Are crash causation studies the best way to understand system failures - Who can we blame?

The search for common and serious single causes of road crashes naturally leads to a concentration on the road user. This is supported by a legal framework in the search for the main cause and the suspect for this cause. In prevention, we havefor decades been more inclined to look for systematic improvements of all elements of the road transport system, and we direct the recommendations for actions towards system designers, organizations, products and services. In this paper the discussion about causation and prevention is broadened in the light of Vision Zero and its approach to prevention of serious and fatal injuries. We also discuss the Swedish judicial system and why the prevention approach has not been legislated or even generally accepted. Occupational health and safety legislation and road rules are compared, as well as how sustainability practices and reporting are tools to apply prevention where organizations have a natural sphere of influence that could mitigate deaths and serious injuries within value chains. It is recommended that we stop using the term causation as it is only directing actions in one direction. There is a risk that the focus on causation, in particular single causes, will deviate actions away from robust prevention countermeasures such as increased seat belt use, relevant speed limits, and well functioning roundabouts and median barriers. Furthermore, there is also a risk that important preventative actions from organizations are overlooked.

SGOL1-AS1 enhances cell survival in acute myeloid leukemia by maintaining pro-inflammatory signaling.

Epigenetic dysregulation is a key feature of most acute myeloid leukemia (AML). Recently, it has become clear that long noncoding RNAs (lncRNAs) can play a key role in epigenetic regulation, and consequently also dysregulation. Currently, our understanding of the requirements and roles of lncRNAs in AML is still limited. Here, using CRISPRi screening, we identified the lncRNA SGOL1-AS1 as an essential regulator of survival in THP-1 AML cells. We demonstrated that SGOL1-AS1 interacts with chromatin-modifying proteins involved in gene repression and that SGOL1-AS1 knockdown is associated with increased heterochromatin formation. We also observed that loss of SGOLl-AS1 results in increased apoptosis and the downregulation of pro-inflammatory genes. In AML patients, high expression of SGOL1-AS1 correlates with both pro-inflammatory gene expression and poor survival. Altogether, our data reveal that SGOL1-AS1 is an essential regulator of cell survival in AML cell lines and a possible regulator of pro-inflammatory signaling in AML patients.

Murine AGM single-cell profiling identifies a continuum of hemogenic endothelium differentiation marked by ACE.

In vitro generation and expansion of hematopoietic stem cells (HSCs) holds great promise for the treatment of any ailment that relies on bone marrow or blood transplantation. To achieve this, it is essential to resolve the molecular and cellular pathways that govern HSC formation in the embryo. HSCs first emerge in the aorta-gonad-mesonephros (AGM) region, where a rare subset of endothelial cells, hemogenic endothelium (HE), undergoes an endothelial-to-hematopoietic transition (EHT). Here, we present full-length single-cell RNA sequencing (scRNA-seq) of the EHT process with a focus on HE and dorsal aorta niche cells. By using Runx1b and Gfi1/1b transgenic reporter mouse models to isolate HE, we uncovered that the pre-HE to HE continuum is specifically marked by angiotensin-I converting enzyme (ACE) expression. We established that HE cells begin to enter the cell cycle near the time of EHT initiation when their morphology still resembles endothelial cells. We further demonstrated that RUNX1 AGM niche cells consist of vascular smooth muscle cells and PDGFRa+ mesenchymal cells and can functionally support hematopoiesis. Overall, our study provides new insights into HE differentiation toward HSC and the role of AGM RUNX1+ niche cells in this process. Our expansive scRNA-seq datasets represents a powerful resource to investigate these processes further.

Enhancer recruitment of transcription repressors RUNX1 and TLE3 by mis-expressed FOXC1 blocks differentiation in acute myeloid leukemia.

Despite absent expression in normal hematopoiesis, the Forkhead factor FOXC1, a critical mesenchymal differentiation regulator, is highly expressed in ∼30% of HOXAhigh acute myeloid leukemia (AML) cases to confer blocked monocyte/macrophage differentiation. Through integrated proteomics and bioinformatics, we find that FOXC1 and RUNX1 interact through Forkhead and Runt domains, respectively, and co-occupy primed and active enhancers distributed close to differentiation genes. FOXC1 stabilizes association of RUNX1, HDAC1, and Groucho repressor TLE3 to limit enhancer activity: FOXC1 knockdown induces loss of repressor proteins, gain of CEBPA binding, enhancer acetylation, and upregulation of nearby genes, including KLF2. Furthermore, it triggers genome-wide redistribution of RUNX1, TLE3, and HDAC1 from enhancers to promoters, leading to repression of self-renewal genes, including MYC and MYB. Our studies highlight RUNX1 and CEBPA transcription factor swapping as a feature of leukemia cell differentiation and reveal that FOXC1 prevents this by stabilizing enhancer binding of a RUNX1/HDAC1/TLE3 transcription repressor complex to oncogenic effect.

Reduction of RUNX1 transcription factor activity by a CBFA2T3-mimicking peptide: application to B cell precursor acute lymphoblastic leukemia.

BACKGROUND: B Cell Precursor Acute Lymphoblastic Leukemia (BCP-ALL) is the most common pediatric cancer. Identifying key players involved in proliferation of BCP-ALL cells is crucial to propose new therapeutic targets. Runt Related Transcription Factor 1 (RUNX1) and Core-Binding Factor Runt Domain Alpha Subunit 2 Translocated To 3 (CBFA2T3, ETO2, MTG16) are master regulators of hematopoiesis and are implicated in leukemia. METHODS: We worked with BCP-ALL mononuclear bone marrow patients' cells and BCP-ALL cell lines, and performed Chromatin Immunoprecipitations followed by Sequencing (ChIP-Seq), co-immunoprecipitations (co-IP), proximity ligation assays (PLA), luciferase reporter assays and mouse xenograft models. RESULTS: We demonstrated that CBFA2T3 transcript levels correlate with RUNX1 expression in the pediatric t(12;21) ETV6-RUNX1 BCP-ALL. By ChIP-Seq in BCP-ALL patients' cells and cell lines, we found that RUNX1 is recruited on its promoter and on an enhancer of CBFA2T3 located - 2 kb upstream CBFA2T3 promoter and that, subsequently, the transcription factor RUNX1 drives both RUNX1 and CBFA2T3 expression. We demonstrated that, mechanistically, RUNX1 and CBFA2T3 can be part of the same complex allowing CBFA2T3 to strongly potentiate the activity of the transcription factor RUNX1. Finally, we characterized a CBFA2T3-mimicking peptide that inhibits the interaction between RUNX1 and CBFA2T3, abrogating the activity of this transcription complex and reducing BCP-ALL lymphoblast proliferation. CONCLUSIONS: Altogether, our findings reveal a novel and important activation loop between the transcription regulator CBFA2T3 and the transcription factor RUNX1 that promotes BCP-ALL proliferation, supporting the development of an innovative therapeutic approach based on the NHR2 subdomain of CBFA2T3 protein.

Contributions of Embryonic HSC-Independent Hematopoiesis to Organogenesis and the Adult Hematopoietic System.

During ontogeny, the establishment of the hematopoietic system takes place in several phases, separated both in time and location. The process is initiated extra-embryonically in the yolk sac (YS) and concludes in the main arteries of the embryo with the formation of hematopoietic stem cells (HSC). Initially, it was thought that HSC-independent hematopoietic YS cells were transient, and only required to bridge the gap to HSC activity. However, in recent years it has become clear that these cells also contribute to embryonic organogenesis, including the emergence of HSCs. Furthermore, some of these early HSC-independent YS cells persist into adulthood as distinct hematopoietic populations. These previously unrecognized abilities of embryonic HSC-independent hematopoietic cells constitute a new field of interest. Here, we aim to provide a succinct overview of the current knowledge regarding the contribution of YS-derived hematopoietic cells to the development of the embryo and the adult hematopoietic system.

CUL2LRR1 , TRAIP and p97 control CMG helicase disassembly in the mammalian cell cycle.

The eukaryotic replisome is disassembled in each cell cycle, dependent upon ubiquitylation of the CMG helicase. Studies of Saccharomyces cerevisiae, Caenorhabditis elegans and Xenopus laevis have revealed surprising evolutionary diversity in the ubiquitin ligases that control CMG ubiquitylation, but regulated disassembly of the mammalian replisome has yet to be explored. Here, we describe a model system for studying the ubiquitylation and chromatin extraction of the mammalian CMG replisome, based on mouse embryonic stem cells. We show that the ubiquitin ligase CUL2LRR1 is required for ubiquitylation of the CMG-MCM7 subunit during S-phase, leading to disassembly by the p97 ATPase. Moreover, a second pathway of CMG disassembly is activated during mitosis, dependent upon the TRAIP ubiquitin ligase that is mutated in primordial dwarfism and mis-regulated in various cancers. These findings indicate that replisome disassembly in diverse metazoa is regulated by a conserved pair of ubiquitin ligases, distinct from those present in other eukaryotes.

The RUNX1b Isoform Defines Hemogenic Competency in Developing Human Endothelial Cells.

The transcription factor RUNX1 is a master regulator of blood cell specification. During embryogenesis, hematopoietic progenitors are initially generated from hemogenic endothelium through an endothelium-to-hematopoietic transition controlled by RUNX1. Several studies have dissected the expression pattern and role of RUNX1 isoforms at the onset of mouse hematopoiesis, however the precise pattern of RUNX1 isoform expression and biological output of RUNX1-expressing cells at the onset of human hematopoiesis is still not fully understood. Here, we investigated these questions using a RUNX1b:VENUS RUNX1c:TOMATO human embryonic stem cell line which allows multi-parameter single cell resolution via flow cytometry and isolation of RUNX1b-expressing cells for further analysis. Our data reveal the sequential expression of the two RUNX1 isoforms with RUNX1b expressed first in a subset of endothelial cells and during the endothelial to hematopoietic transition while RUNX1c only becomes expressed in fully specified blood cells. Furthermore, our data show that RUNX1b marks endothelial cells endowed with hemogenic potential and that RUNX1b expression level determines hemogenic competency in a dose-dependent manner. Together our data reveal the dynamic of RUNX1 isoforms expression at the onset of human blood specification and establish RUNX1b isoform as the earliest known marker for hemogenic competency.

RUNX1 Dosage in Development and Cancer.

The transcription factor RUNX1 first came to prominence due to its involvement in the t(8;21) translocation in acute myeloid leukemia (AML). Since this discovery, RUNX1 has been shown to play important roles not only in leukemia but also in the ontogeny of the normal hematopoietic system. Although it is currently still challenging to fully assess the different parameters regulating RUNX1 dosage, it has become clear that the dose of RUNX1 can greatly affect both leukemia and normal hematopoietic development. It is also becoming evident that varying levels of RUNX1 expression can be used as markers of tumor progression not only in the hematopoietic system, but also in non-hematopoietic cancers. Here, we provide an overview of the current knowledge of the effects of RUNX1 dosage in normal development of both hematopoietic and epithelial tissues and their associated cancers.

Identification of gene specific cis-regulatory elements during differentiation of mouse embryonic stem cells: An integrative approach using high-throughput datasets.

Gene expression governs cell fate, and is regulated via a complex interplay of transcription factors and molecules that change chromatin structure. Advances in sequencing-based assays have enabled investigation of these processes genome-wide, leading to large datasets that combine information on the dynamics of gene expression, transcription factor binding and chromatin structure as cells differentiate. While numerous studies focus on the effects of these features on broader gene regulation, less work has been done on the mechanisms of gene-specific transcriptional control. In this study, we have focussed on the latter by integrating gene expression data for the in vitro differentiation of murine ES cells to macrophages and cardiomyocytes, with dynamic data on chromatin structure, epigenetics and transcription factor binding. Combining a novel strategy to identify communities of related control elements with a penalized regression approach, we developed individual models to identify the potential control elements predictive of the expression of each gene. Our models were compared to an existing method and evaluated using the existing literature and new experimental data from embryonic stem cell differentiation reporter assays. Our method is able to identify transcriptional control elements in a gene specific manner that reflect known regulatory relationships and to generate useful hypotheses for further testing.

RUNX transcription factors: orchestrators of development.

RUNX transcription factors orchestrate many different aspects of biology, including basic cellular and developmental processes, stem cell biology and tumorigenesis. In this Primer, we introduce the molecular hallmarks of the three mammalian RUNX genes, RUNX1, RUNX2 and RUNX3, and discuss the regulation of their activities and their mechanisms of action. We then review their crucial roles in the specification and maintenance of a wide array of tissues during embryonic development and adult homeostasis.

Multifocal Primary Prostate Cancer Exhibits High Degree of Genomic Heterogeneity.

BACKGROUND: Most primary prostate cancers are multifocal with individual tumors harboring different aggressiveness; however, the genomic heterogeneity among these tumors is poorly understood. OBJECTIVE: To better understand the biological basis for clinical variability among different lesions, we sought to comprehensively characterize the heterogeneity of somatic gene mutations in multifocal prostate cancer. DESIGN, SETTING, AND PARTICIPANTS: High-coverage whole-exome sequencing of 153 frozen tissue samples, taken from two to three distinct tumor foci and one non-cancerous area from each of 41 patients, covering a total of 89 tumor foci. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: State-of-the-art bioinformatics tools for mutation calling and copy number determination from whole-exome sequencing data. RESULTS AND LIMITATIONS: We found a very high degree of interfocal heterogeneity among tumors, that is, 76% of pairwise-compared tumor foci from the same prostatectomy specimen had no point mutations in common and DNA copy number changes were rarely shared across cancer foci. The few point mutations shared across tumor foci were seldom in cancer-critical genes. CONCLUSIONS: In this first large genomic heterogeneity study of primary prostate cancer, we observe that different tumor foci within the same patient are genetically distinct, only rarely sharing any somatic gene mutations, including those in cancer driver genes. This heterogeneity affects how genomics-based management of prostate cancer can be implemented, as information from all tumor foci is necessary to draw valid conclusions about the cancer's genomic alterations. PATIENT SUMMARY: Most primary prostate cancers consist of multiple tumors within the same organ, but little is known about their relationships. We have compared the sets of gene mutations among such tumors and found that they only exceptionally have any in common. This will influence treatment decisions in the future as each tumor's mutations will render it unique and have to be considered to gain the best treatment results.

Combined MR Imaging of Oxygen Consumption and Supply Reveals Tumor Hypoxia and Aggressiveness in Prostate Cancer Patients.

The established role of hypoxia-induced signaling in prostate cancer growth, metastasis, and response to treatment suggests that a method to image hypoxia in tumors could aid treatment decisions. Here, we present consumption and supply-based hypoxia (CSH) imaging, an approach that integrates images related to oxygen consumption and supply into a single image. This integration algorithm was developed in patients with prostate cancer receiving hypoxia marker pimonidazole prior to prostatectomy. We exploited the intravoxel incoherent motion (IVIM) signal in diagnostic diffusion-weighted (DW) magnetic resonance (MR) images to generate separate images of the apparent diffusion coefficient (ADC) and fractional blood volume (fBV). ADC and fBV correlated with cell density (CD) and blood vessel density (BVD) in histology and whole-mount sections from 35 patients, thus linking ADC to oxygen consumption and fBV to oxygen supply. Pixel-wise plots of ADC versus fBV were utilized to predict the hypoxia status of each pixel in a tumor and to visualize the predicted value in a single image. The hypoxic fraction (HFDWI) of CSH images correlated strongly (R2 = 0.66; n = 41) with pimonidazole immunoscore (HSPimo); this relationship was validated in a second pimonidazole cohort (R2 = 0.54; n = 54). We observed good agreement between CSH images and pimonidazole staining in whole-mount sections. HFDWI correlated with tumor stage and lymph node status, consistent with findings for HSPimo Moreover, CSH imaging could be applied on histologic CD and BVD images, demonstrating transferability to a histopathology assay. Thus, CSH represents a robust approach for hypoxia imaging in prostate cancer that could easily be translated into clinical practice.Significance: These findings present a novel imaging strategy that indirectly measures tumor hypoxia and has potential application in a wide variety of solid tumors and other imaging modalities.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/16/4774/F1.large.jpg Cancer Res; 78(16); 4774-85. ©2018 AACR.

Regulation of RUNX1 dosage is crucial for efficient blood formation from hemogenic endothelium.

During ontogeny, hematopoietic stem and progenitor cells arise from hemogenic endothelium through an endothelial-to-hematopoietic transition that is strictly dependent on the transcription factor RUNX1. Although it is well established that RUNX1 is essential for the onset of hematopoiesis, little is known about the role of RUNX1 dosage specifically in hemogenic endothelium and during the endothelial-to-hematopoietic transition. Here, we used the mouse embryonic stem cell differentiation system to determine if and how RUNX1 dosage affects hemogenic endothelium differentiation. The use of inducible Runx1 expression combined with alterations in the expression of the RUNX1 co-factor CBFß allowed us to evaluate a wide range of RUNX1 levels. We demonstrate that low RUNX1 levels are sufficient and necessary to initiate an effective endothelial-to-hematopoietic transition. Subsequently, RUNX1 is also required to complete the endothelial-to-hematopoietic transition and to generate functional hematopoietic precursors. In contrast, elevated levels of RUNX1 are able to drive an accelerated endothelial-to-hematopoietic transition, but the resulting cells are unable to generate mature hematopoietic cells. Together, our results suggest that RUNX1 dosage plays a pivotal role in hemogenic endothelium maturation and the establishment of the hematopoietic system.

Safety and acceptability of human papillomavirus testing of self-collected specimens: A methodologic study of the impact of collection devices and HPV assays on sensitivity for cervical cancer and high-grade lesions.

BACKGROUND: Comparative data on different self-collection methods is limited. OBJECTIVES: To assess the impact of hrHPV testing of two self-collection devices for detection of cervical carcinoma and high-grade lesions. STUDY DESIGN: Three hundred ten patients collected two cervicovaginal specimens using a brush (Evalyn®Brush) and a swab (FLOQSwabs™), and filled a questionnaire at home. Then, a physician at the clinic took a cervical specimen into PreservCyt® buffer for hrHPV testing and cytology. All specimens were tested using Anyplex™ II HPV28, Cobas® 4800 HPV Test and Xpert®HPV. RESULTS: Performance comparison included 45 cervical carcinomas and 187 patients with premalignant lesions. Compared to the physician-specimen, hrHPV testing of Evalyn®Brush showed non-inferior sensitivity for CIN3+ (relative sensitivity of Anyplex™ 0.99; Cobas® 0.96; Xpert®HPV 0.97) while hrHPV testing of FLOQSwabs™ showed inferior sensitivity (relative sensitivity of Anyplex™ 0.91; Cobas® 0.92; Xpert®HPV 0.93). Similar results were observed for invasive carcinomas albeit that FLOQSwabs™ was statistically non-inferior to the physician-specimen. Self-collection by either Evalyn®Brush or FLOQSwabs™ was more sensitive for CIN3+ than LSIL or worse cytology. Significant decrease in sensitivity for CIN3+ were observed for FLOQSwabs™ when specimens were preprocessed for hrHPV testing after 28 days. Both devices were well accepted, but patients considered Evalyn®Brush easier and more comfortable than FLOQSwabs™. CONCLUSIONS: Self-collection is comparable to current screening practice for detecting cervical carcinoma and CIN3+ but device and specimen processing effects exist. Only validated procedure including collection device, hrHPV assay and specimen preparation should be used.

Trends in incidence, mortality and survival of penile squamous cell carcinoma in Norway 1956-2015.

We examine trends in incidence, mortality and survival of penile squamous cell carcinoma (SCC) in Norway over 60 years. Data on all cases of penile cancer diagnosed in Norway during 1956-2015 were obtained from the Cancer Registry of Norway. Trends in age-standardized rates of penile SCC incidence, mortality and 5-year relative survival were assessed by the annual percentage change statistic and joinpoint regression. A total of 1,596 penile cancer cases were diagnosed during 1956-2015, among which 1,474 (92.4%) were SCC. During 2011-2015, the age-standardized incidence and mortality of penile SCC were 0.91 (95% confidence interval (CI): 0.78; 1.05) and 0.50 (0.42; 0.60) per 100,000, respectively, and the 5-year relative survival was 61.6% (41.9; 76.4). The incidence of SCC increased during 1956-2015, with an average annual percentage change (AAPC) of 0.80% (0.46; 1.15). The increase was strongest among men diagnosed at a relatively early age (age<=64 years; AAPC: 1.47% (0.90; 2.05)). Mortality also increased over the study period (AAPC: 0.47% (0.10; 0.85)), whereas 5-year relative survival did not change (AAPC: 0.08% (-0.19; 0.36)). We conclude that the incidence of penile SCC has increased at a moderate and constant rate during 1956-2015, and that the most consistent increase occurred among younger men. Mortality also increased during the study period. However, survival did not change, thus changes in diagnostics and treatment had little impact on survival from penile SCC. Since a substantial proportion of penile SCC is caused by human papillomavirus (HPV), the incidence increase may in part be attributed to increased exposure to HPV in the population.

HPV genotype profile in a Norwegian cohort with ASC-US and LSIL cytology with three year cumulative risk of high grade cervical neoplasia.

OBJECTIVE: To explore the HPVgenotype profile in Norwegian women with ASC-US/LSIL cytology and the subsequent risk of high-grade cervical neoplasia (CIN 3+). METHODS: In this observational study delayed triage of ASC-US/LSIL of 6058 women were included from 2005 to 2010. High-risk HPV detection with Hybrid Capture 2 (HC2) was used and the HC2+ cases were genotyped with in-house nmPCR. Women were followed-up for histologically confirmed CIN3+ within three years of index HPV test by linkage to the screening databases at the Cancer Registry of Norway. RESULTS: HC2 was positive in 45% (2756/6058) of the women. Within 3years CIN3+ was diagnosed in 26% of women<34year and in 15%≥34year. HC2 was positive at index in 94% of CIN3+ cases and negative in 64 cases including three women with cervical carcinomas. Women<34years with single infections of HPV 16, 35, 58 or 33 or multiple infections including HPV 16, 52, 33 or 31 were associated with highest proportions of CIN 3+. Older women with single infection with HPV 16, 33, 31 or 35 or multiple infections including HPV 16, 33, 31 or 18/39 were more likely to develop CIN 3+. CONCLUSIONS: HPV 16 and HPV 33 at baseline both as single or multiple infections, were associated with the highest risk for CIN3+. Among older women, all 13 high-risk genotypes as single infection were associated with >20% risk of CIN3+. Further studies are necessary to risk stratify the individual genotypes to reduce the number of colposcopies in Norway.

Pharmacokinetics of S-ketamine during prolonged sedation at the pediatric intensive care unit.

BACKGROUND: S-ketamine is the S(+)-enantiomer of the racemic mixture ketamine, an anesthetic drug providing both sedation and analgesia. In clinical practice, significant interpatient variability in drug effect of S-ketamine is observed during long-term sedation. AIMS: The aim of this study was to evaluate the pharmacokinetic variability of S-ketamine in children aged 0-18 years during long-term sedation. Twenty-five children (median age: 0.42 years, range: 0.02-12.5) received continuous intravenous administrations of 0.3-3.6 mg/kg/h S-ketamine for sedation during mechanical ventilation. Infusion rates were adjusted to the desired level of sedation and analgesia based on the COMFORT-B score and Visual Analog Scale. Blood samples were drawn once daily at random time-points, and at 1 and 4 hours after discontinuation of S-ketamine infusion. Time profiles of plasma concentrations of S-ketamine and active metabolite S-norketamine were analyzed using nonlinear mixed-effects modeling software. Clearance and volume of distribution were allometrically scaled using the ¾ power model. RESULTS: A total of 86 blood samples were collected. A 2-compartment and 1-compartment model adequately described the PK of S-ketamine and S-norketamine, respectively. The typical parameter estimates for clearance and central and peripheral volumes of distribution were: CLS-KETAMINE =112 L/h/70 kg, V1S-KETAMINE =7.7 L/70 kg, V2S-KETAMINE =545L/70 kg, QS-kETAMINE =196 L/h/70 kg, and CLS-NORKETAMINE =53 L/h/70 kg. Interpatient variability of CLS-KETAMINE and CLS-NORKETAMINE was considerable with values of 40% and 104%, respectively, leading to marked variability in steady-state plasma concentrations. CONCLUSION: Substantial interpatient variability in pharmacokinetics in children complicates the development of adequate dosage regimen for continuous sedation.

Cooperative binding of AP-1 and TEAD4 modulates the balance between vascular smooth muscle and hemogenic cell fate.

The transmission of extracellular signals into the nucleus involves inducible transcription factors, but how different signalling pathways act in a cell type-specific fashion is poorly understood. Here, we studied the regulatory role of the AP-1 transcription factor family in blood development using embryonic stem cell differentiation coupled with genome-wide transcription factor binding and gene expression analyses. AP-1 factors respond to MAP kinase signalling and comprise dimers of FOS, ATF and JUN proteins. To examine genes regulated by AP-1 and to examine how it interacts with other inducible transcription factors, we abrogated its global DNA-binding activity using a dominant-negative FOS peptide. We show that FOS and JUN bind to and activate a specific set of vascular genes and that AP-1 inhibition shifts the balance between smooth muscle and hematopoietic differentiation towards blood. Furthermore, AP-1 is required for de novo binding of TEAD4, a transcription factor connected to Hippo signalling. Our bottom-up approach demonstrates that AP-1- and TEAD4-associated cis-regulatory elements form hubs for multiple signalling-responsive transcription factors and define the cistrome that regulates vascular and hematopoietic development by extrinsic signals.

Interplay between SOX7 and RUNX1 regulates hemogenic endothelial fate in the yolk sac.

Endothelial to hematopoietic transition (EHT) is a dynamic process involving the shutting down of endothelial gene expression and switching on of hematopoietic gene transcription. Although the factors regulating EHT in hemogenic endothelium (HE) of the dorsal aorta have been relatively well studied, the molecular regulation of yolk sac HE remains poorly understood. Here, we show that SOX7 inhibits the expression of RUNX1 target genes in HE, while having no effect on RUNX1 expression itself. We establish that SOX7 directly interacts with RUNX1 and inhibits its transcriptional activity. Through this interaction we demonstrate that SOX7 hinders RUNX1 DNA binding as well as the interaction between RUNX1 and its co-factor CBFß. Finally, we show by single-cell expression profiling and immunofluorescence that SOX7 is broadly expressed across the RUNX1+ yolk sac HE population compared with SOX17. Collectively, these data demonstrate for the first time how direct protein-protein interactions between endothelial and hematopoietic transcription factors regulate contrasting transcriptional programs during HE differentiation and EHT.