Single-cell transcriptomics uncovers a non-autonomous Tbx1-dependent genetic program controlling cardiac neural crest cell development.

Disruption of cardiac neural crest cells (CNCCs) results in congenital heart disease, yet we do not understand the cell fate dynamics as these cells differentiate to vascular smooth muscle cells. Here we performed single-cell RNA-sequencing of NCCs from the pharyngeal apparatus with the heart in control mouse embryos and when Tbx1, the gene for 22q11.2 deletion syndrome, is inactivated. We uncover three dynamic transitions of pharyngeal NCCs expressing Tbx2 and Tbx3 through differentiated CNCCs expressing cardiac transcription factors with smooth muscle genes. These transitions are altered non-autonomously by loss of Tbx1. Further, inactivation of Tbx2 and Tbx3 in early CNCCs results in aortic arch branching defects due to failed smooth muscle differentiation. Loss of Tbx1 interrupts mesoderm to CNCC cell-cell communication with upregulation and premature activation of BMP signaling and reduced MAPK signaling, as well as alteration of other signaling, and failed dynamic transitions of CNCCs leading to disruption of aortic arch artery formation and cardiac outflow tract septation.

Protocols for Investigating the Epithelial Properties of Cardiac Progenitor Cells in the Mouse Embryo.

Epithelial cardiac progenitor cells of the second heart field (SHF) contribute to growth of the vertebrate heart tube by progressive addition of cells from the dorsal pericardial wall to the cardiac poles. Perturbation of SHF development, including defects in apicobasal or planar polarity, results in shortening of the heart tube and a spectrum of congenital heart defects. Here, we provide detailed protocols for fixed section and wholemount immunofluorescence and live imaging approaches to studying the epithelial properties of cardiac progenitors in the dorsal pericardial wall during mouse heart development. Whole-embryo culture and electroporation methods are also presented, allowing for pharmacological and genetic perturbation of SHF development, as well as image analysis approaches to quantify cell features across the progenitor cell epithelium. These protocols are broadly applicable to the study of epithelia in the early embryo.

Single cell multi-omic analysis identifies a Tbx1-dependent multilineage primed population in murine cardiopharyngeal mesoderm.

The poles of the heart and branchiomeric muscles of the face and neck are formed from the cardiopharyngeal mesoderm within the pharyngeal apparatus. They are disrupted in patients with 22q11.2 deletion syndrome, due to haploinsufficiency of TBX1, encoding a T-box transcription factor. Here, using single cell RNA-sequencing, we now identify a multilineage primed population within the cardiopharyngeal mesoderm, marked by Tbx1, which has bipotent properties to form cardiac and branchiomeric muscle cells. The multilineage primed cells are localized within the nascent mesoderm of the caudal lateral pharyngeal apparatus and provide a continuous source of cardiopharyngeal mesoderm progenitors. Tbx1 regulates the maturation of multilineage primed progenitor cells to cardiopharyngeal mesoderm derivatives while restricting ectopic non-mesodermal gene expression. We further show that TBX1 confers this balance of gene expression by direct and indirect regulation of enriched genes in multilineage primed progenitors and downstream pathways, partly through altering chromatin accessibility, the perturbation of which can lead to congenital defects in individuals with 22q11.2 deletion syndrome.

A rapid review of home-based activities that can promote mental wellness during the COVID-19 pandemic.

BACKGROUND: During the COVID-19 pandemic, public health measures such as isolation, quarantine, and social distancing are needed. Some of these measures can adversely affect mental health. Activities that can be performed at home may mitigate these consequences and improve overall mental well-being. In this study, home-based activities that have potential beneficial effects on mental health were examined. METHODS: A rapid review was conducted based on a search of the following databases: MEDLINE, EMBASE, CINAHL, PyscINFO, Global Health, epistemonikos.org, covid19reviews.org, and eppi.ioe.ac.uk/covid19_map_v13.html. Eligible studies include randomized controlled trials and non-randomized studies published between 1/1/2000 and 28/05/2020 and that examined the impact of various activities on mental health outcomes in low-resource settings and contexts that lead to social isolation. Studies of activities that require mental health professionals or that could not be done at home were excluded. Two review authors performed title/abstract screening. At the full-text review stage, 25% of the potentially eligible studies were reviewed in full by two review authors; the rest were reviewed by one review author. Risk of bias assessment and data extraction were performed by one review author and checked by a second review author. The main outcome assessed was change or differences in mental health as expressed in Cohen's d; analysis was conducted following the synthesis without meta-analysis guidelines (SWiM). PROSPERO registration: CRD42020186082. RESULTS: Of 1,236 unique records identified, 160 were reviewed in full, resulting in 16 included studies. The included studies reported on the beneficial effects of exercise, yoga, progressive muscle relaxation, and listening to relaxing music. One study reported on the association between solitary religious activities and post traumatic stress disorder symptoms. While most of the included studies examined activities in group settings, particularly among individuals in prisons, the activities were described as something that can be performed at home and alone. All included studies were assessed to be at risk of bias in one or more of the bias domains examined. CONCLUSIONS: There is some evidence that certain home-based activities can promote mental wellness during the COVID-19 pandemic. Guidelines are needed to help optimize benefits while minimizing potential risks when performing these activities.

Hox-dependent coordination of mouse cardiac progenitor cell patterning and differentiation.

Perturbation of addition of second heart field (SHF) cardiac progenitor cells to the poles of the heart tube results in congenital heart defects (CHD). The transcriptional programs and upstream regulatory events operating in different subpopulations of the SHF remain unclear. Here, we profile the transcriptome and chromatin accessibility of anterior and posterior SHF sub-populations at genome-wide levels and demonstrate that Hoxb1 negatively regulates differentiation in the posterior SHF. Spatial mis-expression of Hoxb1 in the anterior SHF results in hypoplastic right ventricle. Activation of Hoxb1 in embryonic stem cells arrests cardiac differentiation, whereas Hoxb1-deficient mouse embryos display premature cardiac differentiation. Moreover, ectopic differentiation in the posterior SHF of embryos lacking both Hoxb1 and its paralog Hoxa1 results in atrioventricular septal defects. Our results show that Hoxb1 plays a key role in patterning cardiac progenitor cells that contribute to both cardiac poles and provide new insights into the pathogenesis of CHD.

T-box genes and retinoic acid signaling regulate the segregation of arterial and venous pole progenitor cells in the murine second heart field.

The arterial and venous poles of the mammalian heart are hotspots of congenital heart defects (CHD) such as those observed in 22q11.2 deletion (or DiGeorge) and Holt-Oram syndromes. These regions of the heart are derived from late differentiating cardiac progenitor cells of the Second Heart Field (SHF) located in pharyngeal mesoderm contiguous with the elongating heart tube. The T-box transcription factor Tbx1, encoded by the major 22q11.2 deletion syndrome gene, regulates SHF addition to both cardiac poles from a common progenitor population. Despite the significance of this cellular addition the mechanisms regulating the deployment of common progenitor cells to alternate cardiac poles remain poorly understood. Here we demonstrate that Tbx5, mutated in Holt-Oram syndrome and essential for venous pole development, is activated in Tbx1 expressing cells in the posterior region of the SHF at early stages of heart tube elongation. A subset of the SHF transcriptional program, including Tbx1 expression, is subsequently downregulated in Tbx5 expressing cells, generating a transcriptional boundary between Tbx1-positive arterial pole and Tbx5-positive venous pole progenitor cell populations. We show that normal downregulation of the definitive arterial pole progenitor cell program in the posterior SHF is dependent on both Tbx1 and Tbx5. Furthermore, retinoic acid (RA) signaling is required for Tbx5 activation in Tbx1-positive cells and blocking RA signaling at the time of Tbx5 activation results in atrioventricular septal defects at fetal stages. Our results reveal sequential steps of cardiac progenitor cell patterning and provide mechanistic insights into the origin of common forms of CHD.

Epithelial Properties of the Second Heart Field.

The vertebrate heart tube forms from epithelial progenitor cells in the early embryo and subsequently elongates by progressive addition of second heart field (SHF) progenitor cells from adjacent splanchnic mesoderm. Failure to maximally elongate the heart results in a spectrum of morphological defects affecting the cardiac poles, including outflow tract alignment and atrioventricular septal defects, among the most common congenital birth anomalies. SHF cells constitute an atypical apicobasally polarized epithelium with dynamic basal filopodia, located in the dorsal wall of the pericardial cavity. Recent studies have highlighted the importance of epithelial architecture and cell adhesion in the SHF, particularly for signaling events that control the progenitor cell niche during heart tube elongation. The 22q11.2 deletion syndrome gene Tbx1 regulates progenitor cell status through modulating cell shape and filopodial activity and is required for SHF contributions to both cardiac poles. Noncanonical Wnt signaling and planar cell polarity pathway genes control epithelial polarity in the dorsal pericardial wall, as progenitor cells differentiate in a transition zone at the arterial pole. Defects in these pathways lead to outflow tract shortening. Moreover, new biomechanical models of heart tube elongation have been proposed based on analysis of tissue-wide forces driving epithelial morphogenesis in the SHF, including regional cell intercalation, cell cohesion, and epithelial tension. Regulation of the epithelial properties of SHF cells is thus emerging as a key step during heart tube elongation, adding a new facet to our understanding of the mechanisms underlying both heart morphogenesis and congenital heart defects.

Epithelial tension in the second heart field promotes mouse heart tube elongation.

Extension of the vertebrate heart tube is driven by progressive addition of second heart field (SHF) progenitor cells to the poles of the heart. Defects in this process cause a spectrum of congenital anomalies. SHF cells form an epithelial layer in splanchnic mesoderm in the dorsal wall of the pericardial cavity. Here we report oriented cell elongation, polarized actomyosin distribution and nuclear YAP/TAZ in a proliferative centre in the posterior dorsal pericardial wall during heart tube extension. These parameters are indicative of mechanical stress, further supported by analysis of cell shape changes in wound assays. Time course and mutant analysis identifies SHF deployment as a source of epithelial tension. Moreover, cell division and oriented growth in the dorsal pericardial wall align with the axis of cell elongation, suggesting that epithelial tension in turn contributes to heart tube extension. Our results implicate tissue-level forces in the regulation of heart tube extension.

A positive risk approach when clients choose to live at risk: a palliative case discussion.

PURPOSE OF REVIEW: The article discusses recent approaches in the literature about clients who chose to live at risk in their homes. It argues for a positive risk-based approach and a tool to help manage risk in the home, and applies these to a hypothetical end-of-life scenario. RECENT FINDINGS: Historically, safety plans to consider risk management involved a culture of risk aversion supported by sometimes paternalistic motives intended to protect vulnerable clients. New findings in the literature engage in a process that respects the ethical principles underlying harm reduction philosophies. The literature also argues for a perspective that moves away from viewing risk as only harmful, to one that supports a positive understanding of risk as part of a client's informed choice. SUMMARY: A risk support management plan, based on a positive approach, can provide a way to both support a client's choice to live at risk, anticipate for expected complications, and inform the creation of a contingency plan to address concerns as they may arise. The added value of a structured approach like the one proposed here for risk support management plans is that it provides adequate due diligence and informed decision-making when planning for risk-taking in complex situations.

Tbx1 coordinates addition of posterior second heart field progenitor cells to the arterial and venous poles of the heart.

RATIONALE: Cardiac progenitor cells from the second heart field (SHF) contribute to rapid growth of the embryonic heart, giving rise to right ventricular and outflow tract (OFT) myocardium at the arterial pole of the heart, and atrial myocardium at the venous pole. Recent clonal analysis and cell-tracing experiments indicate that a common progenitor pool in the posterior region of the SHF gives rise to both OFT and atrial myocytes. The mechanisms regulating deployment of this progenitor pool remain unknown. OBJECTIVE: To evaluate the role of TBX1, the major gene implicated in congenital heart defects in 22q11.2 deletion syndrome patients, in posterior SHF development. METHODS AND RESULTS: Using transcriptome analysis, genetic tracing, and fluorescent dye-labeling experiments, we show that Tbx1-dependent OFT myocardium originates in Hox-expressing cells in the posterior SHF. In Tbx1 null embryos, OFT progenitor cells fail to segregate from this progenitor cell pool, leading to failure to expand the dorsal pericardial wall and altered positioning of the cardiac poles. Unexpectedly, addition of SHF cells to the venous pole of the heart is also impaired, resulting in abnormal development of the dorsal mesenchymal protrusion, and partially penetrant atrioventricular septal defects, including ostium primum defects. CONCLUSIONS: Tbx1 is required for inflow as well as OFT morphogenesis by regulating the segregation and deployment of progenitor cells in the posterior SHF. Our results provide new insights into the pathogenesis of congenital heart defects and 22q11.2 deletion syndrome phenotypes.