Direct observation of a condensate effect on super-enhancer controlled gene bursting.

Enhancers are distal DNA elements believed to loop and contact promoters to control gene expression. Recently, we found diffraction-sized transcriptional condensates at genes controlled by clusters of enhancers (super-enhancers). However, a direct function of endogenous condensates in controlling gene expression remains elusive. Here, we develop live-cell super-resolution and multi-color 3D-imaging approaches to investigate putative roles of endogenous condensates in the regulation of super-enhancer controlled gene Sox2. In contrast to enhancer distance, we find instead that the condensate's positional dynamics are a better predictor of gene expression. A basal gene bursting occurs when the condensate is far (>1 µm), but burst size and frequency are enhanced when the condensate moves in proximity (<1 µm). Perturbations of cohesin and local DNA elements do not prevent basal bursting but affect the condensate and its burst enhancement. We propose a three-way kissing model whereby the condensate interacts transiently with gene locus and regulatory DNA elements to control gene bursting.

RNA-Mediated Feedback Control of Transcriptional Condensates.

Regulation of biological processes typically incorporates mechanisms that initiate and terminate the process and, where understood, these mechanisms often involve feedback control. Regulation of transcription is a fundamental cellular process where the mechanisms involved in initiation have been studied extensively, but those involved in arresting the process are poorly understood. Modeling of the potential roles of RNA in transcriptional control suggested a non-equilibrium feedback control mechanism where low levels of RNA promote condensates formed by electrostatic interactions whereas relatively high levels promote dissolution of these condensates. Evidence from in vitro and in vivo experiments support a model where RNAs produced during early steps in transcription initiation stimulate condensate formation, whereas the burst of RNAs produced during elongation stimulate condensate dissolution. We propose that transcriptional regulation incorporates a feedback mechanism whereby transcribed RNAs initially stimulate but then ultimately arrest the process.

Regularly spaced tyrosines in EBF1 mediate BRG1 recruitment and formation of nuclear subdiffractive clusters.

B lineage priming by pioneer transcription factor EBF1 requires the function of an intrinsically disordered region (IDR). Here, we examine the role of regularly spaced tyrosines in the IDR as potential determinants of IDR function and activity of EBF1. We found that four Y > A mutations in EBF1 reduced the formation of condensates in vitro and subdiffractive clusters in vivo. Notably, Y > A mutant EBF1 was inefficient in promoting B cell differentiation and showed impaired chromatin binding, recruitment of BRG1, and activation of specific target genes. Thus, regularly spaced tyrosines in the IDR contribute to the biophysical and functional properties of EBF1.

Mediator Condensates Localize Signaling Factors to Key Cell Identity Genes.

The gene expression programs that define the identity of each cell are controlled by master transcription factors (TFs) that bind cell-type-specific enhancers, as well as signaling factors, which bring extracellular stimuli to these enhancers. Recent studies have revealed that master TFs form phase-separated condensates with the Mediator coactivator at super-enhancers. Here, we present evidence that signaling factors for the WNT, TGF-ß, and JAK/STAT pathways use their intrinsically disordered regions (IDRs) to enter and concentrate in Mediator condensates at super-enhancers. We show that the WNT coactivator ß-catenin interacts both with components of condensates and DNA-binding factors to selectively occupy super-enhancer-associated genes. We propose that the cell-type specificity of the response to signaling is mediated in part by the IDRs of the signaling factors, which cause these factors to partition into condensates established by the master TFs and Mediator at genes with prominent roles in cell identity.

Pol II phosphorylation regulates a switch between transcriptional and splicing condensates.

The synthesis of pre-mRNA by RNA polymerase II (Pol II) involves the formation of a transcription initiation complex, and a transition to an elongation complex1-4. The large subunit of Pol II contains an intrinsically disordered C-terminal domain that is phosphorylated by cyclin-dependent kinases during the transition from initiation to elongation, thus influencing the interaction of the C-terminal domain with different components of the initiation or the RNA-splicing apparatus5,6. Recent observations suggest that this model provides only a partial picture of the effects of phosphorylation of the C-terminal domain7-12. Both the transcription-initiation machinery and the splicing machinery can form phase-separated condensates that contain large numbers of component molecules: hundreds of molecules of Pol II and mediator are concentrated in condensates at super-enhancers7,8, and large numbers of splicing factors are concentrated in nuclear speckles, some of which occur at highly active transcription sites9-12. Here we investigate whether the phosphorylation of the Pol II C-terminal domain regulates the incorporation of Pol II into phase-separated condensates that are associated with transcription initiation and splicing. We find that the hypophosphorylated C-terminal domain of Pol II is incorporated into mediator condensates and that phosphorylation by regulatory cyclin-dependent kinases reduces this incorporation. We also find that the hyperphosphorylated C-terminal domain is preferentially incorporated into condensates that are formed by splicing factors. These results suggest that phosphorylation of the Pol II C-terminal domain drives an exchange from condensates that are involved in transcription initiation to those that are involved in RNA processing, and implicates phosphorylation as a mechanism that regulates condensate preference.

High frequency of antimicrobial resistance in Salmonella and Escherichia coli causing diarrheal diseases at the Yirimadio community health facility, Mali.

BACKGROUND: Diarrhoea is a public health problem, especially in developing countries where it is the second leading cause of child mortality. In Low Income Countries like in Mali, self-medication and inappropriate use of antibiotics due to the scarcity of complementary diagnostic systems can lead to the development of multidrug-resistant bacteria causing diarrhoea. The objective of this work was to determine the microorganisms responsible for diarrhoea in children under 15 years of age and to characterize their sensitivity to a panel of antibiotics used in a peri-urban community in Mali. The study involved outpatient children visiting the Yirimadio Community Health Centre and diagnosed with diarrhoea. Stool samples from those patients were collected and analysed by conventional stools culture and the susceptibility to antibiotics of detected bacteria was determined by the disc diffusion method in an agar medium. RESULT: Overall, 554 patients were included. Children under the age of 3 years accounted for 88.8% (492 of 554) of our study population. Two bacterial species were isolated in this study, Escherichia coli 31.8% (176 of 554) and Salmonella 2.9% (16 of 554). In the 176, E. coli strains resistance to amoxicillin and to cotrimoxazole was seen in 93.8% (165 of 176) and 92.6% ( 163 of 176), respectively. The ESBL resistance phenotype accounted for 39,8% (70 of 176) of E. coli. Sixteen (16) strains of Salmonella were found, of which one strain (6.3%) was resistant to amoxicillin and to amoxicillin + clavulanic acid. Another one was resistant to chloramphenicol (6.3%). Two strains of Salmonella were resistant to cotrimoxazole (12.5%) and two others were resistant to cefoxitin (12.5%). CONCLUSIONS: The data suggest that E. coli is frequently involved in diarrhoea in children under 3 years of age in this peri-urban setting of Bamako, Mali, with a high rate of resistance to amoxicillin and cotrimoxazole, the most widely used antibiotics in the management of diarrhoea in this setting.

Epidemiological profile of occupational risks associated with artisanal burning of plastic materials in Parakou / Profil épidémiologique des risques professionnels associés au brûlage artisanal de matières plastiques à Parakou

Introduction: Burning plastic releases toxic fumes and gases. More and more people engage in the professional activity of welding plastic parts by fusion in Benin. Hence the need for this study. Purpose of research: To assess the frequency of the various occupational risks associated with the welding of plastic materials by burning in Parakou. A cross-sectional, descriptive, and analytical study focused on plastic welders in Parakou. The data was collected using a questionnaire. The variables studied were accidents at work, occupational diseases, and socio-professional characteristics. The data was analyzed by Epi info version 7.2.1.0. The significance level was set at p < 0.05. Results: A total of 137 subjects were surveyed. They were all male. Almost all of them were victims of accidents at work. The lesions were mainly on the fingers (99%) and feet (99%). The most expressed morbid manifestations were musculoskeletal disorders (98%), rhinitis (87%), cough (79%), tearing (98%) and conjunctival hyperemia (93%). Conclusions: Plastic welding in Parakou is a high health risk activity for craftsmen. It is urgent to take protective measures for these craftsmen.

Introduction: La combustion du plastique dégage des fumées et des gaz toxiques. De plus en plus de personnes se livrent à l'activité professionnelle de soudage de pièces en plastique par fusion au Bénin, d'où la nécessité de cette étude. But de l'étude: Évaluer la fréquence des différents risques professionnels associés au soudage de matières plastiques par brûlage à Parakou. Il s'agit d'une étude transversale, descriptive et à visée analytique qui a porté sur les soudeurs de plastiques à Parakou. Les données ont été collectées à l'aide d'un questionnaire. Les variables étudiées étaient l'accident du travail, les maladies professionnelles et les caractéristiques socioprofessionnelles. Les données ont été analysées par Épi info version 7.2.1.0. Le seuil de signification a été fixé à p < 0,05. Résultats: Au total 137 sujets ont été enquêtés. Ils étaient tous de sexe masculin. La quasi-totalité d'entre eux était victime d'accidents du travail. Les lésions siégeaient surtout aux doigts (99 %) et aux pieds (99 %). Les manifestations morbides les plus exprimées étaient les troubles musculo-squelettiques (98 %), la rhinite (87 %), la toux (79 %), le larmoiement (98 %) et l'hyperhémie conjonctivale (94 %). Conclusions: Le soudage de plastique à Parakou est une activité à risque sanitaire élevé pour les artisans. La prise de mesures protectrices pour ces artisans est urgente.

Applying WHO COVID-19 workforce estimate tools remotely in an African context: a case report from Mali and Kenya.

BACKGROUND: The COVID-19 pandemic has increased the burden on health systems, particularly in low- and middle-income countries, where health systems already struggle. To meet health workforce planning needs during the pandemic, IntraHealth International used two tools created by the World Health Organization (WHO) Regional Office for Europe. The Health Workforce Estimator (HWFE) allows the estimation of the quantity of health workers needed to treat patients during a surge, and the Adaptt Surge Planning Support Tool helps to predict the timing of a surge in cases and the number of health workers and beds needed for predicted caseload. These tools were adapted to fit the African context in a rapid implementation over 5 weeks in one region in Mali and one region in Kenya with the objective to test the feasibility of adapting these tools, which use a Workload Indicators of Staffing Need (WISN)-inspired human resources management methodology, to obtain daily and surge projections of COVID-19 human resources for health needs. CASE PRESENTATION: Using a remote team in the US and in-country teams in Mali and Kenya, IntraHealth enacted a phased plan to gather stakeholder support, collect data related to health systems and COVID-19 cases, populate data into the tools, verify modeled results with results on the ground, enact policy measures to meet projected needs, and conduct national training workshops for the ministries of health. CONCLUSIONS: This phased implementation in Mali and Kenya demonstrated that the WISN approach applied to the Health Workforce Estimator and Adaptt tools can be readily adapted to the local context for African countries to rapidly estimate the number of health workers and beds needed to respond to the predicted COVID-19 pandemic caseload. The results may also be used to give a proxy estimate for needed health supplies-e.g., oxygen, medications, and ventilators. Challenges included accurate and timely data collection and updating data. The success of the pilot can be attributed to the adapted WHO tools, the team composition in both countries, access to human resources data, and early support of the ministries of health, with the expectation that this methodology can be applied to other country contexts.

Risk of obstructive sleep apnea among taxi-motorbike drivers in Parakou city in West Africa and associated factors with road traffic accidents.

OBJECTIVES: Obstructive sleep apnea (OSA) is an underdiagnosed chronic respiratory disease, causing excessive daytime sleepiness (EDS) and road traffic accidents (RTA). This study aimed to determine the risk of OSA among taxi-motorbike drivers (TMD) and factors associated with RTA in Parakou, Benin. METHODS: A cross-sectional comparative study was carried out between July and September 2020, including 225 TMD and 450 motorbike drivers other than TMD (non-TMD). A multiple logistic regression was then performed to determine factors associated with RTA. RESULTS: The mean age of participants was 38.2 ± 10.2 and 36.6 ±10.9 years, respectively, for TMD and non-TMD (p = .048). The average daily working time was 10.7 ± 2.3H and 9.1±3.5H, respectively, for TMD and non-TMD (p < .001). Average sleeping time was comparable in both groups (7.5±1.4H vs 7.4±1.4H; p = .415). TMD significantly more complained of non-restorative sleep (38.7% vs 18.4%; p < .001) but less of EDS (20.0% vs 28.7%; p = .015). Abdominal obesity predominated in TMD (13.8% vs 4.4%; p < .001). An increased risk of OSA (NoSAS score ≥8) was diagnosed in 25.8% TMD and 26.7% non-TMD (p = .805). Overall, 25.8% of TMD and 18.4% of non-TMD (p = .027) reported at least one RTA in the last 12 months. After adjusted analysis, the unique factor associated with RTA was a daily sleeping pills consumption (aOR=2.2; 95%CI = 1.2-3.8; p = .006). CONCLUSION: There is need to improve systematic screening and diagnosis of OSA in both TMD and non-TMD and reinforce the regulation and consumption of sleeping pills.

Hsp70-Bag3 complex is a hub for proteotoxicity-induced signaling that controls protein aggregation.

Protein abnormalities in cells are the cause of major pathologies, and a number of adaptive responses have evolved to relieve the toxicity of misfolded polypeptides. To trigger these responses, cells must detect the buildup of aberrant proteins which often associate with proteasome failure, but the sensing mechanism is poorly understood. Here we demonstrate that this mechanism involves the heat shock protein 70-Bcl-2-associated athanogene 3 (Hsp70-Bag3) complex, which upon proteasome suppression responds to the accumulation of defective ribosomal products, preferentially recognizing the stalled polypeptides. Components of the ribosome quality control system LTN1 and VCP and the ribosome-associated chaperone NAC are necessary for the interaction of these species with the Hsp70-Bag3 complex. This complex regulates important signaling pathways, including the Hippo pathway effectors LATS1/2 and the p38 and JNK stress kinases. Furthermore, under proteotoxic stress Hsp70-Bag3-LATS1/2 signaling regulates protein aggregation. We established that the regulated step was the emergence and growth of abnormal protein oligomers containing only a few molecules, indicating that aggregation is regulated at very early stages. The Hsp70-Bag3 complex therefore functions as an important signaling node that senses proteotoxicity and triggers multiple pathways that control cell physiology, including activation of protein aggregation.

A CRISPR/Cas9 platform for MS2-labelling of single mRNA in live stem cells.

The MS2 system is a powerful tool for investigating transcription dynamics at the single molecule directly in live cells. In the past, insertion of the RNA-labelling cassette at specific gene loci has been a major hurdle. Here, we present a CRISPR/Cas9-based approach to insert an MS2 cassette with selectable marker at the start of the 3' untranslated region of any coding gene. We demonstrate applicability of our approach by tagging RNA of the stem cell transcription factor Esrrb in mouse embryonic stem cells. Using quantitative fluorescence microscopy we determine the number of nascent transcripts at the Esrrb locus and the fraction of cells expressing the gene. We find that upon differentiation towards epiblast-like cells, expression of Esrrb is down-regulated in an increasing fraction of cells in a binary manner.

Global analysis of double-strand break processing reveals in vivo properties of the helicase-nuclease complex AddAB.

In bacteria, double-strand break (DSB) repair via homologous recombination is thought to be initiated through the bi-directional degradation and resection of DNA ends by a helicase-nuclease complex such as AddAB. The activity of AddAB has been well-studied in vitro, with translocation speeds between 400-2000 bp/s on linear DNA suggesting that a large section of DNA around a break site is processed for repair. However, the translocation rate and activity of AddAB in vivo is not known, and how AddAB is regulated to prevent excessive DNA degradation around a break site is unclear. To examine the functions and mechanistic regulation of AddAB inside bacterial cells, we developed a next-generation sequencing-based approach to assay DNA processing after a site-specific DSB was introduced on the chromosome of Caulobacter crescentus. Using this assay we determined the in vivo rates of DSB processing by AddAB and found that putative chi sites attenuate processing in a RecA-dependent manner. This RecA-mediated regulation of AddAB prevents the excessive loss of DNA around a break site, limiting the effects of DSB processing on transcription. In sum, our results, taken together with prior studies, support a mechanism for regulating AddAB that couples two key events of DSB repair-the attenuation of DNA-end processing and the initiation of homology search by RecA-thereby helping to ensure that genomic integrity is maintained during DSB repair.

Work environment and hypertension in industrial settings in Benin in 2019: a cross-sectional study.

OBJECTIVE: To determine the association between occupational factors, particularly psychosocial factors, and hypertension. DESIGN: Descriptive and analytical cross-sectional study using logistic multivariate regression. SETTING: Fifteen cotton ginning plants in Benin. PARTICIPANTS: Permanent and occasional workers in the cotton ginning industry. DATA COLLECTION: Data on sociodemographic, occupational, behavioural and clinical history characteristics were collected using a number of standardised, interviewer-administered questionnaires. These questionnaires were based on the WHO's non-communicable disease questionnaire, Karasek questionnaire and Siegrist questionnaire. Weight, height and blood pressure were measured. Any worker with systolic blood pressure ≥140 mm Hg and/or diastolic blood pressure ≥90 mm Hg according to the WHO criteria was considered hypertensive, as was any subject on antihypertensive treatment even if blood pressure was normal. RESULTS: A total of 1883 workers were included, with a male to female ratio of 9.08. Of these, 510 suffered from hypertension (27.1%, 95% CI 25.1 to 29.2). In the multivariate analysis, the risk factors identified were occupational stress (adjusted OR (aOR)=3.96, 95% CI 1.28 to 12.2), age ≥25 years (aOR=2.77, 95% CI 1.55 to 4.96), body mass index of 25-30 kg/m2 (aOR=1.71, 95% CI 1.32 to 2.2), body mass index >30 kg/m2 (aOR=2.74, 95% CI 1.84 to 4.09), permanent worker status (aOR=1.66, 95% CI 1.44 to 2.41) and seniority in the textile sector >5 years (aOR=2.18, 95% CI 1.7 to 2.8). Recognition at work emerged as an effect-modifying factor subject to stratification. CONCLUSIONS: Occupational factors, particularly job strain and recognition at work, are modifiable factors associated with hypertension in the ginning plants sector and deserve to be corrected through occupational health promotion and prevention.

[Prevalence and complications of gestational diabetes in women followed in Parakou maternities]. / Prévalence et complications du diabète gestationnel chez les femmes suivies dans les maternités de Parakou.

INTRODUCTION: The study was initiated to determine the prevalence and the complications of gestational diabetes in women attending Parakou maternities clinics in 2015. METHODS: This study was longitudinal, descriptive and analytical. The study population consists of women with gestational diabetes in Parakou maternities wards. The gestational diabetes was screened by the oral glucose tolerance test. The outcome of pregnancy was appreciated by the search for complications during pregnancy. Glycemic control was achieved in women 6 weeks after delivery. The data were analyzed using EPI-INFO 3.1 Fr. RESULTS: Of the 151 pregnant women who did the screening, 19 had a gestational diabetes; a prevalence of 12.6%. Pregnant women with gestational diabetes were at increased fetal macrosomia, hydramnios, macrosomia at birth, high birth weight of newborns compared to women without gestational diabetes (p<0,01). The maternal complications did not observed. The postprandial delivery blood glucose of women with gestational diabetes was normal. CONCLUSION: The gestational diabetes is associated with complications of pregnancy. Routine screening of women at risk for adequate management is necessary.

INTRODUCTION: L'étude a été initiée afin de déterminer la prévalence et les complications du diabète gestationnel (DG) chez les femmes suivies dans les maternités de Parakou en 2015. MÉTHODES: L'étude a été longitudinale, descriptive et analytique. La population d'étude est constituée des femmes souffrant de diabète gestationnel (DG) dans les maternités de Parakou. Le DG a été dépisté par l'épreuve d'hyperglycémie provoquée par voie orale. L'issue de la grossesse a été appréciée par la recherche de complications au cours de la grossesse. Un contrôle glycémique a été réalisé chez les femmes 6 semaines après l'accouchement. L'analyse des données a été faite par le logiciel EPI Data 3.1fr. RÉSULTATS: Parmi les 151 gestantes qui ont réalisé le dépistage, 19 ont un DG soit une prévalence de 12,6%. Les gestantes ayant un DG avaient plus de risque de macrosomie fœtale suspectée à l'échographie, d'hydramnios, de macrosomie à la naissance, de poids de naissance élevé des nouveaux-nés comparativement aux femmes n'ayant pas un diabète gestationnel (p<0,01). Il n'y avait pas de complications maternelles. La glycémie post prandiale du post partum des femmes ayant un DG était normale. CONCLUSION: Le DG est associé à des complications de la grossesse. Un dépistage systématique chez les femmes à risque en vue d'une prise en charge adéquate est nécessaire.

Occupational stress in industry setting in Benin 2019: A cross-sectional study.

BACKGROUND: Occupational stress is a psychosocial risk in the workplace. Working conditions in industrial settings may lead to occupational stress. In Benin, however, there is little epidemiological data on occupational stress in industrial settings. We aimed to determine the prevalence and factors associated with occupational stress in industrial settings in Benin in 2019. METHODS: This was a prospective, cross-sectional study conducted from January 31 to April 11, 2019, among 15 cotton ginning plants. Sampling was exhaustive for permanent workers and stratified in clusters by shift for occasional cotton gin workers. Data were collected through Karasek and Siegrist questionnaires. Data analysis was performed using R software. Binary multivariable logistic regression was performed. The significance level was p < 0.05. RESULTS: Of 1883 workers included, 90.8% were male. The median age was 38 years (IQR: 28 years to 49 years). The prevalence of occupational stress was 77.7% (95% CI: 75.8-79.6). Psychological demand was high in 93.0% of workers and 83.9% had low decision latitude. Among the workers, 16.3% had low social support and 89.9% had a low recognition score at work. Factors associated with occupational stress were: being an occasional vs. permanent worker (aOR 6.43, 95% CI 4.18 to 9.88); age less than 38 years (aOR 0.55, 95% CI 0.41 to 0.76); high intensity physical activity at work (aOR 1.33, 95% CI 1.03 to 1.73); working in production vs. administration (aOR 1.59, 95% CI 1.03 to 2.45); spending fewer than 4 years at the current work location (aOR 1.60, 95% CI 1.05 to 2.44); and scoring low for recognition at work (aOR 1.53, 95% CI 1.04 to 2.23). Noise exposure and being a shift worker were significant in univariable analysis, but not multivariable analysis. CONCLUSION: Occupational stress is very common among workers in industrial settings. The implementation and evaluation of preventive measures against these risk factors is necessary.

The dynamic clustering of insulin receptor underlies its signaling and is disrupted in insulin resistance.

Insulin receptor (IR) signaling is central to normal metabolic control and is dysregulated in metabolic diseases such as type 2 diabetes. We report here that IR is incorporated into dynamic clusters at the plasma membrane, in the cytoplasm and in the nucleus of human hepatocytes and adipocytes. Insulin stimulation promotes further incorporation of IR into these dynamic clusters in insulin-sensitive cells but not in insulin-resistant cells, where both IR accumulation and dynamic behavior are reduced. Treatment of insulin-resistant cells with metformin, a first-line drug used to treat type 2 diabetes, can rescue IR accumulation and the dynamic behavior of these clusters. This rescue is associated with metformin's role in reducing reactive oxygen species that interfere with normal dynamics. These results indicate that changes in the physico-mechanical features of IR clusters contribute to insulin resistance and have implications for improved therapeutic approaches.

Hijacking of transcriptional condensates by endogenous retroviruses.

Most endogenous retroviruses (ERVs) in mammals are incapable of retrotransposition; therefore, why ERV derepression is associated with lethality during early development has been a mystery. Here, we report that rapid and selective degradation of the heterochromatin adapter protein TRIM28 triggers dissociation of transcriptional condensates from loci encoding super-enhancer (SE)-driven pluripotency genes and their association with transcribed ERV loci in murine embryonic stem cells. Knockdown of ERV RNAs or forced expression of SE-enriched transcription factors rescued condensate localization at SEs in TRIM28-degraded cells. In a biochemical reconstitution system, ERV RNA facilitated partitioning of RNA polymerase II and the Mediator coactivator into phase-separated droplets. In TRIM28 knockout mouse embryos, single-cell RNA-seq analysis revealed specific depletion of pluripotent lineages. We propose that coding and noncoding nascent RNAs, including those produced by retrotransposons, may facilitate 'hijacking' of transcriptional condensates in various developmental and disease contexts.

A dual role for H2A.Z.1 in modulating the dynamics of RNA polymerase II initiation and elongation.

RNA polymerase II (RNAPII) pausing immediately downstream of the transcription start site is a critical rate-limiting step for the expression of most metazoan genes. During pause release, RNAPII encounters a highly conserved +1 H2A.Z nucleosome, yet how this histone variant contributes to transcription is poorly understood. Here, using an inducible protein degron system combined with genomic approaches and live cell super-resolution microscopy, we show that H2A.Z.1 modulates RNAPII dynamics across most genes in murine embryonic stem cells. Our quantitative analysis shows that H2A.Z.1 slows the rate of RNAPII pause release and consequently impacts negative elongation factor dynamics as well as nascent transcription. Consequently, H2A.Z.1 also impacts re-loading of the pre-initiation complex components TFIIB and TBP. Altogether, this work provides a critical mechanistic link between H2A.Z.1 and the proper induction of mammalian gene expression programs through the regulation of RNAPII dynamics and pause release.