Kremen1 regulates the regenerative capacity of support cells and mechanosensory hair cells in the zebrafish lateral line.

Mechanosensory hair cells in the inner ear mediate the sensations of hearing and balance, and in the specialized lateral line sensory system of aquatic vertebrates, the sensation of water movement. In mammals, hair cells lack the ability to regenerate following damage, resulting in sensory deficits. In contrast, non-mammalian vertebrates, such as zebrafish, can renew hair cells throughout their lifespan. Wnt signaling is required for development of inner ear and lateral line hair cells and regulates regeneration. Kremen1 inhibits Wnt signaling and hair cell formation, though its role in regeneration is unknown. We used a zebrafish kremen1 mutant line to show overactive Wnt signaling results in supernumerary support cells and hair cell regeneration without increased proliferation, in contrast with the previously described role of Wnt signaling during hair cell regeneration. This work allows us to understand the biology of mechanosensory hair cells and how regeneration might be promoted following damage.

Kremen1 regulates the regenerative capacity of support cells and mechanosensory hair cells in the zebrafish lateral line.

Mechanosensory hair cells in the inner ear mediate the sensations of hearing and balance, and in a specialize lateral line sensory system of aquatic vertebrates, the sensation of water movement. In mammals, hair cells lack the ability of regenerate following damage, resulting in sensory deficits. In contrast, non-mammalian vertebrates, such zebrafish, can renew hair cells throughout the life of the animal. Wnt signaling is required for development of inner ear and lateral line hair cells and regulates regeneration. Kremen1 inhibits Wnt signaling and hair cell formation, though its role in regeneration has not been established. We use a zebrafish kremen1 mutant line, to show that when Wnt signaling is overactivated in the lateral line, excessive regeneration occurs in the absence of increased proliferation, due to an increase in support cells. This contrasts with the previously described role of Wnt signaling during hair cell regeneration. This work will allow us to understand the biology of mechanosensory hair cells, and how regeneration might be promoted following damage.

Adjuvant vs. progression-triggered treatment with gemcitabine in platinum-ineligible high-risk bladder cancer patients: Long-term follow-up of a randomized phase 3 trial.

BACKGROUND: Cisplatin-based chemotherapy (ChT) is the preferred perioperative treatment in muscle-invasive urothelial carcinoma of the urinary bladder (UCUB). Nevertheless, a certain number of patients are ineligible for platinum-based ChT. This trial compared immediate adjuvant vs. delayed gemcitabine ChT at progression in platinum-ineligible patients with high-risk UCUB. METHODS: High-risk platinum-ineligible UCUB patients (n = 115) were randomized 1:1 to adjuvant gemcitabine (n = 59) or gemcitabine at progression (n = 56). Overall survival was analyzed. Additionally, we analyzed progression-free survival (PFS), toxicity and quality of life (QoL). RESULTS: After a median follow-up of 3.0 years (inter quartile range [IQR]: 1.3-11.6), adjuvant ChT did not significantly prolong overall survival (OS) (HR: 0.84; 95% CI: 0.57-1.24; P = 0.375), with 5-year OS of 44.1% (95% CI: 31.2-56.2) and 30.4% (95% CI: 19.0-42.5), respectively. We noted no significant difference in PFS (HR: 0.76; 95% CI: 0.49-1.18; P = 0.218), with 5-year PFS of 36.2% (95% CI: 22.8-49.7) in the adjuvant group and 22.2% (95% CI: 11.5%-35.1%) when treated at progression. Patients with adjuvant treatment showed a significantly worse QoL. The trial was prematurely closed after recruitment of 115 of the planned 178 patients. CONCLUSIONS: There was no statistically significant difference in terms of OS and PFS for patients with platinum-ineligible high-risk UCUB receiving adjuvant gemcitabine compared to patients treated at progression. These findings underline the importance of implementing and developing new perioperative treatments for platinum-ineligible UCUB patients.

The Role of STATs in Ovarian Cancer: Exploring Their Potential for Therapy.

Ovarian cancer (OvCa) is a deadly gynecologic malignancy that presents many clinical challenges due to late-stage diagnoses and the development of acquired resistance to standard-of-care treatment protocols. There is an increasing body of evidence suggesting that STATs may play a critical role in OvCa progression, resistance, and disease recurrence, and thus we sought to compile a comprehensive review to summarize the current state of knowledge on the topic. We have examined peer reviewed literature to delineate the role of STATs in both cancer cells and cells within the tumor microenvironment. In addition to summarizing the current knowledge of STAT biology in OvCa, we have also examined the capacity of small molecule inhibitor development to target specific STATs and progress toward clinical applications. From our research, the best studied and targeted factors are STAT3 and STAT5, which has resulted in the development of several inhibitors that are under current evaluation in clinical trials. There remain gaps in understanding the role of STAT1, STAT2, STAT4, and STAT6, due to limited reports in the current literature; as such, further studies to establish their implications in OvCa are necessitated. Moreover, due to the deficiency in our understanding of these STATs, selective inhibitors also remain elusive, and therefore present opportunities for discovery.

Effectiveness of an artificial intelligence-based system to curtail wind turbines to reduce eagle collisions.

Operating wind-power projects often includes protecting volant wildlife. One method for doing this uses an automated system to detect, identify (through use of artificial intelligence; AI), track animals (targets) and curtail turbines when risk of a collision is high. However, assessments of the effectiveness, in terms of identification accuracy and subsequent turbine curtailment of such systems are lacking. Over 1 year, we assessed such an automated system installed at a wind project in California, USA to determine its identification accuracy and rates at which "virtual" curtailments were ordered (without slowing turbines), for eagles (intended targets) and non-eagle targets. The system correctly identified 77% of eagles and 85% of non-eagles. Curtailment orders occurred 6 times more frequently for non-eagle targets (5,439) than for eagle targets (850). Greater abundance of common ravens that were misidentified as eagles influenced the effectiveness of the system by greatly increasing unintended curtailment orders. The balance between costs (price of the IdentiFlight system, reduced energy generation, turbine wear and maintenance) and benefits (reduced collisions between intended target species and turbines) may depend upon the biological setting, speed at which operators can curtail turbines, and the objectives of the operator when considering the IdentiFlight system.

Assessing barriers to access and equity for COVID-19 vaccination in the US.

BACKGROUND: Historical vaccination coverage in economically disadvantaged, ethnic minority, non-affluent white and agricultural populations in the US has lagged coverage in more affluent urban and suburban white populations due to a variety of social and economic factors. In the current COVID-19 pandemic, sociocultural and economic challenges continue to present significant obstacles to achieving equitable uptake of COVID-19 vaccines. The goal of this study was to qualitatively assess perceptions of key US healthcare stakeholders of the most significant barriers to COVID-19 vaccine access and equity to better characterize their expected impact on US communities. METHODS: After conducting a targeted literature review (TLR), we hypothesized 20 high-impact barriers which included structural and logistical barriers, capturing systemic challenges to vaccine accessibility, and attitudinal and informational barriers, affecting patient willingness to pursue vaccination. We developed a qualitative discussion guide, which included both open-ended and closed-ended questions, and interview stimulus material to conduct one-on-one in-depth interviews to assess the expected prevalence, severity, and persistence of these 20 high-impact barriers, which were hypothesized based on TLR. As a part of this qualitative study, we conducted one-on-one in-depth interviews with a diverse set of 15 US healthcare stakeholders who were involved in the COVID-19 vaccine rollout in states with relatively disparate vaccination rates by ethnicity. These stakeholders were selected to reflect an array of roles in the COVID-19 vaccine rollout, including infectious disease specialists, pharmacists, community advocacy representatives, and partners of local governments involved in the COVID-19 vaccine rollout and community education. RESULTS: Respondents identified limited vaccination sites in rural settings and technology-related barriers as the most prevalent and severe structural and logistical barriers in US communities. Respondents assessed COVID-19 vaccine safety concerns and politically motivated skepticism to be the most prevalent and severe attitudinal and informational barriers. Respondents cited proliferation of mobile vaccination clinics and local community messaging to endorse vaccines as the most effective solutions to these top structural and attitudinal barriers. Respondents expected politically motivated skepticism to be the most significant and persistent barrier to broader vaccine uptake in the US. CONCLUSIONS: Our study suggests that attitudinal barriers, particularly politically motivated skepticism, are likely to remain the most persistent challenges to widespread vaccination against COVID-19 in the US.

Physician perceptions of drug utilization management: Results of a national survey.

The use of drug utilization management techniques such as formulary exclusions, prior authorizations, and step edits has risen sharply during the last decade, contributing to the growing burden on physicians and patients. Limited quantitative data exist, however, on physician perceptions of drug utilization management. A national survey was conducted between February 9 and March 30, 2021, targeting office-based physicians working in the United States to assess their perceptions on drug utilization management in their practice. Of the 742 physicians that participated in the study, over 80% reported deciding against prescribing certain treatments in anticipation of drug utilization management at least sometimes (>50% of the time). Despite utilization management having an impact on prescribing decisions, about half of physicians said that the utilization management policies they encounter rarely or never (0-25% of the time) align with clinical evidence.

The Physician and Administrator-Reported Cost of Drug Utilization Management to Physician Practices: A Cross-Sectional Survey.

BACKGROUND: The use of drug utilization management techniques such as formulary exclusions, prior authorizations, and step edits has risen sharply during the last decade, contributing to growing administrative costs for physician practices. However, limited data exist on the extent of these administrative costs, with previous studies relying on data from over a decade ago. OBJECTIVE: The aim of this study was to assess physician and practice administrator experiences with drug utilization management. METHODS: A national survey was conducted between 9 February and 30 March 2021, targeting 925 physicians and administrators working at medical practices in the US. Time spent by physicians and their staff on tasks related to drug utilization management for prescription medications was collected and used to calculate the dollar value of that time. RESULTS: We estimated that physicians spent a median of 4.0 h per week on drug utilization management, while nurses spent 15.0 h and other staff spent between 3.6 and 10.0 h on drug utilization management per physician per week. This time was associated with a calculated median dollar value of $75,927 per physician per year. Extrapolating this estimate to a national scale suggests that time spent annually by physician practices on drug utilization management could be valued at more than $43 billion. CONCLUSIONS: Drug utilization management results in significant time spent by US physician practices, which in turn, results in meaningful costs to these practices. As the prevalence of drug utilization management continues to grow, the impact on physician practices will remain an important topic.

Value Frameworks in Oncology: Comparative Analysis and Implications to the Pharmaceutical Industry.

BACKGROUND: As the cost of oncology care continues to rise, composite value models that variably capture the diverse concerns of patients, physicians, payers, policymakers, and the pharmaceutical industry have begun to take shape. OBJECTIVES: To review the capabilities and limitations of 5 of the most notable value frameworks in oncology that have emerged in recent years and to compare their relative value and application among the intended stakeholders. METHODS: We compared the methodology of the American Society of Clinical Oncology (ASCO) Value Framework (version 2.0), the National Comprehensive Cancer Network Evidence Blocks, Memorial Sloan Kettering Cancer Center DrugAbacus, the Institute for Clinical and Economic Review Value Assessment Framework, and the European Society for Medical Oncology Magnitude of Clinical Benefit Scale, using a side-by-side comparative approach in terms of the input, scoring methodology, and output of each framework. In addition, we gleaned stakeholder insights about these frameworks and their potential real-world applications through dialogues with physicians and payers, as well as through secondary research and an aggregate analysis of previously published survey results. RESULTS: The analysis identified several framework-specific themes in their respective focus on clinical trial elements, breadth of evidence, evidence weighting, scoring methodology, and value to stakeholders. Our dialogues with physicians and our aggregate analysis of previous surveys revealed a varying level of awareness of, and use of, each of the value frameworks in clinical practice. For example, although the ASCO Value Framework appears nascent in clinical practice, physicians believe that the frameworks will be more useful in practice in the future as they become more established and as their outputs are more widely accepted. CONCLUSIONS: Along with patients and payers, who bear the burden of treatment costs, physicians and policymakers have waded into the discussion of defining value in oncology care, as well as pharmaceutical companies that seek to understand the impact of these value frameworks on each stakeholder, as they model the value and financial threshold of innovative, high-cost drugs.

Inhibiting Smad2/3 signaling in pluripotent mouse embryonic stem cells enhances endoderm formation by increasing transcriptional priming of lineage-specifying target genes.

BACKGROUND: Pluripotent embryonic stem cells (ESCs) offer great potential for regenerative medicine. However, efficient in vitro generation of specific desired cell types is still a challenge. We previously established that Smad2/3 signaling, essential for endoderm formation, regulates target gene expression by counteracting epigenetic repression mediated by Polycomb Repressive Complex 2 (PRC2). Although this mechanism has been demonstrated during differentiation and reprogramming, little is known of its role in pluripotent cells. RESULTS: Chromatin immunoprecipitation-deep sequencing of undifferentiated mouse ESCs inhibited for Smad2/3 signaling identified Prdm14, important for protecting pluripotency, as a target gene. Although Prdm14 accumulates the normally repressive PRC2 deposited histone modification H3K27me3 under these conditions, surprisingly, expression increases. Analysis indicates that increased H3K27me3 leads to increased binding of PRC2 accessory component Jarid2 and recruitment of RNA polymerase II. Similar increases were found at the Nodal endoderm target gene Eomes but it remained unexpressed in pluripotent cells as normal. Upon differentiation, however, Eomes expression was significantly higher than in cells that had not been inhibited for signaling before differentiation. In addition, endoderm formation was markedly increased. CONCLUSIONS: Blocking Smad2/3 signaling in pluripotent stem cells results in epigenetic changes that enhance the capacity for endoderm differentiation. Developmental Dynamics 245:807-815, 2016. © 2016 Wiley Periodicals, Inc.

Nodal signaling from the visceral endoderm is required to maintain Nodal gene expression in the epiblast and drive DVE/AVE migration.

In the early mouse embryo, a specialized population of extraembryonic visceral endoderm (VE) cells called the distal VE (DVE) arises at the tip of the egg cylinder stage embryo and then asymmetrically migrates to the prospective anterior, recruiting additional distal cells. Upon migration these cells, called the anterior VE (AVE), establish the anterior posterior (AP) axis by restricting gastrulation-inducing signals to the opposite pole. The Nodal-signaling pathway has been shown to have a critical role in the generation and migration of the DVE/AVE. The Nodal gene is expressed in both the VE and in the pluripotent epiblast, which gives rise to the germ layers. Previous findings have provided conflicting evidence as to the relative importance of Nodal signaling from the epiblast vs. VE for AP patterning. Here we show that conditional mutagenesis of the Nodal gene specifically within the VE leads to reduced Nodal expression levels in the epiblast and incomplete or failed DVE/AVE migration. These results support a required role for VE Nodal to maintain normal levels of expression in the epiblast, and suggest signaling from both VE and epiblast is important for DVE/AVE migration.

Isolation of rare recombinants without using selectable markers for one-step seamless BAC mutagenesis.

Current methods to isolate rare (1:10,000-1:100,000) bacterial artificial chromosome (BAC) recombinants require selectable markers. For seamless BAC mutagenesis, selectable markers need to be removed after isolation of recombinants through counterselection. Here we illustrate founder principle-driven enrichment (FPE), a simple method to rapidly isolate rare recombinants without using selectable markers, allowing one-step seamless BAC mutagenesis. As proof of principle, we isolated 1:100,000 seamless fluorescent protein-modified Nodal BACs and confirmed BAC functionality by generating fluorescent reporter mice. We also isolated small indel P1 phage-derived artificial chromosome (PAC) and BAC recombinants. Statistical analysis revealed that 1:100,000 recombinants can be isolated with <40 PCRs, and we developed a web-based calculator to optimize FPE.

Loss of function of mouse Pax-Interacting Protein 1-associated glutamate rich protein 1a (Pagr1a) leads to reduced Bmp2 expression and defects in chorion and amnion development.

BACKGROUND: Human PAX-Interacting Protein 1 (PAXIP1)-associated glutamate rich protein 1 (PAGR1, also known as PA1) originally was discovered as part of a complex containing PAXIP1 and histone H3K4 methyltransferases MLL3 and MLL4, suggesting a role in epigenetic gene regulation. Further in vitro studies suggested additional functions in DNA damage repair and transcription. However, in vivo analysis of PAGR1 function has been lacking. RESULTS: Here we show that expression of the cognate mouse gene Pagr1a is found predominately in the extraembryonic and chorionic ectoderm from pregastrulation stages and is up-regulated within the embryo proper after gastrulation. Embryos with a germ line deletion of Pagr1a establish the anterior-posterior axis, and show normal neuroectodermal, mesodermal, and endodermal patterning, but fail to develop beyond the four- to five-somite stage or to undergo axial rotation. Pagr1a(-) (/) (-) embryos also show abnormal development of extraembryonic tissues with defects seen in the amnion, chorion and visceral yolk sac. At the molecular level, Pagr1a(-) (/) (-) embryos have reduced expression of BMP2, a known regulator of extraembryonic development. CONCLUSIONS: Loss of mouse Pagr1a function leads to defective extraembryonic development, likely due at least in part to altered BMP signaling, contributing to developmental arrest.

Senp1 is essential for desumoylating Sumo1-modified proteins but dispensable for Sumo2 and Sumo3 deconjugation in the mouse embryo.

Posttranslational modification with small ubiquitin-like modifier (Sumo) regulates numerous cellular and developmental processes. Sumoylation is dynamic with deconjugation by Sumo-specific proteases (Senps) regulating steady-state levels. Different Senps are found in distinct subcellular domains, which may limit their deconjugation activity to colocalizing Sumo-modified proteins. In vitro, Senps can discriminate between the different Sumo paralogs: Sumo1 versus the highly related Sumo2 and Sumo3 (Sumo2/3), which can form poly-Sumo chains. However, a full understanding of Senp specificity in vivo is still lacking. Here, using biochemical and genetic approaches, we establish that Senp1 has an essential, nonredundant function to desumoylate Sumo1-modified proteins during mouse embryonic development. Senp1 specificity for Sumo1 conjugates represents an intrinsic function and not simply a product of colocalization. In contrast, Senp1 has only a limited role in Sumo2/3 desumoylation, although it may regulate Sumo1-mediated termination of poly-Sumo2/3 chains.

Polycomb determines responses to smad2/3 signaling in embryonic stem cell differentiation and in reprogramming.

Integration of extrinsic signals, epigenetic regulators, and intrinsic transcription factors establishes pluripotent stem cell identity. Interplay between these components also underlies the capacity of stem cells to undergo differentiation, and of differentiated cells to re-establish the pluripotent state in direct reprogramming. Polycomb repressive complexes are epigenetic regulators that play key roles in stem cell identity and in differentiated cell fates. Smad2 and Smad3 (Smad2/3), the intracellular mediators of the Nodal/Activin/transforming growth factor (TGF) ß cell-cell signaling pathway also are implicated in stem cell pluripotency and in differentiation. Here, we show that Polycomb imposes responses to Smad2/3-mediated signaling to selectively regulate expression of the master pluripotency factor Oct 4 during initiation of differentiation, but not in the self-renewing pluripotent ground state. During reprogramming back to the ground state, we find that the enhancement of reprogramming efficiency stemming from blocking Nodal/Activin/TGFß signaling also depends on Polycomb. These context-dependent responses to Smad2/3 imposed by Polycomb action provide a mechanism for selective gene regulation that can reconcile the apparently conflicting roles of this signaling pathway in pluripotency, differentiation, and reprogramming.

Sonic hedgehog signaling directly targets Hyaluronic Acid Synthase 2, an essential regulator of phalangeal joint patterning.

Sonic hedgehog (Shh) signal, mediated by the Gli family of transcription factors, plays an essential role in the growth and patterning of the limb. Through analysis of the early limb bud transcriptome, we identified a posteriorly-enriched gene, Hyaluronic Acid Synthase 2 (Has2), which encodes a key enzyme for the synthesis of hyaluronan (HA), as a direct target of Gli transcriptional regulation during early mouse limb development. Has2 expression in the limb bud is lost in Shh null and expanded anteriorly in Gli3 mutants. We identified an ∼3kb Has2 promoter fragment that contains two strong Gli-binding consensus sequences, and mutation of either site abrogated the ability of Gli1 to activate Has2 promoter in a cell-based assay. Additionally, this promoter fragment is sufficient to direct expression of a reporter gene in the posterior limb mesenchyme. Chromatin immunoprecipitation of DNA-Gli3 protein complexes from limb buds indicated that Gli3 strongly binds to the Has2 promoter region, suggesting that Has2 is a direct transcriptional target of the Shh signaling pathway. We also showed that Has2 conditional mutant (Has2cko) hindlimbs display digit-specific patterning defects with longitudinally shifted phalangeal joints and impaired chondrogenesis. Has2cko limbs show less capacity for mesenchymal condensation with mislocalized distributions of chondroitin sulfate proteoglycans (CSPGs), aggrecan and link protein. Has2cko limb phenotype displays striking resemblance to mutants with defective chondroitin sulfation suggesting tight developmental control of HA on CSPG function. Together, our study identifies Has2 as a novel downstream target of Shh signaling required for joint patterning and chondrogenesis.

A one-step miniprep for the isolation of plasmid DNA and lambda phage particles.

Plasmid DNA minipreps are fundamental techniques in molecular biology. Current plasmid DNA minipreps use alkali and the anionic detergent SDS in a three-solution format. In addition, alkali minipreps usually require additional column-based purification steps and cannot isolate other extra-chromosomal elements, such as bacteriophages. Non-ionic detergents (NIDs) have been used occasionally as components of multiple-solution plasmid DNA minipreps, but a one-step approach has not been developed. Here, we have established a one-tube, one-solution NID plasmid DNA miniprep, and we show that this approach also isolates bacteriophage lambda particles. NID minipreps are more time-efficient than alkali minipreps, and NID plasmid DNA performs better than alkali DNA in many downstream applications. In fact, NID crude lysate DNA is sufficiently pure to be used in digestion and sequencing reactions. Microscopic analysis showed that the NID procedure fragments E. coli cells into small protoplast-like components, which may, at least in part, explain the effectiveness of this approach. This work demonstrates that one-step NID minipreps are a robust method to generate high quality plasmid DNA, and NID approaches can also isolate bacteriophage lambda particles, outperforming current standard alkali-based minipreps.

Persistence of host defence behaviour in the absence of avian brood parasitism.

The fate of host defensive behaviour in the absence of selection from brood parasitism is critical to long-term host-parasite coevolution. We investigated whether New World Bohemian waxwings Bombycilla garrulus that are allopatric from brown-headed cowbird Molothrus ater and common cuckoo Cuculus canorus parasitism have retained egg rejection behaviour. We found that egg rejection was expressed by 100 per cent of Bohemian waxwings. Our phylogeny revealed that Bohemian and Japanese waxwings Bombycilla japonica were sister taxa, and this clade was sister to the cedar waxwing Bombycilla cedrorum. In addition, there was support for a split between Old and New World Bohemian waxwings. Our molecular clock estimates suggest that egg rejection may have been retained for 2.8-3.0 Myr since New World Bohemian waxwings inherited it from their common ancestor with the rejecter cedar waxwings. These results support the 'single trajectory' model of host-brood parasite coevolution that once hosts evolve defences, they are retained, forcing parasites to become more specialized over time.

Hofmeister series salts enhance purification of plasmid DNA by non-ionic detergents.

Ion-exchange chromatography is the standard technique used for plasmid DNA purification, an essential molecular biology procedure. Non-ionic detergents (NIDs) have been used for plasmid DNA purification, but it is unclear whether Hofmeister series salts (HSS) change the solubility and phase separation properties of specific NIDs, enhancing plasmid DNA purification. After scaling-up NID-mediated plasmid DNA isolation, we established that NIDs in HSS solutions minimize plasmid DNA contamination with protein. In addition, large-scale NID/HSS solutions eliminated lipopolysaccharides (LPS) contamination of plasmid DNA more effectively than Qiagen ion-exchange columns. Large-scale NID isolation/NID purification generated increased yields of high-quality DNA compared to alkali isolation/column purification. This work characterizes how HSS enhance NID-mediated plasmid DNA purification, and demonstrates that NID phase transition is not necessary for LPS removal from plasmid DNA. Specific NIDs such as IGEPAL CA-520 can be utilized for rapid, inexpensive, and efficient laboratory-based large-scale plasmid DNA purification, outperforming Qiagen-based column procedures.

Nodal signaling recruits the histone demethylase Jmjd3 to counteract polycomb-mediated repression at target genes.

Both intercellular signaling and epigenetic mechanisms regulate embryonic development, but it is unclear how they are integrated to establish and maintain lineage-specific gene expression programs. Here, we show that a key function of the developmentally essential Nodal-Smads2/3 (Smad2 and Smad3) signaling pathway is to recruit the histone demethylase Jmjd3 to target genes, thereby counteracting repression by Polycomb. Smads2/3 bound to Jmjd3 and recruited it to chromatin in a manner that was dependent on active Nodal signaling. Knockdown of Jmjd3 alone substantially reduced Nodal target gene expression, whereas in the absence of Polycomb, target loci were expressed independently of Nodal signaling. These data establish a role for Polycomb in imposing a dependency on Nodal signaling for the expression of target genes and reveal how developmental signaling integrates with epigenetic processes to control gene expression.