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1.  A Universal and Robust Integrated Platform for the Scalable Production of Human Cardiomyocytes From Pluripotent Stem Cells 
Stem Cells Translational Medicine  2015;4(12):1482-1494.
A scalable, robust, and integrated differentiation platform for large-scale production of human pluripotent stem cell-cardiomyocyte (hPSC-CM) in a stirred suspension bioreactor as a single-unit operation was developed. This platform could become a valuable tool for mass production of functional hPSC-CMs as a prerequisite for realizing their promising potential for therapeutic and industrial applications including drug discovery and toxicity assays.
Recent advances in the generation of cardiomyocytes (CMs) from human pluripotent stem cells (hPSCs), in conjunction with the promising outcomes from preclinical and clinical studies, have raised new hopes for cardiac cell therapy. We report the development of a scalable, robust, and integrated differentiation platform for large-scale production of hPSC-CM aggregates in a stirred suspension bioreactor as a single-unit operation. Precise modulation of the differentiation process by small molecule activation of WNT signaling, followed by inactivation of transforming growth factor-β and WNT signaling and activation of sonic hedgehog signaling in hPSCs as size-controlled aggregates led to the generation of approximately 100% beating CM spheroids containing virtually pure (∼90%) CMs in 10 days. Moreover, the developed differentiation strategy was universal, as demonstrated by testing multiple hPSC lines (5 human embryonic stem cell and 4 human inducible PSC lines) without cell sorting or selection. The produced hPSC-CMs successfully expressed canonical lineage-specific markers and showed high functionality, as demonstrated by microelectrode array and electrophysiology tests. This robust and universal platform could become a valuable tool for the mass production of functional hPSC-CMs as a prerequisite for realizing their promising potential for therapeutic and industrial applications, including drug discovery and toxicity assays.
Recent advances in the generation of cardiomyocytes (CMs) from human pluripotent stem cells (hPSCs) and the development of novel cell therapy strategies using hPSC-CMs (e.g., cardiac patches) in conjunction with promising preclinical and clinical studies, have raised new hopes for patients with end-stage cardiovascular disease, which remains the leading cause of morbidity and mortality globally. In this study, a simplified, scalable, robust, and integrated differentiation platform was developed to generate clinical grade hPSC-CMs as cell aggregates under chemically defined culture conditions. This approach resulted in approximately 100% beating CM spheroids with virtually pure (∼90%) functional cardiomyocytes in 10 days from multiple hPSC lines. This universal and robust bioprocessing platform can provide sufficient numbers of hPSC-CMs for companies developing regenerative medicine technologies to rescue, replace, and help repair damaged heart tissues and for pharmaceutical companies developing advanced biologics and drugs for regeneration of lost heart tissue using high-throughput technologies. It is believed that this technology can expedite clinical progress in these areas to achieve a meaningful impact on improving clinical outcomes, cost of care, and quality of life for those patients disabled and experiencing heart disease.
PMCID: PMC4675501  PMID: 26511653
Human pluripotent stem cells; Embryonic stem; Induced pluripotent stem; Cardiomyocytes; Directed differentiation; Cell therapy; Small molecules; Bioreactor
2.  NKX2-5 mutations causative for congenital heart disease retain functionality and are directed to hundreds of targets 
eLife  null;4:e06942.
We take a functional genomics approach to congenital heart disease mechanism. We used DamID to establish a robust set of target genes for NKX2-5 wild type and disease associated NKX2-5 mutations to model loss-of-function in gene regulatory networks. NKX2-5 mutants, including those with a crippled homeodomain, bound hundreds of targets including NKX2-5 wild type targets and a unique set of "off-targets", and retained partial functionality. NKXΔHD, which lacks the homeodomain completely, could heterodimerize with NKX2-5 wild type and its cofactors, including E26 transformation-specific (ETS) family members, through a tyrosine-rich homophilic interaction domain (YRD). Off-targets of NKX2-5 mutants, but not those of an NKX2-5 YRD mutant, showed overrepresentation of ETS binding sites and were occupied by ETS proteins, as determined by DamID. Analysis of kernel transcription factor and ETS targets show that ETS proteins are highly embedded within the cardiac gene regulatory network. Our study reveals binding and activities of NKX2-5 mutations on WT target and off-targets, guided by interactions with their normal cardiac and general cofactors, and suggest a novel type of gain-of-function in congenital heart disease.
eLife digest
Many genes working within large gene networks influence the development of heart muscle cells in humans and other animals. The activity of these genes is controlled in part by proteins called transcription factors, which bind to DNA and act as molecular switches. One transcription factor that is particularly important for the development of heart muscle cells is called NKX2-5.
Mice lacking NKX2-5 have abnormal hearts and many humans who are born with congenital heart disease carry mutations in the gene that encodes this protein. Many of these mutations alter a section of the protein called the homeodomain, and therefore interfere with the ability of NKX2-5 to bind to DNA or associate with other important cardiac proteins called cofactors. However, it is not clear how such mutations alter the behaviour of NKX2-5 across all of its targets.
Bouveret et al. have now used a technique called ‘DNA adenine methyltransferase identification’ to study how NKX2-5 interacts with other proteins and DNA. The experiments found that, as expected, the mutant NKX2-5 proteins were unable to associate with many of the usual gene and protein targets of normal NKX2-5. However, the mutant proteins were still able to bind to some of their usual targets, plus many other targets that the normal NKX2-5 protein was not able to bind to.
A particular NKX2-5 mutant protein that the experiments analysed was missing the entire homeodomain, yet it was still able to associate with the normal NKX2-5 protein and bind to cofactors that help NKX2-5 to find its usual targets. This finding led Bouveret et al. to discover the role of a section of the NKX2-5 protein called the tyrosine-rich domain, which in the absence of the homeodomain can direct interactions of NKX2-5 with itself and its cofactors.
Bouveret et al.'s findings suggest that protein cofactors of NKX2-5 help mutant NKX2-5 proteins retain some of their normal activities, but also direct the mutant proteins to abnormal gene targets, which could contribute to congenital heart disease. The next steps are to carry out experiments in animals to confirm these findings, and to understand the activities of mutant NKX2-5 and other mutant transcription factors across the whole genome. This could lead to new therapeutic approaches to treat congenital heart disease and other conditions.
PMCID: PMC4548209  PMID: 26146939
cardiogenesis; transcription factors; genetic diseases; mouse
3.  Genetic Networks Governing Heart Development 
Animal genomes contain a code for construction of the body plan from a fertilized egg. Understanding how genome information is deciphered to create the complex multilayered regulatory systems that drive organismal development, and which become altered in disease, is one of the greatest challenges in the biological sciences. The development of methods that effectively represent and communicate the complexity inherent in gene regulatory networks remains a major barrier. This review introduces the philosophy of systems biology and discusses recent progress in understanding the development of the heart at a systems biology level.
Systems biology tools are useful for understanding complex heart developmental networks and for elucidating the impacts of genetic mutations in heart disease.
PMCID: PMC4208705  PMID: 25280899
4.  A rapid co-culture stamping device for studying intercellular communication 
Scientific Reports  2016;6:35618.
Regulation of tissue development and repair depends on communication between neighbouring cells. Recent advances in cell micro-contact printing and microfluidics have facilitated the in-vitro study of homotypic and heterotypic cell-cell interaction. Nonetheless, these techniques are still complicated to perform and as a result, are seldom used by biologists. We report here development of a temporarily sealed microfluidic stamping device which utilizes a novel valve design for patterning two adherent cell lines with well-defined interlacing configurations to study cell-cell interactions. We demonstrate post-stamping cell viability of >95%, the stamping of multiple adherent cell types, and the ability to control the seeded cell density. We also show viability, proliferation and migration of cultured cells, enabling analysis of co-culture boundary conditions on cell fate. We also developed an in-vitro model of endothelial and cardiac stem cell interactions, which are thought to regulate coronary repair after myocardial injury. The stamp is fabricated using microfabrication techniques, is operated with a lab pipettor and uses very low reagent volumes of 20 μl with cell injection efficiency of >70%. This easy-to-use device provides a general strategy for micro-patterning of multiple cell types and will be important for studying cell-cell interactions in a multitude of applications.
PMCID: PMC5067516  PMID: 27752145
5.  Prediction and validation of protein–protein interactors from genome-wide DNA-binding data using a knowledge-based machine-learning approach 
Open Biology  2016;6(9):160183.
The ability to accurately predict the DNA targets and interacting cofactors of transcriptional regulators from genome-wide data can significantly advance our understanding of gene regulatory networks. NKX2-5 is a homeodomain transcription factor that sits high in the cardiac gene regulatory network and is essential for normal heart development. We previously identified genomic targets for NKX2-5 in mouse HL-1 atrial cardiomyocytes using DNA-adenine methyltransferase identification (DamID). Here, we apply machine learning algorithms and propose a knowledge-based feature selection method for predicting NKX2-5 protein : protein interactions based on motif grammar in genome-wide DNA-binding data. We assessed model performance using leave-one-out cross-validation and a completely independent DamID experiment performed with replicates. In addition to identifying previously described NKX2-5-interacting proteins, including GATA, HAND and TBX family members, a number of novel interactors were identified, with direct protein : protein interactions between NKX2-5 and retinoid X receptor (RXR), paired-related homeobox (PRRX) and Ikaros zinc fingers (IKZF) validated using the yeast two-hybrid assay. We also found that the interaction of RXRα with NKX2-5 mutations found in congenital heart disease (Q187H, R189G and R190H) was altered. These findings highlight an intuitive approach to accessing protein–protein interaction information of transcription factors in DNA-binding experiments.
PMCID: PMC5043580  PMID: 27683156
machine learning; protein–protein interactions; transcription factors; gene regulatory networks
6.  Pressure Overload by Transverse Aortic Constriction Induces Maladaptive Hypertrophy in a Titin-Truncated Mouse Model 
BioMed Research International  2015;2015:163564.
Mutations in the giant sarcomeric protein titin (TTN) are a major cause for inherited forms of dilated cardiomyopathy (DCM). We have previously developed a mouse model that imitates a TTN truncation mutation we found in a large pedigree with DCM. While heterozygous Ttn knock-in mice do not display signs of heart failure under sedentary conditions, they recapitulate the human phenotype when exposed to the pharmacological stressor angiotensin II or isoproterenol. In this study we investigated the effects of pressure overload by transverse aortic constriction (TAC) in heterozygous (Het) Ttn knock-in mice. Two weeks after TAC, Het mice developed marked impairment of left ventricular ejection fraction (p < 0.05), while wild-type (WT) TAC mice did not. Het mice also trended toward increased ventricular end diastolic pressure and volume compared to WT littermates. We found an increase in histologically diffuse cardiac fibrosis in Het compared to WT in TAC mice. This study shows that a pattern of DCM can be induced by TAC-mediated pressure overload in a TTN-truncated mouse model. This model enlarges our arsenal of cardiac disease models, adding a valuable tool to understand cardiac pathophysiological remodeling processes and to develop therapeutic approaches to combat heart failure.
PMCID: PMC4609346  PMID: 26504781
8.  Bioengineering and Stem Cell Technology in the Treatment of Congenital Heart Disease 
Journal of Clinical Medicine  2015;4(4):768-781.
Congenital heart disease places a significant burden on the individual, family and community despite significant advances in our understanding of aetiology and treatment. Early research in ischaemic heart disease has paved the way for stem cell technology and bioengineering, which promises to improve both structural and functional aspects of disease. Stem cell therapy has demonstrated significant improvements in cardiac function in adults with ischaemic heart disease. This finding, together with promising case studies in the paediatric setting, demonstrates the potential for this treatment in congenital heart disease. Furthermore, induced pluripotent stems cell technology, provides a unique opportunity to address aetiological, as well as therapeutic, aspects of disease.
PMCID: PMC4470166  PMID: 26239354
congenital heart disease; hypoplastic left heart; inducible pluripotential stem cells; bioengineered myocardium
9.  Introduction to the Special Issue on Heart Regeneration and Rejuvenation 
Stem cell research  2014;13(0):521-522.
PMCID: PMC4268077  PMID: 25459518
10.  Lack of Genetic Interaction between Tbx20 and Tbx3 in Early Mouse Heart Development 
PLoS ONE  2013;8(7):e70149.
Members of the T-box family of transcription factors are important regulators orchestrating the complex regionalization of the developing mammalian heart. Individual mutations in Tbx20 and Tbx3 cause distinct congenital heart abnormalities in the mouse: Tbx20 mutations result in failure of heart looping, developmental arrest and lack of chamber differentiation, while hearts of Tbx3 mutants progress further, loop normally but show atrioventricular convergence and outflow tract defects. The two genes have overlapping areas of expression in the atrioventricular canal and outflow tract of the heart but their potential genetic interaction has not been previously investigated. In this study we produced compound mutants to investigate potential genetic interactions at the earliest stages of heart development. We find that Tbx20; Tbx3 double heterozygous mice are viable and fertile with no apparent abnormalities, while double homozygous mutants are embryonic lethal by midgestation. Double homozygous mutant embryos display abnormal cardiac morphogenesis, lack of heart looping, expression patterns of cardiac genes and time of death that are indistinguishable from Tbx20 homozygous mutants. Prior to death, the double homozygotes show an overall developmental delay similar to Tbx3 homozygous mutants. Thus the effects of Tbx20 are epistatic to Tbx3 in the heart but Tbx3 is epistatic to Tbx20 with respect to developmental delay.
PMCID: PMC3723716  PMID: 23936153
11.  CompGO: an R package for comparing and visualizing Gene Ontology enrichment differences between DNA binding experiments 
BMC Bioinformatics  2015;16:275.
Gene ontology (GO) enrichment is commonly used for inferring biological meaning from systems biology experiments. However, determining differential GO and pathway enrichment between DNA-binding experiments or using the GO structure to classify experiments has received little attention.
Herein, we present a bioinformatics tool, CompGO, for identifying Differentially Enriched Gene Ontologies, called DiEGOs, and pathways, through the use of a z-score derivation of log odds ratios, and visualizing these differences at GO and pathway level. Through public experimental data focused on the cardiac transcription factor NKX2-5, we illustrate the problems associated with comparing GO enrichments between experiments using a simple overlap approach.
We have developed an R/Bioconductor package, CompGO, which implements a new statistic normally used in epidemiological studies for performing comparative GO analyses and visualizing comparisons from .BED data containing genomic coordinates as well as gene lists as inputs. We justify the statistic through inclusion of experimental data and compare to the commonly used overlap method. CompGO is freely available as a R/Bioconductor package enabling easy integration into existing pipelines and is available at: packages/release/bioc/html/CompGO.html
PMCID: PMC4557902  PMID: 26329719
12.  Functional Characterization of a Novel Mutation in NKX2-5 Associated with Congenital Heart Disease and Adult-Onset Cardiomyopathy 
Circulation. Cardiovascular genetics  2013;6(3):10.1161/CIRCGENETICS.113.000057.
The transcription factor NKX2-5 is crucial for heart development and mutations in this gene have been implicated in diverse congenital heart diseases (CHD) and conduction defects (CD) in mouse models and humans. Whether NKX2-5 mutations have a role in adult-onset heart disease is unknown.
Methods and Results
Mutation screening was performed in 220 probands with adult-onset dilated cardiomypathy (DCM). Six NKX2-5 coding sequence variants were identified, including 3 non-synonymous variants. A novel heterozygous mutation, I184M, located within the NKX2-5 homeodomain (HD), was identified in one family. A subset of family members had CHD, but there was an unexpectedly high prevalence of DCM. Functional analysis of I184M in vitro demonstrated a striking increase in protein expression when transfected into COS-7 cells or HL-1 cardiomyocytes, due to reduced degradation by the ubiquitin-proteasome system (UPS). In functional assays, DNA binding activity of I184M was reduced, resulting in impaired activation of target genes, despite increased expression levels of mutant protein.
Certain NKX2-5 HD mutations show abnormal protein degradation via the UPS and partially impaired transcriptional activity. We propose that this class of mutation can impair heart development and mature heart function, and contribute to NKX2-5-related cardiomyopathies with graded severity.
PMCID: PMC3816146  PMID: 23661673
dilated cardiomyopathy; transcription factors; gene mutations; ubiquitin-proteasome system; NKX2-5
13.  Antisense-mediated exon skipping: a therapeutic strategy for titin-based dilated cardiomyopathy 
EMBO Molecular Medicine  2015;7(5):562-576.
Frameshift mutations in the TTN gene encoding titin are a major cause for inherited forms of dilated cardiomyopathy (DCM), a heart disease characterized by ventricular dilatation, systolic dysfunction, and progressive heart failure. To date, there are no specific treatment options for DCM patients but heart transplantation. Here, we show the beneficial potential of reframing titin transcripts by antisense oligonucleotide (AON)-mediated exon skipping in human and murine models of DCM carrying a previously identified autosomal-dominant frameshift mutation in titin exon 326. Correction of TTN reading frame in patient-specific cardiomyocytes derived from induced pluripotent stem cells rescued defective myofibril assembly and stability and normalized the sarcomeric protein expression. AON treatment in Ttn knock-in mice improved sarcomere formation and contractile performance in homozygous embryos and prevented the development of the DCM phenotype in heterozygous animals. These results demonstrate that disruption of the titin reading frame due to a truncating DCM mutation can be restored by exon skipping in both patient cardiomyocytes in vitro and mouse heart in vivo, indicating RNA-based strategies as a potential treatment option for DCM.
PMCID: PMC4492817  PMID: 25759365
dilated cardiomyopathy; exon skipping; induced pluripotent stem cells; titin
14.  Cardiogenic Genes Expressed in Cardiac Fibroblasts Contribute to Heart Development and Repair 
Circulation research  2014;114(9):1422-1434.
Cardiac fibroblasts are critical to proper heart function through multiple interactions with the myocardial compartment but appreciation of their contribution has suffered from incomplete characterization and lack of cell-specific markers.
To generate an unbiased comparative gene expression profile of the cardiac fibroblast pool, identify and characterize the role of key genes in cardiac fibroblast function, and determine their contribution to myocardial development and regeneration.
Methods and Results
High-throughput cell surface and intracellular profiling of cardiac and tail fibroblasts identified canonical MSC and a surprising number of cardiogenic genes, some expressed at higher levels than in whole heart. Whilst genetically marked fibroblasts contributed heterogeneously to interstitial but not cardiomyocyte compartments in infarcted hearts, fibroblast-restricted depletion of one highly expressed cardiogenic marker, Tbx20, caused marked myocardial dysmorphology and perturbations in scar formation upon myocardial infarction.
The surprising transcriptional identity of cardiac fibroblasts, the adoption of cardiogenic gene programs and direct contribution to cardiac development and repair provokes alternative interpretations for studies on more specialized cardiac progenitors, offering a novel perspective for reinterpreting cardiac regenerative therapies.
PMCID: PMC4083003  PMID: 24650916
Heart; fibroblast; transcription factors; transcriptional network; cardiac fibroblasts
15.  Nkx2-5 Mediates Differential Cardiac Differentiation Through Interaction with Hoxa10 
Stem Cells and Development  2013;22(15):2211-2220.
The regulation of cardiac differentiation is complex and incompletely understood. Recent studies have documented that Nkx2-5-positive cells are not limited to the cardiac lineage, but can give rise to endothelial and smooth muscle lineages. Other work has elucidated that, in addition to promoting cardiac development, Nkx2-5 plays a larger role in mesodermal patterning although the transcriptional networks that govern this developmental patterning are undefined. By profiling early Nkx2-5-positive progenitor cells, we discovered that the progenitor pools of the bisected cardiac crescent are differentiating asynchronously. This asymmetry requires Nkx2-5 as it is lost in the Nkx2-5 mutant. Surprisingly, the posterior Hox genes Hoxa9 and Hoxa10 were expressed on the right side of the cardiac crescent, independently of Nkx2-5. We describe a novel, transient, and asymmetric cardiac-specific expression pattern of the posterior Hox genes, Hoxa9 and Hoxa10, and utilize the embryonic stem cell/embryoid body (ES/EB) model system to illustrate that Hoxa10 impairs cardiac differentiation. We suggest a model whereby Hoxa10 cooperates with Nkx2-5 to regulate the timing of cardiac mesoderm differentiation.
PMCID: PMC3715789  PMID: 23477547
16.  Heart field origin of great vessel precursors relies on nkx2.5-mediated vasculogenesis 
Nature cell biology  2013;15(11):1362-1369.
The pharyngeal arch arteries (PAAs) are transient embryonic blood vessels that make indispensable contributions to the carotid arteries and great vessels of the heart, including the aorta and pulmonary artery1, 2. During embryogenesis, the PAAs appear in a craniocaudal sequence to connect pre-existing segments of the primitive circulation after de novo vasculogenic assembly from angioblast precursors3, 4. Despite the unique spatiotemporal characteristics of PAA development, the embryonic origins of PAA angioblasts and the genetic factors regulating their emergence remain unknown. Here, we identify the embryonic source of PAA endothelium as nkx2.5+ progenitors in lateral plate mesoderm long considered to adopt cell fates within the heart exclusively5, 6. Further, we report that PAA endothelial differentiation relies on Nkx2.5, a canonical cardiac transcription factor not previously implicated in blood vessel formation. Together, these studies reveal the heart field origin of PAA endothelium and attribute a novel vasculogenic function to the cardiac transcription factor nkx2.5 during great vessel precursor development.
PMCID: PMC3864813  PMID: 24161929
17.  Precardiac deletion of Numb and Numblike reveals renewal of cardiac progenitors 
eLife  2014;3:e02164.
Cardiac progenitor cells (CPCs) must control their number and fate to sustain the rapid heart growth during development, yet the intrinsic factors and environment governing these processes remain unclear. Here, we show that deletion of the ancient cell-fate regulator Numb (Nb) and its homologue Numblike (Nbl) depletes CPCs in second pharyngeal arches (PA2s) and is associated with an atrophic heart. With histological, flow cytometric and functional analyses, we find that CPCs remain undifferentiated and expansive in the PA2, but differentiate into cardiac cells as they exit the arch. Tracing of Nb- and Nbl-deficient CPCs by lineage-specific mosaicism reveals that the CPCs normally populate in the PA2, but lose their expansion potential in the PA2. These findings demonstrate that Nb and Nbl are intrinsic factors crucial for the renewal of CPCs in the PA2 and that the PA2 serves as a microenvironment for their expansion.
eLife digest
Human embryos contain cells called ‘cardiac progenitor cells’ that serve as the building blocks to make the heart. Cardiac progenitor cells, or CPCs for short, initially move into areas of the embryo called the first and second heart fields, and then undergo a change to become specific types of heart cells: such as cardiac muscle cells. However, it is not known if CPCs are maintained during the development of the heart.
Now, Shenje, Andersen et al. have shown that Numb and Numblike—two proteins that are needed for the development of nerve cells—are also involved in the development of the heart. Mouse embryos without the genes for Numb and Numblike failed to develop hearts normally; and these mutants also had fewer CPCs in the ‘second pharyngeal arch’: a part of the embryo that becomes the sides and front of the neck. Experiments on wild-type mice showed that the CPCs multiplied within this arch, and then changed into specific heart cells as they left this structure. Furthermore, mixing CPCs in a petri dish with cells taken from this arch encouraged the CPCs to multiply without changing into specific cell types.
To investigate the importance of these two proteins further, Shenje, Andersen et al. engineered ‘chimeric’ mice in which some CPCs contained the Numb and Numblike genes and other CPCs did not. In most of these chimeric mice, the hearts developed normally, but the CPCs without the Numb or Numblike genes failed to multiply in the second pharyngeal arch. This shows that these genes must be present within an individual CPC to regulate the multiplication of that cell within this arch.
By uncovering how problems with the maintenance of CPCs can lead to heart defects—a very common birth defect in humans—this work may lead to new ways to prevent or treat congenital heart disease. Furthermore, identifying the other factors or mechanisms that can allow the long-term maintenance of CPCs in the laboratory will be crucial for research into heart regeneration, and for CPC-based treatments to repair the heart.
PMCID: PMC4007206  PMID: 24843018
cardiac progenitor; self-renewal; niche; numb; microenvironment; heart; mouse
18.  Nkx2-5+Islet1+ mesenchymal precursors generate distinct spleen stromal cell subsets and participate in restoring stromal network integrity 
Immunity  2013;38(4):782-791.
Lymphoid organ stromal cells comprise different subsets whose origin remains unknown. Herein, we exploit a genetic lineage-tracing approach to show that splenic fibroblastic reticular cells (FRCs), follicular dendritic cells (FDCs), marginal reticular cells (MRCs), and mural cells, but not endothelial cells, originated from embryonic mesenchymal progenitors of the Nkx2-5+Islet1+ lineage. This lineage included embryonic mesenchymal cells with lymphoid tissue organizer (LTo) activity capable of supporting ectopic lymphoid-like structures, and a subset of resident spleen stromal cells that proliferated and regenerated the splenic stromal microenvironment following resolution of a viral infection. These findings identify progenitor cells that generate stromal diversity in spleen development and repair, and suggest the existence of multipotent stromal progenitors in the adult spleen with regenerative capacity.
PMCID: PMC3652017  PMID: 23601687
19.  A gain-of-function TBX20 mutation causes congenital atrial septal defects, patent foramen ovale and cardiac valve defects 
Journal of Medical Genetics  2010;47(4):230-235.
Ostium secundum atrial septal defects (ASDII) account for approximately 10% of all congenital heart defects (CHD), and mutations in cardiac transcription factors, including TBX20, were identified as an underlying cause for ASDII. However, very little is known about disease penetrance in families and functional consequences of inherited TBX20 mutations.
The coding region of TBX20 was directly sequenced in 170 ASDII patients. Functional consequences of one novel mutation were investigated by surface plasmon resonance, CD spectropolarymetry, fluorescence spectrophotometry, luciferase assay and chromatin immunoprecipitation.
We found a novel mutation in a highly conserved residue in the T-box DNA binding domain (I121M) segregating with CHD in a three generation kindred. Four mutation carriers revealed cardiac phenotypes in terms of cribriform ASDII, large patent foramen ovale or cardiac valve defects. Interestingly, tertiary hydrophobic interactions within the mutant TBX20 T-box were significantly altered leading to a more dynamic structure of the protein. Moreover, Tbx20-I121M resulted in a significantly enhanced transcriptional activity, which was further increased in the presence of co-transcription factors GATA4/5 and NKX2-5. Occupancy of DNA binding sites on target genes was also increased.
We suggest that TBX20-I121M adopts a more fluid tertiary structure leading to enhanced interactions with cofactors and more stable transcriptional complexes on target DNA sequences. Our data, combined with that of others, suggest that human ASDII may be related to loss-of-function as well as gain-of-function TBX20 mutations.
PMCID: PMC2981023  PMID: 19762328
Congenital heart defect; atrial septal defect; patent foramen ovale; TBX20; cardiovascular medicine; clinical genetics; molecular genetics
20.  Hemogenic endocardium contributes to transient definitive hematopoiesis 
Nature communications  2013;4:1564.
Hematopoietic cells arise from spatiotemporally restricted domains in the developing embryo. Although studies of non-mammalian animal and in vitro embryonic stem cell models suggest a close relationship among cardiac, endocardial, and hematopoietic lineages, it remains unknown whether the mammalian heart tube serves as a hemogenic organ akin to the dorsal aorta. Here we examine the hemogenic activity of the developing endocardium. Mouse heart explants generate myeloid and erythroid colonies in the absence of circulation. Hemogenic activity arises from a subset of endocardial cells in the outflow cushion and atria earlier than in the aorta-gonad-mesonephros region, and is transient and definitive in nature. Interestingly, key cardiac transcription factors, Nkx2-5 and Isl1, are expressed in and required for the hemogenic population of the endocardium. Together, these data suggest that a subset of endocardial/endothelial cells expressing cardiac markers serve as a de novo source for transient definitive hematopoietic progenitors.
PMCID: PMC3612528  PMID: 23463007
21.  Congenital Asplenia in Mice and Humans with Mutations in a Pbx/Nkx2-5/p15 Module 
Developmental Cell  2012;22(5):913-926.
The molecular determinants of spleen organogenesis and the etiology of isolated congenital asplenia (ICA), a life-threatening human condition, are unknown. We previously reported that Pbx1 deficiency causes organ growth defects including asplenia. Here, we show that mice with splenic mesenchyme-specific Pbx1 inactivation exhibit hyposplenia. Moreover, the loss of Pbx causes down-regulation of Nkx2-5 and derepression of p15Ink4b in spleen mesenchymal progenitors, perturbing the cell cycle. Removal of p15Ink4b in Pbx1 spleen-specific mutants partially rescues spleen growth. By whole-exome sequencing of a multiplex kindred with ICA, we identify a heterozygous missense mutation (P236H) in NKX2-5 showing reduced transactivation in vitro. This study establishes that a Pbx/Nkx2-5/p15 regulatory module is essential for spleen development.
PMCID: PMC3356505  PMID: 22560297
Spleen; Organ growth; Human Isolated Congenital Asplenia; Cell cycle; Pbx; p15Ink4b; Nkx2-5
22.  Adult Cardiac-Resident MSC-like Stem Cells with a Proepicardial Origin 
Cell stem cell  2011;9(6):527-540.
Colony-forming units – fibroblast (CFU-Fs), analogous to those giving rise to bone marrow (BM) mesenchymal stem cells (MSCs), are present in many organs, although the relationship between BM and organ-specific CFU-Fs in homeostasis and tissue repair is unknown. Here we describe a population of adult cardiac-resident CFU-Fs (cCFU-Fs) that occupy a perivascular, adventitial niche and show broad trans-germ layer potency in vitro and in vivo. CRE lineage tracing and embryo analysis demonstrated a proepicardial origin for cCFU-Fs. Furthermore, in BM transplantation chimeras, we found no interchange between BM and cCFU-Fs after aging, myocardial infarction, or BM stem cell mobilization. BM and cardiac and aortic CFU-Fs had distinct CRE lineage signatures, indicating that they arise from different progenitor beds during development. These diverse origins for CFU-Fs suggest an underlying basis for differentiation biases seen in different CFU-F populations, and could also influence their capacity for participating in tissue repair.
PMCID: PMC3652240  PMID: 22136928
23.  Rotary ATPases 
Bioarchitecture  2013;3(1):2-12.
Rotary ATPases are molecular rotary motors involved in biological energy conversion. They either synthesize or hydrolyze the universal biological energy carrier adenosine triphosphate. Recent work has elucidated the general architecture and subunit compositions of all three sub-types of rotary ATPases. Composite models of the intact F-, V- and A-type ATPases have been constructed by fitting high-resolution X-ray structures of individual subunits or sub-complexes into low-resolution electron densities of the intact enzymes derived from electron cryo-microscopy. Electron cryo-tomography has provided new insights into the supra-molecular arrangement of eukaryotic ATP synthases within mitochondria and mass-spectrometry has started to identify specifically bound lipids presumed to be essential for function. Taken together these molecular snapshots show that nano-scale rotary engines have much in common with basic design principles of man made machines from the function of individual “machine elements” to the requirement of the right “fuel” and “oil” for different types of motors.
PMCID: PMC3639240  PMID: 23369889
biological motors; rotary motors; energy conversion; ATP synthase; vacuolar ATPase; A-type ATPase; structural biology; X-ray crystallography; electron microscopy
24.  Combined Mutation Screening of NKX2-5, GATA4, and TBX5 in Congenital Heart Disease: Multiple Heterozygosity and Novel Mutations 
Congenital heart disease  2011;7(2):151-159.
Variants of several genes encoding transcription modulators, signal transduction, and structural proteins are known to cause Mendelian congenital heart disease (CHD). NKX2-5 and GATA4 were the first CHD-causing genes identified by linkage analysis in large affected families. Mutations of TBX5 cause Holt–Oram syndrome, which includes CHD as a clinical feature. All three genes have a well-established role in cardiac development.
In order to investigate the possible role of multiple mutations in CHD, a combined mutation screening was performed in NKX2-5, GATA4, and TBX5 in the same patient cohort. Samples from a cohort of 331 CHD patients were analyzed by polymerase chain reaction, double high-performance liquid chromatography and sequencing in order to identify changes in the NKX2-5, GATA4, and TBX5 genes.
Two cases of multiple heterozygosity of putative disease-causing mutations were identified. One patient was found with a novel L122P NKX2-5 mutation in combination with the private A1443D mutation of MYH6. A patient heterozygote for a D425N GATA4 mutation carries also a private mutation of the MYH6 gene (V700M).
In addition to reporting two novel mutations of NKX2-5 in CHD, we describe families where multiple individual mutations seem to have an additive effect over the pathogenesis of CHD. Our findings highlight the usefulness of multiple gene mutational analysis of large CHD cohorts.
PMCID: PMC3370385  PMID: 22011241
Congenital Heart Disease; Mutations; Multiple Heterozygosity
25.  Nkx2-5 Represses Gata1 Gene Expression and Modulates the Cellular Fate of Cardiac Progenitors during Embryogenesis 
Circulation  2011;123(15):1633-1641.
Recent studies suggest that the hematopoietic and cardiac lineages have close ontogenic origins, and that an early mesodermal cell population has the potential to differentiate into both lineages. Studies also suggest that specification of these lineages is inversely regulated. However, the transcriptional networks that govern the cell fate specification of these progenitors are incompletely defined.
Methods and Results
Here, we show that Nkx2-5 regulates the hematopoietic/erythroid fate of the mesoderm precursors early during cardiac morphogenesis. Utilizing transgenic technologies to isolate Nkx2-5 expressing cells, we observed an induction of the erythroid molecular program, including Gata1, in the Nkx2-5 null embryos. We further observed that overexpression of Nkx2-5 using an Nkx2-5-inducible embryonic stem (ES) cell system significantly repressed Gata1 gene expression and suppressed the hematopoietic/erythroid potential but not the endothelial potential of the ES cells. This suppression was cell-autonomous and was partially rescued by overexpressing Gata1. In addition, we demonstrated that Nkx2-5 binds to the Gata1 gene enhancer and represses the transcriptional activity of the Gata1 gene.
Our results demonstrate that the hematopoietic/erythroid cell fate is suppressed via Nkx2-5 during mesodermal fate determination and that the Gata1 gene is one of the targets that are suppressed by Nkx2-5.
PMCID: PMC3110259  PMID: 21464046
Nkx2-5; Gata1; cardiac progenitors; gene regulation

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