Growth factor-induced activation of MSK2 leads to phosphorylation of H3K9me2S10 and corresponding changes in gene expression

Extracellular signals are transmitted through kinase cascades to modulate gene expression, but it remains unclear how epigenetic changes regulate this response. Here, we provide evidence that growth factor-stimulated changes in the transcript levels of many responsive genes are accompanied by increases in histone phosphorylation levels, specifically at histone H3 serine-10 when the adjacent lysine-9 is dimethylated (H3K9me2S10). Imaging and proteomic approaches show that epidermal growth factor (EGF) stimulation results in H3K9me2S10 phosphorylation, which occurs in genomic regions enriched for regulatory enhancers of EGF-responsive genes. We also demonstrate that the EGF-induced increase in H3K9me2S10ph is dependent on the nuclear kinase MSK2, and this subset of EGF-induced genes is dependent on MSK2 for transcription. Together, our work indicates that growth factor-induced changes in chromatin state can mediate the activation of downstream genes.

Emerging mRNA therapies for cardiac fibrosis

Cardiac fibrosis remains an unmet clinical need that has so far proven difficult to eliminate using current therapies. As such, novel technologies are needed that can target the pathological fibroblasts responsible for fibrosis and adverse tissue remodeling. mRNA encapsulated in lipid nanoparticles (LNPs) is an emerging technology that could offer a solution to this problem. Indeed, this strategy has already shown clinical success with the mRNA COVID-19 vaccines. In this AJP perspective, we discuss how this technology can be leveraged to specifically target cardiac fibrosis via several complementary strategies. First, we discuss the successful preclinical studies in a mouse model of cardiac injury to use T cell-targeted LNPs to produce anti-fibroblast chimeric antigen receptor T (CAR T) cells in vivo that could effectively reduce cardiac fibrosis. Next, we discuss how these T cell-targeted LNPs could be used to generate T regulatory cells (T-regs), which could migrate to areas of active fibrosis and dampen inflammation through paracrine effects as an alternative to active fibroblast killing by CAR T cells. Finally, we conclude with thoughts on directly targeting pathological fibroblasts to deliver RNAs that could interfere with fibroblast activation and activity. We hope this discussion serves as a catalyst for finding approaches that harness the power of mRNA and LNPs to eliminate cardiac fibrosis and treat other fibrotic diseases amenable to such interventions.NEW & NOTEWORTHY Cardiac fibrosis has few specific interventions available for effective treatment. mRNA encapsulated in lipid nanoparticles could provide a novel solution for treating cardiac fibrosis. This AJP perspective discusses what possible strategies could rely on this technology, from in vivo-produced CAR T cells that kill pathological fibroblasts to in vivo-produced T regulatory cells that dampen the concomitant profibrotic inflammatory cells contributing to remodeling, directly targeting fibroblasts and eliminating them or silencing profibrotic pathways.

CAR T therapy beyond cancer: the evolution of a living drug

Engineering a patient's own T cells to selectively target and eliminate tumour cells has cured patients with untreatable haematologic cancers. These results have energized the field to apply chimaeric antigen receptor (CAR) T therapy throughout oncology. However, evidence from clinical and preclinical studies underscores the potential of CAR T therapy beyond oncology in treating autoimmunity, chronic infections, cardiac fibrosis, senescence-associated disease and other conditions. Concurrently, the deployment of new technologies and platforms provides further opportunity for the application of CAR T therapy to noncancerous pathologies. Here we review the rationale behind CAR T therapy, current challenges faced in oncology, a synopsis of preliminary reports in noncancerous diseases, and a discussion of relevant emerging technologies. We examine potential applications for this therapy in a wide range of contexts. Last, we highlight concerns regarding specificity and safety and outline the path forward for CAR T therapy beyond cancer.

Dysregulated H19/Igf2 expression disrupts cardiac-placental axis during development of Silver-Russell syndrome-like mouse models

Dysregulation of the imprinted H19/IGF2 locus can lead to Silver-Russell syndrome (SRS) in humans. However, the mechanism of how abnormal H19/IGF2 expression contributes to various SRS phenotypes remains unclear, largely due to incomplete understanding of the developmental functions of these two genes. We previously generated a mouse model with humanized H19/IGF2 imprinting control region (hIC1) on the paternal allele that exhibited H19/Igf2 dysregulation together with SRS-like growth restriction and perinatal lethality. Here, we dissect the role of H19 and Igf2 in cardiac and placental development utilizing multiple mouse models with varying levels of H19 and Igf2. We report severe cardiac defects such as ventricular septal defects and thinned myocardium, placental anomalies including thrombosis and vascular malformations, together with growth restriction in mouse embryos that correlated with the extent of H19/Igf2 dysregulation. Transcriptomic analysis using cardiac endothelial cells of these mouse models shows that H19/Igf2 dysregulation disrupts pathways related to extracellular matrix and proliferation of endothelial cells. Our work links the heart and placenta through regulation by H19 and Igf2, demonstrating that accurate dosage of both H19 and Igf2 is critical for normal embryonic development, especially related to the cardiac-placental axis.

Tissue-specific Grb10/Ddc insulator drives allelic architecture for cardiac development

Allele-specific expression of imprinted gene clusters is governed by gametic DNA methylation at master regulators called imprinting control regions (ICRs). Non-gametic or secondary differentially methylated regions (DMRs) at promoters and exonic regions reinforce monoallelic expression but do not control an entire cluster. Here, we unveil an unconventional secondary DMR that is indispensable for tissue-specific imprinting of two previously unlinked genes, Grb10 and Ddc. Using polymorphic mice, we mapped an intronic secondary DMR at Grb10 with paternal-specific CTCF binding (CBR2.3) that forms contacts with Ddc. Deletion of paternal CBR2.3 removed a critical insulator, resulting in substantial shifting of chromatin looping and ectopic enhancer-promoter contacts. Destabilized gene architecture precipitated abnormal Grb10-Ddc expression with developmental consequences in the heart and muscle. Thus, we redefine the Grb10-Ddc imprinting domain by uncovering an unconventional intronic secondary DMR that functions as an insulator to instruct the tissue-specific, monoallelic expression of multiple genes-a feature previously ICR exclusive.

SARS-CoV-2 disrupts host epigenetic regulation via histone mimicry

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged at the end of 2019 and caused the devastating global pandemic of coronavirus disease 2019 (COVID-19), in part because of its ability to effectively suppress host cell responses1-3. In rare cases, viral proteins dampen antiviral responses by mimicking critical regions of human histone proteins4-8, particularly those containing post-translational modifications required for transcriptional regulation9-11. Recent work has demonstrated that SARS-CoV-2 markedly disrupts host cell epigenetic regulation12-14. However, how SARS-CoV-2 controls the host cell epigenome and whether it uses histone mimicry to do so remain unclear. Here we show that the SARS-CoV-2 protein encoded by ORF8 (ORF8) functions as a histone mimic of the ARKS motifs in histone H3 to disrupt host cell epigenetic regulation. ORF8 is associated with chromatin, disrupts regulation of critical histone post-translational modifications and promotes chromatin compaction. Deletion of either the ORF8 gene or the histone mimic site attenuates the ability of SARS-CoV-2 to disrupt host cell chromatin, affects the transcriptional response to infection and attenuates viral genome copy number. These findings demonstrate a new function of ORF8 and a mechanism through which SARS-CoV-2 disrupts host cell epigenetic regulation. Further, this work provides a molecular basis for the finding that SARS-CoV-2 lacking ORF8 is associated with decreased severity of COVID-19.

Abstract P3096: Cardiac-specific Hadc3 Loss Induces Reorganization Of Peripheral Heterochromatin And Promotes Diet-induced Heart Failure

The nuclear periphery, including the nuclear lamina, serves as an important three-dimensional organizer of the genome. Together, with a subset of tethering proteins, nuclear lamina serves as a platform to anchor transcriptionally silent heterochromatin to the nuclear periphery. Peripheral heterochromatin, marked by the H3K9me2 histone modification, interacts with lamina proteins and is organized into lamina-associated domains (LADs). Our previous studies demonstrated that histone deacetylase 3 (HDAC3) is a scaffold for a nuclear lamina tethering complex and plays an important, non-enzymatic role in establishing cell identity in murine cardiac progenitor cells by reorganizing the LADs and releasing cardiac lineage-specific genes from the nuclear periphery during differentiation. This reorganization is critical as it makes specific genomic regions that are released from the nuclear periphery more accessible for transcriptional activation. Surprisingly, Hdac3 deficiency in murine cardiomyocytes did not lead to any observable phenotype in adult animals. However, when the mice were maintained on a high-fat diet, this resulted in a severe disruption of fat metabolism and lead to heart failure within months. In the present study, we seek to determine if Hdac3 deletion is sufficient to re-organize LADs, release the genes normally found there, and make them more accessible for transcriptional activation as the mechanism leading to cardiac dysfunction. Since H3K9me2 marks peripherally localized genomic regions, we performed H3K9me2 CUT&RUN assay on cardiomyocytes derived from WT and Hdac3 KO mice, fed with normal and high-fat diet, to compare the positioning of chromatin genome-wide. From these data, we identified a list of genes and enhancers found in those regions that vary significantly in H3K9me2 enrichment depending on genotype and condition. We then performed Gene Ontology (GO) Analysis. A significant finding is that numerous enhancers with relatively reduced H3K9me2 in Hdac3 KO cardiomyocytes are regulators of neuronal genes. Loss of H3K9me2 is generally associated with increased gene transcription. We predict that disruption of the peripheral heterochromatin organization upon Hdac3 deletion may result in loss of identity in cardiomyocytes by activating non-cardiomyocyte program-specific genes, such as those of neuronal cell fate, which are normally found at the nuclear periphery and silent in cardiac cells. The results of this work will help to gain insight into the function of nuclear lamina scaffolding proteins, and open new avenues to design therapies to replace lost scaffolding proteins in patients predisposed to heart disease.

β-Hydroxybutyrate suppresses colorectal cancer

Colorectal cancer (CRC) is among the most frequent forms of cancer, and new strategies for its prevention and therapy are urgently needed1. Here we identify a metabolite signalling pathway that provides actionable insights towards this goal. We perform a dietary screen in autochthonous animal models of CRC and find that ketogenic diets exhibit a strong tumour-inhibitory effect. These properties of ketogenic diets are recapitulated by the ketone body β-hydroxybutyrate (BHB), which reduces the proliferation of colonic crypt cells and potently suppresses intestinal tumour growth. We find that BHB acts through the surface receptor Hcar2 and induces the transcriptional regulator Hopx, thereby altering gene expression and inhibiting cell proliferation. Cancer organoid assays and single-cell RNA sequencing of biopsies from patients with CRC provide evidence that elevated BHB levels and active HOPX are associated with reduced intestinal epithelial proliferation in humans. This study thus identifies a BHB-triggered pathway regulating intestinal tumorigenesis and indicates that oral or systemic interventions with a single metabolite may complement current prevention and treatment strategies for CRC.

Uniting Disciplines to Develop Therapeutics: Targeted mRNA Lipid Nanoparticles Reprogram the Immune System In Vivo to Treat Heart Disease

The burgeoning field of immunomedicine is primed to expand beyond oncology (Aghajanian et al., 2022). Over the past several decades, many cell-based therapies have been proposed, developed, and deployed in the clinic. The recent explosion of targeted cell therapies has primarily been aimed at oncological malignancies. In parallel, cardiology researchers have been investigating the various cell types that contribute to heart diseases, especially those responsible for tissue fibrosis and myocardial dysfunction. Our laboratory proposed in 2019 to unite these two disciplines: could a targeted cell therapy be used to ameliorate cardiac fibrosis (Aghajanian et al., 2019). Although preliminary results were encouraging, the genetic engineering approach used to manufacture immune cells would result in persistent cytolytic T cell if directly translated to humans. This would pose a safety concern since activated fibroblasts are essential cells in the setting of acute injury. Therefore, we developed a novel technology to deliver modified RNA to T cells in vivo, resulting in a transient antiactivated fibroblast therapeutic (Rurik et al., 2022). Although active for only a few days, these cells were sufficient to significantly improve cardiac function in a murine model of cardiac fibrosis. These results pave the way for low-cost and scalable, and dose-able and immune therapy for fibrotic disorders.

CAR-based therapies: opportunities for immuno-medicine beyond cancer

One of the most exciting new therapies for cancer involves the use of autologous T cells that are engineered to recognize and destroy cancerous cells. Patients with previously untreatable B cell leukaemias and lymphomas have been cured, and efforts are underway to extend this success to other tumours. Here, we discuss recent studies and emerging research aimed to extend this approach beyond oncology in areas such as cardiometabolic disorders, autoimmunity, fibrosis and senescence. We also summarize new technologies that may help to reduce the cost and increase access to related forms of immunotherapy.

CAR T cells produced in vivo to treat cardiac injury

Fibrosis affects millions of people with cardiac disease. We developed a therapeutic approach to generate transient antifibrotic chimeric antigen receptor (CAR) T cells in vivo by delivering modified messenger RNA (mRNA) in T cell–targeted lipid nanoparticles (LNPs). The efficacy of these in vivo–reprogrammed CAR T cells was evaluated by injecting CD5-targeted LNPs into a mouse model of heart failure. Efficient delivery of modified mRNA encoding the CAR to T lymphocytes was observed, which produced transient, effective CAR T cells in vivo. Antifibrotic CAR T cells exhibited trogocytosis and retained the target antigen as they accumulated in the spleen. Treatment with modified mRNA-targeted LNPs reduced fibrosis and restored cardiac function after injury. In vivo generation of CAR T cells may hold promise as a therapeutic platform to treat various diseases.

CAR T cells produced in vivo to treat cardiac injury

Cardiac fibrosis is the stiffening and scarring of heart tissue and can be fatal. Rurik et al . designed an immunotherapy strategy to generate transient chimeric antigen receptor (CAR) T cells that can recognize the fibrotic cells in the heart (see the Perspective by Gao and Chen). By injecting CD5-targeted lipid nanoparticles containing the messenger RNA (mRNA) instructions needed to reprogram T lymphocytes, the researchers were able to generate therapeutic CAR T cells entirely inside the body. Analysis of a mouse model of heart disease revealed that the approach was successful in reducing fibrosis and restoring cardiac function. The ability to produce CAR T cells in vivo using modified mRNA may have a number of therapeutic applications. —PNK

Landscape of Hopx expression in cells of the immune system

Homeodomain only protein (Hopx) is a regulator of cell differentiation and function, and it has also emerged as a crucial marker of specific developmental and differentiation potentials. Hopx expression and functions have been identified in some stem cells, tumors, and in certain immune cells. However, expression of Hopx in immune cells remains insufficiently characterized. Here we report a comprehensive pattern of Hopx expression in multiple types of immune cells under steady state conditions. By utilizing single-cell RNA sequencing (scRNA-seq) and flow cytometric analysis, we characterize a constitutive expression of Hopx in specific subsets of CD4⁺ and CD8⁺ T cells and B cells, as well as natural killer (NK), NKT, and myeloid cells. In contrast, Hopx expression is not present in conventional dendritic cells and eosinophils. The utility of identifying expression of Hopx in immune cells may prove vital in delineating specific roles of Hopx under multiple immune conditions.

Not all stress is bad for your heart

[Figure: see text].

Global chromatin relabeling accompanies spatial inversion of chromatin in rod photoreceptors

The nuclear architecture of rod photoreceptor cells in nocturnal mammals is unlike that of other animal cells. Murine rod cells have an “inverted” chromatin organization with euchromatin at the nuclear periphery and heterochromatin packed in the center of the nucleus. In conventional nuclear architecture, euchromatin is mostly in the interior, and heterochromatin is largely at the nuclear periphery. We demonstrate that inverted nuclear architecture is achieved through global relabeling of the rod cell epigenome. During rod cell maturation, H3K9me2-labeled nuclear peripheral heterochromatin is relabeled with H3K9me3 and repositioned to the nuclear center, while transcriptionally active euchromatin is labeled with H3K9me2 and positioned at the nuclear periphery. Global chromatin relabeling is correlated with spatial rearrangement, suggesting a critical role for histone modifications, specifically H3K9 methylation, in nuclear architecture. These results reveal a dramatic example of genome-wide epigenetic relabeling of chromatin that accompanies altered nuclear architecture in a postnatal, postmitotic cell.

The nuclear periphery is a scaffold for tissue-specific enhancers

Nuclear architecture influences gene regulation and cell identity by controlling the three-dimensional organization of genes and their distal regulatory sequences, which may be far apart in linear space. The genome is functionally and spatially segregated in the eukaryotic nucleus with transcriptionally active regions in the nuclear interior separated from repressive regions, including those at the nuclear periphery. Here, we describe the identification of a novel type of nuclear peripheral chromatin domain that is enriched for tissue-specific transcriptional enhancers. Like other chromatin at the nuclear periphery, these regions are marked by H3K9me2. But unlike the nuclear peripheral Lamina-Associated Domains (LADs), these novel, enhancer-rich domains have limited Lamin B interaction. We therefore refer to them as H3K9me2-Only Domains (KODs). In mouse embryonic stem cells, KODs are found in Hi-C-defined A compartments and feature relatively accessible chromatin. KODs are characterized by low gene expression and enhancers located in these domains bear the histone marks of an inactive or poised state. These results indicate that KODs organize a subset of inactive, tissue-specific enhancers at the nuclear periphery. We hypothesize that KODs may play a role in facilitating and perhaps constraining the enhancer-promoter interactions underlying spatiotemporal regulation of gene expression programs in differentiation and development.

Immune Cells and Immunotherapy for Cardiac Injury and Repair

Cardiac injury remains a major cause of morbidity and mortality worldwide. Despite significant advances, a full understanding of why the heart fails to fully recover function after acute injury, and why progressive heart failure frequently ensues, remains elusive. No therapeutics, short of heart transplantation, have emerged to reliably halt or reverse the inexorable progression of heart failure in the majority of patients once it has become clinically evident. To date, most pharmacological interventions have focused on modifying hemodynamics (reducing afterload, controlling blood pressure and blood volume) or on modifying cardiac myocyte function. However, important contributions of the immune system to normal cardiac function and the response to injury have recently emerged as exciting areas of investigation. Therapeutic interventions aimed at harnessing the power of immune cells hold promise for new treatment avenues for cardiac disease. Here, we review the immune response to heart injury, its contribution to cardiac fibrosis, and the potential of immune modifying therapies to affect cardiac repair.

SARS-CoV-2 spike protein binding selectively accelerates substrate-specific catalytic activity of ACE2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus that has given rise to the devastating global pandemic. In most cases, SARS-CoV-2 infection results in the development of viral pneumonia and acute respiratory distress syndrome, known as ‘coronavirus disease 2019’ or COVID-19. Intriguingly, besides the respiratory tract, COVID-19 affects other organs and systems of the human body. COVID-19 patients with pre-existing cardiovascular disease have a higher risk of death, and SARS-CoV-2 infection itself may cause myocardial inflammation and injury. One possible explanation of such phenomena is the fact that SARS-CoV-2 utilizes angiotensin-converting enzyme 2 (ACE2) as the receptor required for viral entry. ACE2 is expressed in the cells of many organs, including the heart. ACE2 functions as a carboxypeptidase that can cleave several endogenous substrates, including angiotensin II, thus regulating blood pressure and vascular tone. It remains largely unknown if the SARS-CoV-2 infection alters the enzymatic properties of ACE2, thereby contributing to cardiovascular complications in patients with COVID-19. Here, we demonstrate that ACE2 cleavage of des-Arg9-bradykinin substrate analogue is markedly accelerated, while cleavage of angiotensin II analogue is minimally affected by the binding of spike protein. These findings may have implications for a better understanding of COVID-19 pathogenesis.

Histone methyltransferase activity programs nuclear peripheral genome positioning

Spatial organization of the genome in the nucleus plays a critical role in development and regulation of transcription. A genomic region that resides at the nuclear periphery is part of the chromatin layer marked with histone H3 lysine 9 dimethyl (H3K9me2), but chromatin reorganization during cell differentiation can cause movement in and out of this nuclear compartment with patterns specific for individual cell fates. Here we describe a CRISPR-based system that allows visualization coupled with forced spatial relocalization of a target genomic locus in live cells. We demonstrate that a specified locus can be tethered to the nuclear periphery through direct binding to a dCas9-Lap2β fusion protein at the nuclear membrane, or via targeting of a histone methyltransferase (HMT), G9a fused to dCas9, that promotes H3K9me2 labeling and localization to the nuclear periphery. The enzymatic activity of the HMT is sufficient to promote this repositioning, while disruption of the catalytic activity abolishes the localization effect. We further demonstrate that dCas9-G9a-mediated localization to the nuclear periphery is independent of nuclear actin polymerization. Our data suggest a function for epigenetic histone modifying enzymes in spatial chromatin organization and provide a system for tracking and labeling targeted genomic regions in live cells.

An Engineered Mouse to Identify Proliferating Cells and Their Derivatives

BACKGROUND

Cell proliferation is a fundamental event during development, disease, and regeneration. Effectively tracking and quantifying proliferating cells and their derivatives is critical for addressing many research questions. Cell cycle expression such as for Ki67, proliferating cell nuclear antigen (PCNA), or aurora kinase B (Aurkb), or measurement of 5-bromo-2'-deoxyuridine (BrdU) or 3H-thymidine incorporation have been widely used to assess and quantify cell proliferation. These are powerful tools for detecting actively proliferating cells, but they do not identify cell populations derived from proliferating progenitors over time.

AIMS

We developed a new mouse tool for lineage tracing of proliferating cells by targeting the Aurkb allele.

RESULTS

In quiescent cells or cells arrested at G1/S, little or no Aurkb mRNA is detectable. In cycling cells, Aurkb transcripts are detectable at G2 and become undetectable by telophase. These findings suggest that Aurkb transcription is restricted to proliferating cells and is tightly coupled to cell proliferation. Accordingly, we generated an Aurkb ER Cre/+ mouse by targeting a tamoxifen inducible Cre cassette into the start codon of Aurkb. We find that the Aurkb ER Cre/+ mouse faithfully labels proliferating cells in developing embryos and regenerative adult tissues such as intestine but does not label quiescent cells such as post-mitotic neurons.

CONCLUSION

The Aurkb ER Cre/+ mouse faithfully labels proliferating cells and their derivatives in developing embryos and regenerative adult tissues. This new mouse tool provides a novel genetic tracing capability for studying tissue proliferation and regeneration.

Author Correction: Targeting cardiac fibrosis with engineered T cells

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

H3K9me2 orchestrates inheritance of spatial positioning of peripheral heterochromatin through mitosis

Cell-type-specific 3D organization of the genome is unrecognizable during mitosis. It remains unclear how essential positional information is transmitted through cell division such that a daughter cell recapitulates the spatial genome organization of the parent. Lamina-associated domains (LADs) are regions of repressive heterochromatin positioned at the nuclear periphery that vary by cell type and contribute to cell-specific gene expression and identity. Here we show that histone 3 lysine 9 dimethylation (H3K9me2) is an evolutionarily conserved, specific mark of nuclear peripheral heterochromatin and that it is retained through mitosis. During mitosis, phosphorylation of histone 3 serine 10 temporarily shields the H3K9me2 mark allowing for dissociation of chromatin from the nuclear lamina. Using high-resolution 3D immuno-oligoFISH, we demonstrate that H3K9me2-enriched genomic regions, which are positioned at the nuclear lamina in interphase cells prior to mitosis, re-associate with the forming nuclear lamina before mitotic exit. The H3K9me2 modification of peripheral heterochromatin ensures that positional information is safeguarded through cell division such that individual LADs are re-established at the nuclear periphery in daughter nuclei. Thus, H3K9me2 acts as a 3D architectural mitotic guidepost. Our data establish a mechanism for epigenetic memory and inheritance of spatial organization of the genome.

Semaphorin 3E/PlexinD1 signaling is required for cardiac ventricular compaction

Left ventricular noncompaction (LVNC) is one of the most common forms of genetic cardiomyopathy characterized by excessive trabeculation and impaired myocardial compaction during fetal development. Patients with LVNC are at higher risk of developing left/right ventricular failure or both. Although the key regulators for cardiac chamber development are well studied, the role of semaphorin (Sema)/plexin signaling in this process remains poorly understood. In this article, we demonstrate that genetic deletion of Plxnd1, a class-3 Sema receptor in endothelial cells, leads to severe cardiac chamber defects. They were characterized by excessive trabeculation and noncompaction similar to patients with LVNC. Loss of Plxnd1 results in decreased expression of extracellular matrix proteolytic genes, leading to excessive deposition of cardiac jelly. We demonstrate that Plxnd1 deficiency is associated with an increase in Notch1 expression and its downstream target genes. In addition, inhibition of the Notch signaling pathway partially rescues the excessive trabeculation and noncompaction phenotype present in Plxnd1 mutants. Furthermore, we demonstrate that Semaphorin 3E (Sema3E), one of PlexinD1's known ligands, is expressed in the developing heart and is required for myocardial compaction. Collectively, our study uncovers what we believe to be a previously undescribed role of the Sema3E/PlexinD1 signaling pathway in myocardial trabeculation and the compaction process.

Abstract 633: Semaphorin3e-Plexind1 Signaling is Required for Cardiac Ventricular Compaction

Left ventricular noncompaction (LVNC) is one of the most common forms of genetic cardiomyopathy characterized by excessive trabeculation and impaired myocardial compaction during fetal development. LVNC patients are at higher risk to develop left or right ventricular failure, or both. While key regulators for cardiac chamber development are well studied, the role of Semaphorin-Plexin signaling in this process remains poorly understood. Here, we demonstrate that genetic deletion of Plxnd1, a class 3 semaphorin receptor in endothelial cells, leads to severe cardiac chamber defects, as characterized by excessive trabeculation and non-compaction similar to LVNC patients. Loss of Plxnd1 results in decreased expression of extracellular matrix (ECM) proteolytic genes leading to excessive deposition of cardiac jelly. We demonstrate that Plxnd1 deficiency is associated with an increase in the expression of Notch and its downstream target genes. In addition, inhibition of Notch signaling pathway can partially rescue the excessive trabeculation and non-compaction phenotype present in Plxnd1 mutants. Furthermore, we demonstrate that Semaphorin 3e (Sema3e), one of Plxnd1’s ligands is expressed in the developing heart and is required for myocardial compaction. Collectively, our results demonstrate that the Sema3e-Plxnd1 pathway is essential for myocardial trabeculation and compaction.

A Common Embryonic Origin of Stem Cells Drives Developmental and Adult Neurogenesis

New neurons arise from quiescent adult neural progenitors throughout life in specific regions of the mammalian brain. Little is known about the embryonic origin and establishment of adult neural progenitors. Here, we show that Hopx+ precursors in the mouse dentate neuroepithelium at embryonic day 11.5 give rise to proliferative Hopx+ neural progenitors in the primitive dentate region, and they, in turn, generate granule neurons, but not other neurons, throughout development and then transition into Hopx+ quiescent radial glial-like neural progenitors during an early postnatal period. RNA-seq and ATAC-seq analyses of Hopx+ embryonic, early postnatal, and adult dentate neural progenitors further reveal common molecular and epigenetic signatures and developmental dynamics. Together, our findings support a "continuous" model wherein a common neural progenitor population exclusively contributes to dentate neurogenesis throughout development and adulthood. Adult dentate neurogenesis may therefore represent a lifelong extension of development that maintains heightened plasticity in the mammalian hippocampus.

Lineage-specific reorganization of nuclear peripheral heterochromatin and H3K9me2 domains

Dynamic organization of chromatin within the three-dimensional nuclear space has been postulated to regulate gene expression and cell fate. Here, we define the genome-wide distribution of nuclear peripheral heterochromatin as a multipotent P19 cell adopts either a neural or a cardiac fate. We demonstrate that H3K9me2-marked nuclear peripheral heterochromatin undergoes lineage-specific reorganization during cell-fate determination. This is associated with spatial repositioning of genomic loci away from the nuclear periphery as shown by 3D immuno-FISH. Locus repositioning is not always associated with transcriptional changes, but a subset of genes is upregulated. Mef2c is specifically repositioned away from the nuclear periphery during early neurogenic differentiation, but not during early cardiogenic differentiation, with associated transcript upregulation. Myocd is specifically repositioned during early cardiogenic differentiation, but not during early neurogenic differentiation, and is transcriptionally upregulated at later stages of cardiac differentiation. We provide experimental evidence for lineage-specific regulation of nuclear architecture during cell-fate determination in a mouse cell line.

Competent for commitment: you've got to have heart!

This review by Jain and Epstein discusses the developmental processes that influence cardiac lineage decisions and cellular competence and advances our understanding of cardiac cell specification, gene regulation, and chromatin organization and how they impact cardiac development.

The mature heart is composed primarily of four different cell types: cardiac myocytes, endothelium, smooth muscle, and fibroblasts. These cell types derive from pluripotent progenitors that become progressively restricted with regard to lineage potential, giving rise to multipotent cardiac progenitor cells and, ultimately, the differentiated cell types of the heart. Recent studies have begun to shed light on the defining characteristics of the intermediary cell types that exist transiently during this developmental process and the extrinsic and cell-autonomous factors that influence cardiac lineage decisions and cellular competence. This information will shape our understanding of congenital and adult cardiac disease and guide regenerative therapeutic approaches. In addition, cardiac progenitor specification can serve as a model for understanding basic mechanisms regulating the acquisition of cellular identity. In this review, we present the concept of “chromatin competence” that describes the potential for three-dimensional chromatin organization to function as the molecular underpinning of the ability of a progenitor cell to respond to inductive lineage cues and summarize recent studies advancing our understanding of cardiac cell specification, gene regulation, and chromatin organization and how they impact cardiac development.

Beating the odds: programming proliferation in the mammalian heart

The heart is one of the least regenerative organs in the human body; adult cardiac myocytes divide at extremely low frequency. Therefore, meaningful induction of cardiac regeneration requires in-depth understanding of myocyte cell-cycle control. Recent insights into how myocytes can be coaxed into duplicating in vivo might inform emerging therapeutics.

Endocardial Hippo signaling regulates myocardial growth and cardiogenesis

The Hippo signaling pathway has been implicated in control of cell and organ size, proliferation, and endothelial-mesenchymal transformation. This pathway impacts upon two partially redundant transcription cofactors, Yap and Taz, that interact with other factors, including members of the Tead family, to affect expression of downstream genes. Yap and Taz have been shown to regulate, in a cell-autonomous manner, myocardial proliferation, myocardial hypertrophy, regenerative potential, and overall size of the heart. Here, we show that Yap and Taz also play an instructive, non-cell-autonomous role in the endocardium of the developing heart to regulate myocardial growth through release of the paracrine factor, neuregulin. Without endocardial Yap and Taz, myocardial growth is impaired causing early post-natal lethality. Thus, the Hippo signaling pathway regulates cell size via both cell-autonomous and non-cell-autonomous mechanisms. Furthermore, these data suggest that Hippo may regulate organ size via a sensing and paracrine function in endothelial cells.

Zinc transporter Slc39a8 is essential for cardiac ventricular compaction

Isolated left ventricular noncompaction (LVNC) results from excessive trabeculation and impaired myocardial compaction during heart development. The extracellular matrix (ECM) that separates endocardium from myocardium plays a critical but poorly understood role in ventricular trabeculation and compaction. In an attempt to characterize solute carrier family 39 member 8-null (Slc39a8-null) mice, we discovered that homozygous null embryos do not survive embryogenesis and exhibit a cardiac phenotype similar to human LVNC. Slc39a8 encodes a divalent metal cation importer that has been implicated in ECM degradation through the zinc/metal regulatory transcription factor 1 (Zn/MTF1) axis, which promotes the expression of ECM-degrading enzymes, including Adamts metalloproteinases. Here, we have shown that Slc39a8 is expressed by endothelial cells in the developing mouse heart, where it serves to maintain cellular Zn levels. Furthermore, Slc39a8-null hearts exhibited marked ECM accumulation and reduction of several Adamts metalloproteinases. Consistent with the in vivo observations, knockdown of SLC39A8 in HUVECs decreased ADAMTS1 transcription by decreasing cellular Zn uptake and, as a result, MTF1 transcriptional activity. Our study thus identifies a gene underlying ventricular trabeculation and compaction development, and a pathway regulating ECM during myocardial morphogenesis.

Genome-Nuclear Lamina Interactions Regulate Cardiac Stem Cell Lineage Restriction

Progenitor cells differentiate into specialized cell types through coordinated expression of lineage-specific genes and modification of complex chromatin configurations. We demonstrate that a histone deacetylase (Hdac3) organizes heterochromatin at the nuclear lamina during cardiac progenitor lineage restriction. Specification of cardiomyocytes is associated with reorganization of peripheral heterochromatin, and independent of deacetylase activity, Hdac3 tethers peripheral heterochromatin containing lineage-relevant genes to the nuclear lamina. Deletion of Hdac3 in cardiac progenitor cells releases genomic regions from the nuclear periphery, leading to precocious cardiac gene expression and differentiation into cardiomyocytes; in contrast, restricting Hdac3 to the nuclear periphery rescues myogenesis in progenitors otherwise lacking Hdac3. Our results suggest that availability of genomic regions for activation by lineage-specific factors is regulated in part through dynamic chromatin-nuclear lamina interactions and that competence of a progenitor cell to respond to differentiation signals may depend upon coordinated movement of responding gene loci away from the nuclear periphery.

ProteinProcessor: A probabilistic analysis using mass accuracy and the MS spectrum

Current approaches to protein identification rely heavily on database matching of fragmentation spectra or precursor peptide ions. We have developed a method for MALDI TOF-TOF instrumentation that uses peptide masses and their measurement errors to confirm protein identifications from a first pass MS/MS database search. The method uses MS1-level spectral data that have heretofore been ignored by most search engines. This approach uses the distribution of mass errors of peptide matches in the MS1 spectrum to develop a probability model that is independent of the MS/MS database search identifications. Peptide mass matches can come from both precursor ions that have been fragmented as well as those that are tentatively identified by accurate mass alone. This additional corroboration enables us to confirm protein identifications to MS/MS-based scores that are otherwise considered to be only of moderate quality. Straightforward and easily applicable to current proteomic analyses, this tool termed "ProteinProcessor" provides a robust and invaluable addition to current protein identification tools.

A radial axis defined by semaphorin-to-neuropilin signaling controls pancreatic islet morphogenesis

The islets of Langerhans are endocrine organs characteristically dispersed throughout the pancreas. During development, endocrine progenitors delaminate, migrate radially and cluster to form islets. Despite the distinctive distribution of islets, spatially localized signals that control islet morphogenesis have not been discovered. Here, we identify a radial signaling axis that instructs developing islet cells to disperse throughout the pancreas. A screen of pancreatic extracellular signals identified factors that stimulated islet cell development. These included semaphorin 3a, a guidance cue in neural development without known functions in the pancreas. In the fetal pancreas, peripheral mesenchymal cells expressed Sema3a, while central nascent islet cells produced the semaphorin receptor neuropilin 2 (Nrp2). Nrp2 mutant islet cells developed in proper numbers, but had defects in migration and were unresponsive to purified Sema3a. Mutant Nrp2 islets aggregated centrally and failed to disperse radially. Thus, Sema3a-Nrp2 signaling along an unrecognized pancreatic developmental axis constitutes a chemoattractant system essential for generating the hallmark morphogenetic properties of pancreatic islets. Unexpectedly, Sema3a- and Nrp2-mediated control of islet morphogenesis is strikingly homologous to mechanisms that regulate radial neuronal migration and cortical lamination in the developing mammalian brain.

Epicardial YAP/TAZ orchestrate an immunosuppressive response following myocardial infarction

Ischemic heart disease resulting from myocardial infarction (MI) is the most prevalent form of heart disease in the United States. Post-MI cardiac remodeling is a multifaceted process that includes activation of fibroblasts and a complex immune response. T-regulatory cells (Tregs), a subset of CD4+ T cells, have been shown to suppress the innate and adaptive immune response and limit deleterious remodeling following myocardial injury. However, the mechanisms by which injured myocardium recruits suppressive immune cells remain largely unknown. Here, we have shown a role for Hippo signaling in the epicardium in suppressing the post-infarct inflammatory response through recruitment of Tregs. Mice deficient in epicardial YAP and TAZ, two core Hippo pathway effectors, developed profound post-MI pericardial inflammation and myocardial fibrosis, resulting in cardiomyopathy and death. Mutant mice exhibited fewer suppressive Tregs in the injured myocardium and decreased expression of the gene encoding IFN-γ, a known Treg inducer. Furthermore, controlled local delivery of IFN-γ following MI rescued Treg infiltration into the injured myocardium of YAP/TAZ mutants and decreased fibrosis. Collectively, these results suggest that epicardial Hippo signaling plays a key role in adaptive immune regulation during the post-MI recovery phase.

Mapping the Pairwise Choices Leading from Pluripotency to Human Bone, Heart, and Other Mesoderm Cell Types

Stem-cell differentiation to desired lineages requires navigating alternating developmental paths that often lead to unwanted cell types. Hence, comprehensive developmental roadmaps are crucial to channel stem-cell differentiation toward desired fates. To this end, here, we map bifurcating lineage choices leading from pluripotency to 12 human mesodermal lineages, including bone, muscle, and heart. We defined the extrinsic signals controlling each binary lineage decision, enabling us to logically block differentiation toward unwanted fates and rapidly steer pluripotent stem cells toward 80%-99% pure human mesodermal lineages at most branchpoints. This strategy enabled the generation of human bone and heart progenitors that could engraft in respective in vivo models. Mapping stepwise chromatin and single-cell gene expression changes in mesoderm development uncovered somite segmentation, a previously unobservable human embryonic event transiently marked by HOPX expression. Collectively, this roadmap enables navigation of mesodermal development to produce transplantable human tissue progenitors and uncover developmental processes. VIDEO ABSTRACT.

A Perspective on the Value of Aquatic Models in Biomedical Research

For at least 150 years, biological scientists have congregated at marine laboratories, located at the edge of the sea, to explore aquatic life. The purpose of this minireview is to offer a brief perspective on the relevance of this activity to our knowledge of human physiology and disease, drawing heavily on the experience of the authors and without attempting to offer a comprehensive history of the many contributions of marine models to biomedical research.

Abstract 2456: Synergy between loss of NF1 and overexpression of MYCN in neuroblastoma is mediated by the GAP-related domain

Earlier reports indicated that the role of Nf1 tumor suppressor gene in limiting sympathoadrenal cell growth during embryologic development is independent of its ability to down-modulate RAS-MAPK signaling. This finding raised the question of whether neuroblastoma pathogenesis was also accelerated by loss of a similar non-canonical function of NF1. To elucidate how loss of the NF1 tumor suppressor gene contributes to the development of high-risk neuroblastoma, we relied on a transgenic zebrafish model that overexpresses MYCN and harbors loss-of-function nf1 mutations. We show here that loss of nf1 leads to aberrant activation of RAS signaling in MYCN-induced neuroblastoma, promoting both increased tumor cell survival and rapid tumor cell proliferation. We demonstrate further that the GTPase-activating protein (GAP) activity of the (GAP)-related domain (GRD) is sufficient to suppress accelerated initiation of neuroblastoma in nf1-deficient zebrafish, even though this transgene is unable to restrict abnormal sympathoadrenal cell growth during embryologic development. Hence NF1 exhibits different activities in vivo in the normal development and tumorigenesis of the peripheral sympathetic nervous system. Our findings establish nf1-deficient zebrafish that overexpress MYCN as an ideal animal model system for investigating new strategies to improve treatment of very high risk neuroblastomas with aberrant RAS-MAPK activation. We are currently performing high-throughput in vivo drug analysis using these zebrafish with primary tumors.

Citation Format: Shuning He, Marc R. Mansour, Mark W. Zimmerman, Dong Hyuk Ki, Hillary M. Layden, Koshi Akahane, Eric D. de Groh, Antonio R. Perez-Atayde, Shizhen Zhu, Jonathan A. Epstein, A Thomas Look. Synergy between loss of NF1 and overexpression of MYCN in neuroblastoma is mediated by the GAP-related domain. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2456.

Coronary vasculature patterning requires a novel endothelial ErbB2 holoreceptor

Organogenesis and regeneration require coordination of cellular proliferation, regulated in part by secreted growth factors and cognate receptors, with tissue nutrient supply provided by expansion and patterning of blood vessels. Here we reveal unexpected combinatorial integration of a growth factor co-receptor with a heterodimeric partner and ligand known to regulate angiogenesis and vascular patterning. We show that ErbB2, which can mediate epidermal growth factor (EGF) and neuregulin signalling in multiple tissues, is unexpectedly expressed by endothelial cells where it partners with neuropilin 1 (Nrp1) to form a functional receptor for the vascular guidance molecule semaphorin 3d (Sema3d). Loss of Sema3d leads to improper patterning of the coronary veins, a phenotype recapitulated by endothelial loss of ErbB2. These findings have implications for possible cardiovascular side-effects of anti-ErbB2 therapies commonly used for cancer, and provide an example of integration at the molecular level of pathways involved in tissue growth and vascular patterning.

Semaphorin ligands and cognate receptors are important in patterning the vasculature. Here, Aghajanian et al. report an unexpected role for ErbB2 in endothelial cells where it partners with Nrp1 to form a novel semaphoring holoreceptor required for embryonic vascular patterning.

Synergy between loss of NF1 and overexpression of MYCN in neuroblastoma is mediated by the GAP-related domain

Earlier reports showed that hyperplasia of sympathoadrenal cell precursors during embryogenesis in Nf1-deficient mice is independent of Nf1’s role in down-modulating RAS-MAPK signaling. We demonstrate in zebrafish that nf1 loss leads to aberrant activation of RAS signaling in MYCN-induced neuroblastomas that arise in these precursors, and that the GTPase-activating protein (GAP)-related domain (GRD) is sufficient to suppress the acceleration of neuroblastoma in nf1-deficient fish, but not the hypertrophy of sympathoadrenal cells in nf1 mutant embryos. Thus, even though neuroblastoma is a classical “developmental tumor”, NF1 relies on a very different mechanism to suppress malignant transformation than it does to modulate normal neural crest cell growth. We also show marked synergy in tumor cell killing between MEK inhibitors (trametinib) and retinoids (isotretinoin) in primary nf1a-/- zebrafish neuroblastomas. Thus, our model system has considerable translational potential for investigating new strategies to improve the treatment of very high-risk neuroblastomas with aberrant RAS-MAPK activation.

DOI:http://dx.doi.org/10.7554/eLife.14713.001

Neuroblastoma is one of the most common childhood cancers and is responsible for about 15% of childhood deaths due to cancer. The neuroblastoma tumors arise in cells that develop into and form part of the body’s nervous system. Many researchers have studied the genetics of this disease and have recognised common patterns. In particular, neuroblastomas can occur when a protein called MYCN is over-produced and a tumor suppressor protein called NF1 is lost.

NF1 is a large protein with several distinct parts or domains. The most studied domain of NF1 is called the GRD, and it is mainly responsible for dampening down signals that cause cells to grow, specialize and survive. However, experiments in mice have revealed that this protein uses its other domains to control the normal development of part of the nervous system.

He et al. wanted to know which domains of NF1 are important for suppressing the growth of neuroblastomas. The experiments were conducted in zebrafish that had been engineered to produce an excess of the human version of MYCN. When He et al. also deleted the gene for the zebrafish’s version of NF1, the fish quickly developed neuroblastomas. Supplying the zebrafish with just the GRD of NF1 was enough to supress the growth of the tumors. These experiments show that NF1 uses different domains and signalling pathways to regulate the normal development of part of the nervous system and to prevent formation of neuroblastoma.

These engineered zebrafish represent an animal model of neuroblastoma that mimics the human disease in many ways. This model will make it possible to test new drug combinations and to find more effective treatments for neuroblastoma patients.

DOI:http://dx.doi.org/10.7554/eLife.14713.002

Loss of neurofibromin Ras-GAP activity enhances the formation of cardiac blood islands in murine embryos

Type I neurofibromatosis (NF1) is caused by mutations in the NF1 gene encoding neurofibromin. Neurofibromin exhibits Ras GTPase activating protein (Ras-GAP) activity that is thought to mediate cellular functions relevant to disease phenotypes. Loss of murine Nf1 results in embryonic lethality due to heart defects, while mice with monoallelic loss of function mutations or with tissue-specific inactivation have been used to model NF1. Here, we characterize previously unappreciated phenotypes in Nf1^-/- embryos, which are inhibition of hemogenic endothelial specification in the dorsal aorta, enhanced yolk sac hematopoiesis, and exuberant cardiac blood island formation. We show that a missense mutation engineered into the active site of the Ras-GAP domain is sufficient to reproduce ectopic blood island formation, cardiac defects, and overgrowth of neural crest-derived structures seen in Nf1^-/-embryos. These findings demonstrate a role for Ras-GAP activity in suppressing the hemogenic potential of the heart and restricting growth of neural crest-derived tissues.

DOI:http://dx.doi.org/10.7554/eLife.07780.001

Messages are carried from the surface of a cell to the cell’s nucleus in order to regulate various processes such as how often the cell will divide. The Ras-signaling pathway carries some of these messages. A gene called Nf1 encodes a protein in this pathway that deactivates another protein called Ras when the message is no longer required. If a mutation in Nf1 prevents it from deactivating Ras, the pathway becomes hyperactivated. In humans, this results in a disorder called Neurofibromatosis type I, which is characterized by tumors that affect many parts of the body.

When the expression of Nf1 is turned off in mice, the mice die as embryos because of cardiac defects. But a mouse in which Nf1 has been turned off in specific organs or tissues other than the heart can survive, and these mice are used to model Neurofibromatosis type I and to help to identify potential treatments.

Yzaguirre et al. have now identified new roles for Nf1 during embryonic development. In the embryo, blood cells originate from the cells lining the blood vessels. The experiments revealed that, when the Nf1 gene was mutated in mice, fewer blood cells formed from the lining of the major blood vessel that leaves the embryonic heart. In contrast, these mutant mice formed more structures called cardiac blood islands than a normal mouse. These structures line the heart, and have the potential to generate new blood cells for the heart to pump. These results shed new light on how blood is originally formed from the lining of the heart and blood vessels, and show that Ras signaling must be tightly regulated to maintain normal blood development in the embryo.

Furthermore, Yzaguirre et al. demonstrated that this excessive formation of cardiac blood islands resulted specifically from the loss of Nf1’s role in the Ras-signaling pathway. This was achieved by using gene targeting to generate a mouse that expresses Nf1 with a minor change that affects only the protein’s interaction with Ras. In the future, this new strain of mouse will be a useful tool in determining if specific aspects of Neurofibromatosis type I can be attributed to loss of Nf1’s role in Ras-signaling and could therefore be treated by medicines that target this pathway.

DOI:http://dx.doi.org/10.7554/eLife.07780.002

Hopx distinguishes hippocampal from lateral ventricle neural stem cells

In the adult dentate gyrus (DG) and in the proliferative zone lining the lateral ventricle (LV-PZ), radial glia-like (RGL) cells are neural stem cells (NSCs) that generate granule neurons. A number of molecular markers including glial fibrillary acidic protein (GFAP), Sox2 and nestin, can identify quiescent NSCs in these two niches. However, to date, there is no marker that distinguishes NSC origin of DG versus LV-PZ. Hopx, an atypical homeodomain only protein, is expressed by adult stem cell populations including those in the intestine and hair follicle. Here, we show that Hopx is specifically expressed in RGL cells in the adult DG, and these cells give rise to granule neurons. Assessed by non-stereological quantitation, Hopx-null NSCs exhibit enhanced neurogenesis evident by an increased number of BrdU-positive cells and doublecortin (DCX)-positive neuroblasts. In contrast, Sox2-positive, quiescent NSCs are reduced in the DG of Hopx-null animals and Notch signaling is reduced, as evidenced by reduced expression of Notch targets Hes1 and Hey2, and a reduction of the number of cells expressing the cleaved, activated form of the Notch1 receptor, the Notch intracellular domain (NICD) in Hopx-null DG. Surprisingly, Hopx is not expressed in RGL cells of the adult LV-PZ, and Hopx-expressing cells do not give rise to interneurons of the olfactory bulb (OB). These findings establish that Hopx expression distinguishes NSCs of the DG from those of the LV-PZ, and suggest that Hopx potentially regulates hippocampal neurogenesis by modulating Notch signaling.

Hippo signaling is required for Notch-dependent smooth muscle differentiation of neural crest

Notch signaling has well-defined roles in the assembly of arterial walls and in the development of the endothelium and smooth muscle of the vasculature. Hippo signaling regulates cellular growth in many tissues, and contributes to regulation of organ size, in addition to other functions. Here, we show that the Notch and Hippo pathways converge to regulate smooth muscle differentiation of the neural crest, which is crucial for normal development of the aortic arch arteries and cranial vasculature during embryonic development. Neural crest-specific deletion of the Hippo effectors Yap and Taz produces neural crest precursors that migrate normally, but fail to produce vascular smooth muscle, and Notch target genes such as Jagged1 fail to activate normally. We show that Yap is normally recruited to a tissue-specific Jagged1 enhancer by directly interacting with the Notch intracellular domain (NICD). The Yap-NICD complex is recruited to chromatin by the DNA-binding protein Rbp-J in a Tead-independent fashion. Thus, Hippo signaling can modulate Notch signaling outputs, and components of the Hippo and Notch pathways physically interact. Convergence of Hippo and Notch pathways by the mechanisms described here might be relevant for the function of these signaling cascades in many tissues and in diseases such as cancer.

Phosphodiesterase sequence variants may predispose to prostate cancer

We hypothesized that mutations that inactivate phosphodiesterase (PDE) activity and lead to increased cAMP and cyclic guanosine monophosphate levels may be associated with prostate cancer (PCa). We sequenced the entire PDE coding sequences in the DNA of 16 biopsy samples from PCa patients. Novel mutations were confirmed in the somatic or germline state by Sanger sequencing. Data were then compared to the 1000 Genome Project. PDE, CREB and pCREB protein expression was also studied in all samples, in both normal and abnormal tissue, by immunofluorescence. We identified three previously described PDE sequence variants that were significantly more frequent in PCa. Four novel sequence variations, one each in the PDE4B,PDE6C, PDE7B and PDE10A genes, respectively, were also found in the PCa samples. Interestingly, PDE10A and PDE4B novel variants that were present in 19 and 6% of the patients were found in the tumor tissue only. In patients carrying PDE defects, there was pCREB accumulation (P<0.001), and an increase of the pCREB:CREB ratio (patients 0.97±0.03; controls 0.52±0.03; P-value <0.001) by immunohistochemical analysis. We conclude that PDE sequence variants may play a role in the predisposition and/or progression to PCa at the germline and/or somatic state respectively.

HEART DEVELOPMENT. Integration of Bmp and Wnt signaling by Hopx specifies commitment of cardiomyoblasts

Cardiac progenitor cells are multipotent and give rise to cardiac endothelium, smooth muscle, and cardiomyocytes. Here, we define and characterize the cardiomyoblast intermediate that is committed to the cardiomyocyte fate, and we characterize the niche signals that regulate commitment. Cardiomyoblasts express Hopx, which functions to coordinate local Bmp signals to inhibit the Wnt pathway, thus promoting cardiomyogenesis. Hopx integrates Bmp and Wnt signaling by physically interacting with activated Smads and repressing Wnt genes. The identification of the committed cardiomyoblast that retains proliferative potential will inform cardiac regenerative therapeutics. In addition, Bmp signals characterize adult stem cell niches in other tissues where Hopx-mediated inhibition of Wnt is likely to contribute to stem cell quiescence and to explain the role of Hopx as a tumor suppressor.