Key Regulators of Cardiovascular Differentiation and Regeneration: Harnessing the Potential of Direct Reprogramming to Treat Heart Failure

Cardiovascular diseases remain a leading cause of death worldwide, with the number of patients with heart failure increasing rapidly in aging societies. As adult cardiomyocytes are terminally differentiated cells and opportunities for heart transplantation are very limited, regenerative medicine may become a game changer in heart failure treatment. To develop strategies for generating cardiomyocytes, vascular cells, and other supporting cells, it is necessary to understand the mechanism of cardiovascular differentiation during development and from pluripotent stem cells. Master regulators for cardiovascular differentiation can generate new cardiomyocytes and vascular cells directly from other differentiated cells such as fibroblasts. Fibroblasts can be directly reprogrammed into cardiomyocytes by overexpressing a combination of 3 cardiac-specific transcription factors (Gata4, Mef2c, Tbx5) both in vitro and in vivo, which restores cardiac function after myocardial infarction in mice. Moreover, a direct reprogramming-based approach can be used to identify new key regulators of the cardiovascular mesoderm, which can differentiate into all 3 types of cardiovascular cells including cardiomyocytes, endothelial cells, and smooth muscle cells. This review provides a perspective on how key regulators for cardiovascular differentiation and regeneration can be identified and used to develop new treatments for heart failure.

Gata4-Dependent Differentiation of c-Kit+-Derived Endothelial Cells Underlies Artefactual Cardiomyocyte Regeneration in the Heart

Supplemental Digital Content is available in the text.

Background:

Although c-Kit⁺ adult progenitor cells were initially reported to produce new cardiomyocytes in the heart, recent genetic evidence suggests that such events are exceedingly rare. However, to determine if these rare events represent true de novo cardiomyocyte formation, we deleted the necessary cardiogenic transcription factors Gata4 and Gata6 from c-Kit–expressing cardiac progenitor cells.

Methods:

Kit allele–dependent lineage tracing and fusion analysis were performed in mice following simultaneous Gata4 and Gata6 cell type–specific deletion to examine rates of putative de novo cardiomyocyte formation from c-Kit⁺ cells. Bone marrow transplantation experiments were used to define the contribution of Kit allele–derived hematopoietic cells versus Kit lineage–dependent cells endogenous to the heart in contributing to apparent de novo lineage-traced cardiomyocytes. A Tie2^CreERT2 transgene was also used to examine the global impact of Gata4 deletion on the mature cardiac endothelial cell network, which was further evaluated with select angiogenesis assays.

Results:

Deletion of Gata4 in Kit lineage–derived endothelial cells or in total endothelial cells using the Tie2^CreERT2 transgene, but not from bone morrow cells, resulted in profound endothelial cell expansion, defective endothelial cell differentiation, leukocyte infiltration into the heart, and a dramatic increase in Kit allele–dependent lineage-traced cardiomyocytes. However, this increase in labeled cardiomyocytes was an artefact of greater leukocyte-cardiomyocyte cellular fusion because of defective endothelial cell differentiation in the absence of Gata4.

Conclusions:

Past identification of presumed de novo cardiomyocyte formation in the heart from c-Kit⁺ cells using Kit allele lineage tracing appears to be an artefact of labeled leukocyte fusion with cardiomyocytes. Deletion of Gata4 from c-Kit⁺ endothelial progenitor cells or adult endothelial cells negatively impacted angiogenesis and capillary network integrity.

Developmental origins for semilunar valve stenosis identified in mice harboring congenital heart disease-associated GATA4 mutation

Congenital heart defects affect ∼2% of live births and often involve malformations of the semilunar (aortic and pulmonic) valves. We previously reported a highly penetrant GATA4 p.Gly296Ser mutation in familial, congenital atrial septal defects and pulmonic valve stenosis and showed that mice harboring the orthologous G295S disease-causing mutation display not only atrial septal defects, but also semilunar valve stenosis. Here, we aimed to characterize the role of Gata4 in semilunar valve development and stenosis using the Gata4^G295Ski/wt mouse model. GATA4 is highly expressed in developing valve endothelial and interstitial cells. Echocardiographic examination of Gata4^G295Ski/wt mice at 2 months and 1 year of age identified functional semilunar valve stenosis predominantly affecting the aortic valve with distal leaflet thickening and severe extracellular matrix (ECM) disorganization. Examination of the aortic valve at earlier postnatal timepoints demonstrated similar ECM abnormalities consistent with congenital disease. Analysis at embryonic timepoints showed a reduction in aortic valve cushion volume at embryonic day (E)13.5, predominantly affecting the non-coronary cusp (NCC). Although total cusp volume recovered by E15.5, the NCC cusp remained statistically smaller. As endothelial to mesenchymal transition (EMT)-derived cells contribute significantly to the NCC, we performed proximal outflow tract cushion explant assays and found EMT deficits in Gata4^G295Ski/wt embryos along with deficits in cell proliferation. RNA-seq analysis of E15.5 outflow tracts of mutant embryos suggested a disease state and identified changes in genes involved in ECM and cell migration as well as dysregulation of Wnt signaling. By utilizing a mouse model harboring a human disease-causing mutation, we demonstrate a novel role for GATA4 in congenital semilunar valve stenosis.

This article has an associated First Person interview with the joint first authors of the paper.

Summary: Cellular and molecular characterization of a mutant mouse, harboring a human disease-causing GATA4 variant, identifies cellular deficits in endothelial-to-mesenchymal transition and proliferation that cause abnormal valve remodeling and resultant stenosis.

Gata4 regulates hedgehog signaling and Gata6 expression for outflow tract development

Dominant mutations of Gata4, an essential cardiogenic transcription factor (TF), were known to cause outflow tract (OFT) defects in both human and mouse, but the underlying molecular mechanism was not clear. In this study, Gata4 haploinsufficiency in mice was found to result in OFT defects including double outlet right ventricle (DORV) and ventricular septum defects (VSDs). Gata4 was shown to be required for Hedgehog (Hh)-receiving progenitors within the second heart field (SHF) for normal OFT alignment. Restored cell proliferation in the SHF by knocking-down Pten failed to rescue OFT defects, suggesting that additional cell events under Gata4 regulation is important. SHF Hh-receiving cells failed to migrate properly into the proximal OFT cushion, which is associated with abnormal EMT and cell proliferation in Gata4 haploinsufficiency. The genetic interaction of Hh signaling and Gata4 is further demonstrated to be important for OFT development. Gata4 and Smo double heterozygotes displayed more severe OFT abnormalities including persistent truncus arteriosus (PTA). Restoration of Hedgehog signaling renormalized SHF cell proliferation and migration, and rescued OFT defects in Gata4 haploinsufficiency. In addition, there was enhanced Gata6 expression in the SHF of the Gata4 heterozygotes. The Gata4-responsive repressive sites were identified within 1kbp upstream of the transcription start site of Gata6 by both ChIP-qPCR and luciferase reporter assay. These results suggested a SHF regulatory network comprising of Gata4, Gata6 and Hh-signaling for OFT development.

Gata4 is an important transcription factor that regulates the development of the heart. Human possessing a single copy of Gata4 mutation display congenital heart defects (CHD), including double outlet right ventricle (DORV). DORV is an alignment problem in which both the Aorta and Pulmonary Artery originate from the right ventricle, instead of originating from the left and the right ventricles, respectively. In this study, a Gata4 mutant mouse model was used to study how Gata4 mutations cause DORV. We showed that Gata4 is required in the cardiac precursor cells for the normal alignment of the great arteries. Although Gata4 mutations inhibit the rapid increase in the cardiac precursor cell numbers, resolving this problem does not recover the normal alignment of the great arteries. It indicates that there is a migratory issue of the cardiac precursor cells as they navigate to the great arteries during development. The study further showed that a specific molecular signaling, Hh-signaling and Gata6 are responsible to the Gata4 action in the cardiac precursor cells. Importantly, over-activation of the Hh-signaling pathways rescues the DORV in the Gata4 mutant embryos. This study provides a molecular model to explain the ontogeny of a subtype of CHD.

Genetic and epigenetic regulation of cardiomyocytes in development, regeneration and disease

Embryonic and postnatal life depend on the uninterrupted function of cardiac muscle cells. These cells, termed cardiomyocytes, display many fascinating behaviors, including complex morphogenic movements, interactions with other cell types of the heart, persistent contractility and quiescence after birth. Each of these behaviors depends on complex interactions between both cardiac-restricted and widely expressed transcription factors, as well as on epigenetic modifications. Here, we review recent advances in our understanding of the genetic and epigenetic control of cardiomyocyte differentiation and proliferation during heart development, regeneration and disease. We focus on those regulators that are required for both heart development and disease, and highlight the regenerative principles that might be manipulated to restore function to the injured adult heart.

A Gata4 nuclear GFP transcriptional reporter to study endoderm and cardiac development in the mouse

The GATA zinc-finger transcription factor GATA4 is expressed in a variety of tissues during mouse embryonic development and in adult organs. These include the primitive endoderm of the blastocyst, visceral endoderm of the early post-implantation embryo, as well as lateral plate mesoderm, developing heart, liver, lung and gonads. Here, we generate a novel Gata4 targeted allele used to generate both a Gata4^H2B-GFP transcriptional reporter and a Gata4^FLAG fusion protein to analyse dynamic expression domains. We demonstrate that the Gata4^H2B-GFP transcriptional reporter faithfully recapitulates known sites of Gata4 mRNA expression and correlates with endogenous GATA4 protein levels. This reporter labels nuclei of Gata4 expressing cells and is suitable for time-lapse imaging and single cell analyses. As such, this Gata4^H2B-GFP allele will be a useful tool for studying Gata4 expression and transcriptional regulation.This article has an associated First Person interview with the first author of the paper.

Heart enhancers with deeply conserved regulatory activity are established early in zebrafish development

During the phylotypic period, embryos from different genera show similar gene expression patterns, implying common regulatory mechanisms. Here we set out to identify enhancers involved in the initial events of cardiogenesis, which occurs during the phylotypic period. We isolate early cardiac progenitor cells from zebrafish embryos and characterize 3838 open chromatin regions specific to this cell population. Of these regions, 162 overlap with conserved non-coding elements (CNEs) that also map to open chromatin regions in human. Most of the zebrafish conserved open chromatin elements tested drive gene expression in the developing heart. Despite modest sequence identity, human orthologous open chromatin regions recapitulate the spatial temporal expression patterns of the zebrafish sequence, potentially providing a basis for phylotypic gene expression patterns. Genome-wide, we discover 5598 zebrafish-human conserved open chromatin regions, suggesting that a diverse repertoire of ancient enhancers is established prior to organogenesis and the phylotypic period.

During early embryogenesis, critical cardiac specification events occur. Here the authors isolate cardiac progenitor cells from early zebrafish embryos and characterize accessible chromatin regions specific to this cell population, finding that many of these regions overlap with conserved non-coding elements that are ortholgous to accessible chromatin regions in human.