Characteristics and treatment of acute myeloid neoplasms with cutaneous involvement in infants up to 6 months of age: A retrospective study

BACKGROUND

Myeloid neoplasms account for 50% of cases of pediatric leukemias in infants. Approximately 25%-50% of patients with newborn leukemia have cutaneous extramedullary disease (EMD). In less than 10% of patients, aleukemic leukemia cutis or isolated extramedullary disease with cutaneous involvement (cEMD) occurs when skin lesions appear prior to bone marrow involvement and systemic symptoms. Interestingly, in acute myeloid leukemia with cutaneous EMD (AML-cEMD) and cEMD, spontaneous remissions have been reported.

METHOD

This is a multicentric retrospective cohort study aiming to describe characteristics, treatment, and outcome of infants with either cEMD or presence of cutaneous disease with involvement of the bone marrow (AML-cEMD). This study included patients born between 1990 and 2018 from Italy, the Netherlands, Switzerland, and the United States, diagnosed between 0 and 6 months of life with cEMD or AML-cEMD. Descriptive statistics, Fisher's exact test, Kaplan-Meier method, and log rank test were applied.

RESULTS

The cohort consisted of n = 50 patients, including 42 AML-cEMD and eight cEMD patients. The most common genetic mutation found was a KMT2A rearrangement (n = 26, 52%). Overall 5-year event-free survival (EFS) and overall survival (OS) were 66% [confidence interval (CI): 51-78] and 75% [CI: 60-85], respectively. In two patients, complete spontaneous remission occurred without any therapy. Central nervous system (CNS) involvement was found in 25% of cEMD patients. No difference in outcomes was observed between the AML-cEMD and cEMD groups, but none of the latter patients included in the study died. KMT2A rearrangements were not associated with poorer prognosis.

CONCLUSION

In the largest cohort to date, our study describes the characteristics of infants with cutaneous involvement of myeloid neoplasms including cytomolecular findings and survival rates. Further prospective biologic and clinical studies of these infants with myeloid neoplasms will be required to individualize therapy for this rare patient population.

CIC-DUX4 Chromatin Profiling Reveals New Epigenetic Dependencies and Actionable Therapeutic Targets in CIC-Rearranged Sarcomas

CIC-DUX4-rearranged sarcoma (CDS) is a rare and aggressive soft tissue tumor that occurs most frequently in young adults. The key oncogenic driver of this disease is the expression of the CIC-DUX4 fusion protein as a result of chromosomal rearrangements. CIC-DUX4 displays chromatin binding properties, and is therefore believed to function as an aberrant transcription factor. However, the chromatin remodeling events induced by CIC-DUX4 are not well understood, limiting our ability to identify new mechanism-based therapeutic strategies for these patients. Here, we generated a genome-wide profile of CIC-DUX4 DNA occupancy and associated chromatin states in human CDS cell models and primary tumors. Combining chromatin profiling, proximity ligation assays, as well as genetic and pharmacological perturbations, we show that CIC-DUX4 operates as a potent transcriptional activator at its binding sites. This property is in contrast with the repressive function of the wild-type CIC protein, and is mainly mediated through the direct interaction of CIC-DUX4 with the acetyltransferase p300. In keeping with this, we show p300 to be essential for CDS tumor cell proliferation; additionally, we find its pharmacological inhibition to significantly impact tumor growth in vitro and in vivo. Taken together, our study elucidates the mechanisms underpinning CIC-DUX4-mediated transcriptional regulation.

Assessment of Dietary Iron Intake and Sources in Early Childhood in a Nationally Representative Cross-Sectional Survey

BACKGROUND

Iron deficiency has particular importance in early childhood because of its impact on growth and development. Preventive food-based strategies of iron deficiency require knowledge of intakes and sources of iron.

OBJECTIVE

This study aimed to assess daily iron intakes (DIIs) in 2013, to compare them with the dietary reference values, to assess their evolution since 1981, and to identify iron food sources among nonbreastfed French children younger than 3 years.

DESIGN

This was a nationwide cross-sectional survey conducted in 2013 in France to assess DIIs by means of comparing them with the dietary reference values. Parents' reported diet diaries were collected for 3 nonconsecutive days.

PARTICIPANTS/SETTING

Of the 1,184 children enrolled in the study, 1,035 nonbreastfed healthy children aged 0.5 to 35 months stratified into 11 age groups were included after informed consent was obtained from parents and according to a weighted quota sampling method.

MAIN OUTCOME MEASURES

DII from the different food sources and trends in their evolution from 1981 to 2013 was assessed.

STATISTICAL ANALYSES PERFORMED

Results are expressed as median with interquartile range and range and mean ± SD. Student t test was used with the 2-sided α level of significance set at 5%.

RESULTS

Mean ± SD DII was 6.7 ± 2.3 mg/d before 6 months, 8.2 ± 2.7 mg/d from 6 months to 1 year, and 7.0 ± 3.2 mg/d from 1 to 3 years. The prevalence of infants older than 7 months with a DII less than the dietary reference values was 52.5%, and that of young children was 30%. After slightly increasing until 2005, DIIs decreased thereafter. Formulas contributed to most of the DIIs up to 2 years of age. Cereals were the second largest contributor to DIIs, and meat accounted for a small part of iron intake.

CONCLUSIONS

A substantial number of children between 6 months and 3 years of age were at risk of insufficient iron intake. This risk increased from 2005 to 2013. The role of formula in ensuring iron intake is highlighted. More research on health outcomes of low iron intakes is needed.

PSTPIP1-Associated Myeloid-Related Proteinemia Inflammatory (PAMI) Syndrome: A Systematic Review

PSTPIP1 (proline-serine-threonine phosphatase-interactive protein 1)-associated myeloid-related proteinemia inflammatory (PAMI) syndrome, previously known as Hyperzincemia/Hypercalprotectinemia (Hz/Hc) syndrome, is a recently described, rare auto-inflammatory disorder caused by specific deleterious variants in the PSTPIP1 gene (p.E250K and p.E257K). The disease is characterized by chronic systemic inflammation, cutaneous and osteoarticular manifestations, hepatosplenomegaly, anemia, and neutropenia. Increased blood levels of MRP 8/14 and zinc distinguish this condition from other PSTPIP1-associated inflammatory diseases (PAID). The aim of this systematic review is to provide a comprehensive overview of the disease phenotype, course, treatment, and outcome based on reported cases. This systematic review adheres to the PRISMA guidelines (2020) for reporting. A literature search was performed in Embase, Medline, and Web of Science on 13 October 2022. The quality of the case reports and case series was assessed using the JBI checklists. Out of the 43 included patients with PAMI syndrome, there were 24 females and 19 males. The median age at onset was 3.9 years. The main clinical manifestations included anemia (100%), neutropenia (98%), cutaneous manifestations (74%), osteoarticular manifestations (72%), splenomegaly (70%), growth failure (57%), fever (51%), hepatomegaly (56%), and lymphadenopathy (39%). Systemic inflammation was described in all patients. Marked elevation of zinc and MRP 8/14 blood levels were observed in all tested patients. Response to treatment varied and no consistently effective therapy was identified. The most common therapeutic options were corticosteroids (N = 30), anakinra (N = 13), cyclosporine A (N = 11), canakinumab (N = 6), and anti-TNF (N = 14). Hematopoietic stem cell transplantation has been recently reported to be successful in five patients. Our review highlights the key characteristics of PAMI syndrome and the importance of considering this disease in the differential diagnosis of patients presenting with early-onset systemic inflammation and cytopenia.

Hematological variations in healthy participants exposed 2 h to propylene glycol ethers under controlled conditions

Glycol ethers are solvents used in a plethora of occupational and household products exposing the users to potential toxic effects. Several glycol ethers derived from ethylene glycol induce hematological toxicity, such as anemia in workers. The exposure effects on blood cells of glycol ethers derived from propylene glycol are unknown in humans. The aim of our study was to evaluate blood parameters indicative of red blood cell (RBC) hemolysis and oxidative stress in participants exposed to propylene glycol (propylene glycol monobutyl ether (PGBE) and propylene glycol monomethyl ether (PGME)), two extensively used propylene glycol derivatives worldwide. Seventeen participants were exposed 2 h in a control inhalation exposure chamber to low PGME (35 ppm) and PGBE (15 ppm) air concentrations. Blood was regularly collected before, during (15, 30, 60, and 120 min), and 60 min after exposure for RBC and oxidative stress analyses. Urine was also collected for clinical effects related to hemolysis. Under the study conditions, our results showed that the blood parameters such as RBCs, hemoglobin concentration, and white blood cells tended to increase in response to PGME and PGBE exposures. These results raise questions about the possible effects in people regularly exposed to higher concentrations, such as workers.

Highly connected 3D chromatin networks established by an oncogenic fusion protein shape tumor cell identity

Cell fate transitions observed in embryonic development involve changes in three-dimensional genomic organization that provide proper lineage specification. Whether similar events occur within tumor cells and contribute to cancer evolution remains largely unexplored. We modeled this process in the pediatric cancer Ewing sarcoma and investigated high-resolution looping and large-scale nuclear conformation changes associated with the oncogenic fusion protein EWS-FLI1. We show that chromatin interactions in tumor cells are dominated by highly connected looping hubs centered on EWS-FLI1 binding sites, which directly control the activity of linked enhancers and promoters to establish oncogenic expression programs. Conversely, EWS-FLI1 depletion led to the disassembly of these looping networks and a widespread nuclear reorganization through the establishment of new looping patterns and large-scale compartment configuration matching those observed in mesenchymal stem cells, a candidate Ewing sarcoma progenitor. Our data demonstrate that major architectural features of nuclear organization in cancer cells can depend on single oncogenes and are readily reversed to reestablish latent differentiation programs.

Predictive Factors for the Occurrence of Perioperative Complications in Pediatric Posterior Fossa Tumors

OBJECTIVE

Central nervous system tumors are the most common solid neoplasm in children, 60%-70% occurring in the posterior fossa. Surgery is the mainstay of treatment but surgery in the pediatric population is associated with a high risk of perioperative complications. We aimed at analyzing the perioperative complications after posterior fossa surgery in a pediatric population and identifying the associated risk factors.

METHODS

Retrospective study of all pediatric patients undergoing surgery for resection of a posterior fossa tumor between 1999 and 2019, at the University Hospital of Lausanne. Data were collected including age, clinical presentation, tumor localization, presence of preoperative hydrocephalus, timing of surgery, surgical approach, surgical team, extent of surgical resection, perisurgical complications, and histopathological diagnosis. Statistical analysis was performed to correlate the data with the risk of complications.

RESULTS

Sixty-seven patients were included. Perisurgical complications were identified in 39 patients (58.2%), of which 14 (35.9%) required corrective interventions. The perioperative mortality rate was zero. In the univariate analysis, surgery performed under emergency conditions, transvermian and telovelar approaches were statistically correlated with an increased rate of complications. Extent of resection, hydrocephalus, and Lansky index at presentation were not predictive of perioperative complications. Midline tumor, tumor volume >25 cm³, and surgery performed by a nonspecialized pediatric onconeurosurgeon were found to be independent risk factors in the multivariate analysis.

CONCLUSIONS

Surgery in the posterior fossa in the pediatric population harbors a high risk of complications. Identifying the variables contributing to these complications is important in order to improve surgical management of these patients.

In vitro-transfusional model for red-blood-cell study: the advantage of lowering hematocrit

BACKGROUND

The quality of red blood cells (RBCs) stored in red cell concentrates (RCCs) is influenced by processing, storage and donor characteristics, and can have a clinical impact on transfused patients. To evaluate RBC properties and their potential impact in a transfusion setting, a simple in vitro-transfusional model has been developed.

MATERIALS AND METHODS

Transfusion was simulated by mixing a washed RBC pool from two male-derived RCCs stored at 4°C with a pool of 15 male-derived fresh frozen plasma (FFP) units, representing the recipient, at a hematocrit (HCT) of 30% ("control" setting) or 5% (alternative model). The mixtures were incubated at 37°C, 5% of CO₂ up to 48 h. Different metabolites, hemolysis and microvesicles (MVs) were quantified at several incubation times and RBC-morphology changes and deformability after incubation. For each model, biological triplicates have been investigated with RCCs at storage days 2 and 43.

RESULTS

The 5%-HCT model restored the 2,3-DPG level and maintained the ATP level. Furthermore, glucose consumption and corresponding lactate production were increased in the 5%- vs the 30%-HCT condition. Lower hemolysis was observed with 5%-HCT, but only at day 2. However, morphological analysis by digital holographic microscopy (DHM) revealed a decreased fraction of discocytes at 5% rather than at 30% of HCT at storage day 2 but at day 43, the trend was inverted. Concordantly, RBCs incubated at 5% of HCT were more deformable than at 30% at day 43 (p<0.0001).

DISCUSSION

Higher metabolic activity of RBCs in the 5%-HCT condition was promoted by a higher glucose availability and limited cell-waste accumulation. The conditions of the new proposed model thus enabled rejuvenation of RBCs and maintained them in a physiological-close state in contrast to the 30%-HCT model. It may be used as a first approach to evaluate e.g., the impact of donor and recipient characteristics on RBC properties.

PASTEC - a prospective, single-center, randomized, cross-over trial of pure physical versus physical plus attentional training in children with cancer

Despite recent improvements in survival rates in children with cancer, long-term toxicities remain a major concern. Physical activity could reduce the impact of long-term sequelae, notably in neuropsychological and physical areas. We report of a randomized trial of pure physical versus physical/attentional training in pediatric oncology patients. Twenty-two patients aged 6-18 y.o. were included, irrespective of their clinical diagnosis or treatment status, stratified by age and randomized 1:1 into pure physical vs. physical/attentional activity arms, with a cross-over at study midpoint. Neurological, motor and neuropsychological assessments were performed at inclusion, start, crossover and end of the program. Feasibility, defined as > 80% patients attending > 80% of sessions, was the primary endpoint. Secondary outcomes were improvements in neuropsychological and motor performance tests. While 68% of patients attended more than 80% of sessions during the pre-crossover phase of the study, this dropped to 36% post-crossover. Our study therefore failed to meet our primary endpoint. Nonetheless, significant improvements in anxiety (p<0.001), emotional control (p = 0.04), organization skills (p = 0.03), as well as motor deficit scores (p = 0.04) were observed. We noted no significant difference between the pure physical and the physical/attentional training arms, or when analyzing subgroups by age or sequence of intervention. We conclude that physical activity has a positive impact on anxiety, emotional and organizational aspects as well as motor deficits. Attendance dropped during the course of the study and motivational interventions should be included in future studies or equivalent programs.Supplemental data for this article is available online at https://doi.org/10.1080/08880018.2021.1994677 .

TWIST1 expression is associated with high-risk neuroblastoma and promotes primary and metastatic tumor growth

The embryonic transcription factors TWIST1/2 are frequently overexpressed in cancer, acting as multifunctional oncogenes. Here we investigate their role in neuroblastoma (NB), a heterogeneous childhood malignancy ranging from spontaneous regression to dismal outcomes despite multimodal therapy. We first reveal the association of TWIST1 expression with poor survival and metastasis in primary NB, while TWIST2 correlates with good prognosis. Secondly, suppression of TWIST1 by CRISPR/Cas9 results in a reduction of tumor growth and metastasis colonization in immunocompromised mice. Moreover, TWIST1 knockout tumors display a less aggressive cellular morphology and a reduced disruption of the extracellular matrix (ECM) reticulin network. Additionally, we identify a TWIST1-mediated transcriptional program associated with dismal outcome in NB and involved in the control of pathways mainly linked to the signaling, migration, adhesion, the organization of the ECM, and the tumor cells versus tumor stroma crosstalk. Taken together, our findings confirm TWIST1 as promising therapeutic target in NB.

Multiple neonicotinoids in children's cerebro-spinal fluid, plasma, and urine

BACKGROUND

Neonicotinoids (NN) are selective neurotoxic pesticides that bind to insect but also mammal nicotinic acetycholine receptors (nAChRs). As the most widely used class of insecticides worldwide, they are ubiquitously found in the environment, wildlife, and foods, and thus of special concern for their impacts on the environment and human health. nAChRs are vital to proper brain organization during the prenatal period and play important roles in various motor, emotional, and cognitive functions. Little is known on children's contamination by NN. In a pilot study we tested the hypothesis that children's cerebro-spinal fluid (CSF) can be contaminated by NN.

METHODS

NN were analysed in leftover CSF, blood, and urine samples from children treated for leukaemias and lymphomas and undergoing therapeutic lumbar punctions. We monitored all neonicotinoids approved on the global market and some of their most common metabolites by ultra-high performance liquid chromatography-tandem mass spectrometry.

RESULTS

From August to December 2020, 14 children were consecutively included in the study. Median age was 8 years (range 3-18). All CSF and plasma samples were positive for at least one NN. Nine (64%) CSF samples and 13 (93%) plasma samples contained more than one NN. Thirteen (93%) CSF samples had N-desmethyl-acetamiprid (median concentration 0.0123, range 0.0024-0.1068 ng/mL), the major metabolite of acetamiprid. All but one urine samples were positive for ≥ one NN. A statistically significant linear relationship was found between plasma/urine and CSF N-desmethyl-acetamiprid concentrations.

CONCLUSIONS

We have developed a reliable analytical method that revealed multiple NN and/or their metabolites in children's CSF, plasma, and urine. Our data suggest that contamination by multiple NN is not only an environmental hazard for non-target insects such as bees but also potentially for children.

Congenital X-linked neutropenia with myelodysplasia and somatic tetraploidy due to a germline mutation in SEPT6

Septins play key roles in mammalian cell division and cytokinesis but have not previously been implicated in a germline human disorder. A male infant with severe neutropenia and progressive dysmyelopoiesis with tetraploid myeloid precursors was identified. No known genetic etiologies for neutropenia or bone marrow failure were found. However, next-generation sequencing of germline samples from the patient revealed a novel, de novo germline stop-loss mutation in the X-linked gene SEPT6 that resulted in reduced SEPT6 staining in bone marrow granulocyte precursors and megakaryocytes. Patient skin fibroblast-derived induced pluripotent stem cells (iPSCs) produced reduced myeloid colonies, particularly of the granulocyte lineage. CRISPR/Cas9 knock-in of the patient's mutation or complete knock-out of SEPT6 was not tolerated in non-patient-derived iPSCs or human myeloid cell lines, but SEPT6 knock-out was successful in an erythroid cell line and resulting clones revealed a propensity to multinucleation. In silico analysis predicts that the mutated protein hinders the dimerization of SEPT6 coiled-coils in both parallel and antiparallel arrangements, which could in turn impair filament formation. These data demonstrate a critical role for SEPT6 in chromosomal segregation in myeloid progenitors that can account for the unusual predisposition to aneuploidy and dysmyelopoiesis.

The landscape of pediatric Diamond-Blackfan anemia in Switzerland: genotype and phenotype characteristics

Diamond-Blackfan anemia (DBA) is caused mainly by genetic mutations in large (RPL) or small ribosomal subunit genes (RPS) and presents with macrocytic anemia and congenital malformations. Clinical differences between genotypes are insufficiently understood. The aim of this study was to assess clinical features, treatment strategies, and genotypes in the Swiss pediatric DBA population. We retrospectively reviewed medical charts of pediatric patients with DBA in Switzerland and stratified patients by RPL versus RPS mutations. We report 17 DBA patients in Switzerland who were all genetically investigated. In our cohort, patients showed a wide spectrum of clinical presentations and treatment needs. We found a high proportion of physical malformations (77%) including lower limb (17%) and anorectal (12%) malformations. The two patients with anorectal malformations presented both with antepositioning of the anus needing surgery within the first 15 months of life. One of these patients had sphincteric dysfunction, the other coccygeal agenesis. We found that included patients with an RPL mutation more frequently tended to have physical malformations and a milder anemia compared to patients with an RPS mutation (median hemoglobin at diagnosis 76 g/l versus 22 g/l).Conclusion: We illustrate the wide clinical and genetic spectrum of DBA in Switzerland. Our findings highlight the need to take this diagnosis into consideration in patients with severe anemia but also in patients with mild anemia where malformations are present. Lower limb and anorectal malformation extend the spectrum of DBA-associated malformations. What is Known? • There is a large variation in the phenotype of Diamond-Blackfan Anemia (DBA) and diversity of genetic mutations. • Malformation of the upper limbs, head and face, heart, and genitourinary system is frequently identified. What is New? • Patients with lower limb and anorectal malformations were repetitively found in our cohort enlarging the clinical spectrum of malformations. • We show two patients of the same family with a DBA-like condition where the same RPL17 variant was identified.

Recapitulation of erythropoiesis in congenital dyserythropoietic anaemia type I (CDA-I) identifies defects in differentiation and nucleolar abnormalities

The investigation of inherited disorders of erythropoiesis has elucidated many of the principles underlying the production of normal red blood cells and how this is perturbed in human disease. Congenital Dyserythropoietic Anaemia type 1 (CDA-I) is a rare form of anaemia caused by mutations in two genes of unknown function: CDAN1 and CDIN1 (previously called C15orf41), whilst in some cases, the underlying genetic abnormality is completely unknown. Consequently, the pathways affected in CDA-I remain to be discovered. To enable detailed analysis of this rare disorder we have validated a culture system which recapitulates all of the cardinal haematological features of CDA-I, including the formation of the pathognomonic 'spongy' heterochromatin seen by electron microscopy. Using a variety of cell and molecular biological approaches we discovered that erythroid cells in this condition show a delay during terminal erythroid differentiation, associated with increased proliferation and widespread changes in chromatin accessibility. We also show that the proteins encoded by CDAN1 and CDIN1 are enriched in nucleoli which are structurally and functionally abnormal in CDA-I. Together these findings provide important pointers to the pathways affected in CDA-I which for the first time can now be pursued in the tractable culture system utilised here.

A live single-cell reporter assay links intratumor heterogeneity to metastatic proclivity in Ewing sarcoma

Targeting of the most aggressive tumor cell subpopulations is key for effective management of most solid malignancies. However, the metastable nature of tumor heterogeneity, which allows cells to transition between strong and weak tumorigenic phenotypes, and the lack of reliable markers of tumor-promoting properties hamper identification of the most relevant cells. To overcome these obstacles, we designed a functional microRNA (miR)-based live-cell reporter assay to identify highly tumorigenic cells in xenotransplants of primary Ewing sarcoma (EwS) 3D cultures. Leveraging the inverse relationship between cell pluripotency and miR-145 expression, we successfully separated highly tumorigenic, metastasis-prone (miR-145low) cells from poorly tumorigenic, nonmetastatic (miR-145high) counterparts. Gene expression and functional studies of the two cell populations identified the EPHB2 receptor as a prognostic biomarker in patients with EwS and a major promoter of metastasis. Our study provides a simple and powerful means to identify and isolate tumor cells that display aggressive behavior.

Biomarkers for the central nervous system complications of sickle cell disease: are we there yet?

Sickle cell disease (SCD, OMIM #603903), an autosomal recessively inherited β-hemoglobinopathy, was the first human disorder delineated at a molecular level. The putative single nucleotide mutation in the HBB gene generates an abnormal hemoglobin species, which polymerizes in deoxygenated conditions causing irreversible changes in erythrocyte shape and function. Sickling erythrocytes are in turn responsible for microvascular vaso-occlusion, hemolysis and a systemic vasculopathy in patients. SCD has represented an attractive field for proteomic investigation since its methodological infancy. Clinically actionable biomarkers, especially for the prevention of cerebrovascular complications in children with the condition, are urgently needed and their discovery remains a major challenge. In this issue, Lance and colleagues report of their unbiased proteomic studies on samples from the participants of the landmark prospective, randomized, single-blind SIT trial (NEJM 2014). Their results reveal numerous brain-enriched plasma proteins specific for SCD, and for silent cerebral infarcts in this disorder, and further analyses highlight novel cellular mechanisms behind the brain damage in SCD. Although the goal of identifying reliable biomarker candidates for cerebrovascular complications could not be met, the dataset produced by the authors constitutes a significant contribution to the field and opens new horizons for further clinical and laboratory investigation.

LIN28B Underlies the Pathogenesis of a Subclass of Ewing Sarcoma LIN28B Control of EWS-FLI1 Stability

Ewing sarcoma (EwS) is associated with poor prognosis despite current multimodal therapy. Targeting of EWS-FLI1, the fusion protein responsible for its pathogenesis, and its principal downstream targets has not yet produced satisfactory therapeutic options, fueling the search for alternative approaches. Here, we show that the oncofetal RNA-binding protein LIN28B regulates the stability of EWS-FLI1 mRNA in ~10% of EwSs. LIN28B depletion in these tumors leads to a decrease in the expression of EWS-FLI1 and its direct transcriptional network, abrogating EwS cell self-renewal and tumorigenicity. Moreover, pharmacological inhibition of LIN28B mimics the effect of LIN28B depletion, suggesting that LIN28B sustains the emergence of a subset of EwS in which it also serves as an effective therapeutic target.

Immune deficiency, autoimmune disease and intellectual disability: A pleiotropic disorder caused by biallelic variants in the TPP2 gene

Four individuals from two families presented with a multisystemic condition of suspected genetic origin that was diagnosed only after genome analysis. The main phenotypic features were immune system dysregulation (severe immunodeficiency with autoimmunity) and intellectual disability. The four individuals were found to be homozygous for a 4.4 Kb deletion removing exons 20-23 (NM_003291.4) of the TPP2 gene, predicting a frameshift with premature termination of the protein. The deletion was located on a shared chromosome 13 haplotype indicating a Swiss founder mutation. Tripeptidyl peptidase 2 (TPP2) is a protease involved in HLA/antigen complex processing and amino acid homeostasis. Biallelic variants in TPP2 have been described in 10 individuals with variable features including immune deficiency, autoimmune cytopenias, and intellectual disability or chronic sterile brain inflammation mimicking multiple sclerosis. Our observations further delineate this severe condition not yet included in the OMIM catalog. Timely recognition of TPP2 deficiency is crucial since (1) immune surveillance is needed and hematopoietic stem cell transplantation may be necessary, and (2) for provision of genetic counselling. Additionally, enzyme replacement therapy, as already established for TPP1 deficiency, might be an option in the future.

Cancer Care of Children, Adolescents and Adults With Autism Spectrum Disorders: Key Information and Strategies for Oncology Teams

Delivering optimal cancer care to children, adolescents and adults with ASD has recently become a healthcare priority and represents a major challenge for all providers involved. In this review, and after consideration of the available evidence, we concisely deliver key information on this heterogenous group of neurodevelopmental disorders, as well as recommendations and concrete tools for the enhanced oncological care of this vulnerable population of patients.

Pediatric cranial osteoblastoma: Technical note of surgical treatment and review of the literature

Osteoblastoma of the skull is a rare entity, and they account only for 2-4% of all the cases of osteoblastoma. We perform a comprehensive review of the pertinent literature on the subject and we report a case of a 3-year-old girl presenting with a 6-month history of a supraorbital mass and exophthalmos due to an osteoblastoma of the frontal and ethmoid bones involving the orbit and anterior skull base. A 3D printed model of the patient's skull was used for the preoperative planning and reconstruction strategy. Total en-bloc resection of the tumor followed by immediate reconstruction was achieved. No recurrence was detected 3 years after the surgery. Gross total resection is strongly advised with skull osteoblastoma, especially in young age, because of the risk of the recurrence and malignant transformation. 3D printing is proven to be a valuable tool to enhance surgical performance by avoiding complications while achieving total resection with accurate reconstruction. Long-term follow-up is important to detect recurrences and improve the management of these young patients.

Parental occupational exposure to pesticides and risk of childhood cancer in Switzerland: a census-based cohort study

BACKGROUND

Pesticide exposure is a suspected risk factor for childhood cancer. We investigated the risk of developing childhood cancer in relation to parental occupational exposure to pesticides in Switzerland for the period 1990-2015.

METHODS

From a nationwide census-based cohort study in Switzerland, we included children aged < 16 years at national censuses of 1990 and 2000 and followed them until 2015. We extracted parental occupations reported at the census closest to the birth year of the child and estimated exposure to pesticides using a job exposure matrix. Cox proportional hazards models, adjusted for potential confounders, were fitted for the following outcomes: any cancer, leukaemia, central nervous system tumours (CNST), lymphoma, non-CNS solid tumours.

RESULTS

Analyses of maternal (paternal) exposure were based on approximately 15.9 (15.1) million-person years at risk and included 1891 (1808) cases of cancer, of which 532 (503) were leukaemia, 348 (337) lymphomas, 423 (399) CNST, and 588 (569) non-CNS solid tumours. The prevalence of high likelihood of exposure was 2.9% for mothers and 6.7% for fathers. No evidence of an association was found with maternal or paternal exposure for any of the outcomes, except for "non-CNS solid tumours" (High versus None; Father: adjusted HR [95%CI] =1.84 [1.31-2.58]; Mother: 1.79 [1.13-2.84]). No evidence of an association was found for main subtypes of leukaemia and lymphoma. A post-hoc analysis on frequent subtypes of "non-CNS solid tumours" showed positive associations with wide CIs for some cancers.

CONCLUSION

Our study suggests an increased risk for solid tumours other than in the CNS among children whose parents were occupationally exposed to pesticides; however, the small numbers of cases limited a closer investigation of cancer subtypes. Better exposure assessment and pooled studies are needed to further explore a possible link between specific childhood cancers types and parental occupational exposure to pesticides.

Genetic and functional insights into CDA-I prevalence and pathogenesis

BACKGROUND

Congenital dyserythropoietic anaemia type I (CDA-I) is a hereditary anaemia caused by biallelic mutations in the widely expressed genes CDAN1 and C15orf41. Little is understood about either protein and it is unclear in which cellular pathways they participate.

METHODS

Genetic analysis of a cohort of patients with CDA-I identifies novel pathogenic variants in both known causative genes. We analyse the mutation distribution and the predicted structural positioning of amino acids affected in Codanin-1, the protein encoded by CDAN1. Using western blotting, immunoprecipitation and immunofluorescence, we determine the effect of particular mutations on both proteins and interrogate protein interaction, stability and subcellular localisation.

RESULTS

We identify six novel CDAN1 mutations and one novel mutation in C15orf41 and uncover evidence of further genetic heterogeneity in CDA-I. Additionally, population genetics suggests that CDA-I is more common than currently predicted. Mutations are enriched in six clusters in Codanin-1 and tend to affect buried residues. Many missense and in-frame mutations do not destabilise the entire protein. Rather C15orf41 relies on Codanin-1 for stability and both proteins, which are enriched in the nucleolus, interact to form an obligate complex in cells.

CONCLUSION

Stability and interaction data suggest that C15orf41 may be the key determinant of CDA-I and offer insight into the mechanism underlying this disease. Both proteins share a common pathway likely to be present in a wide variety of cell types; however, nucleolar enrichment may provide a clue as to the erythroid specific nature of CDA-I. The surprisingly high predicted incidence of CDA-I suggests that better ascertainment would lead to improved patient care.

Diagnosis and management of iron deficiency in children with or without anemia: consensus recommendations of the SPOG Pediatric Hematology Working Group

Iron deficiency is the most prevalent nutritional deficiency affecting children and adolescents worldwide. A consistent body of epidemiological data demonstrates an increased incidence of iron deficiency at three timepoints: in the neonatal period, in preschool children, and in adolescents, where it particularly affects females.Conclusion: This narrative review focuses on the most suggestive symptoms of iron deficiency in childhood, describes the diagnostic procedures in situations with or without anemia, and provides Swiss expert-based management recommendations for the pediatric context.What is Known:• Iron deficiency (ID) is one of the most common challenges faced by pediatricians.• Significant progress in the diagnosis and therapy of ID has been made over the last decade.What is New:• Our expert panel provides ID management recommendations based on the best available evidence.• They include strategies for ID diagnosis and therapy, both oral and intravenous.

Perioperative care of children with sickle cell disease: A systematic review and clinical recommendations

Children with sickle cell disease (SCD) require specific perioperative care, and clinical practice in this area remains poorly defined. We aimed to conduct a systematic, PRISMA-based review of the literature, available clinical guidelines and practice recommendations. We also aimed to extract any valuable information for the "best of available-evidence"-based prevention of perioperative adverse events in children with SCD, and highlight the most urgent priorities in clinical research. As data sources, US National Library of Medicine, Medline, National Guideline Clearinghouse, International Guideline Network, TRIP databases were searched for any content until January 2019. We also included institutional, consortia and expert group guidelines. Included were reports/guidelines in English, French, German, and Italian. Excluded were reports on obstetrical and fetal management. We identified 202 reports/guidelines fulfilling the criteria outlined above. A majority focused on visceral, cardiovascular and orthopedic surgery procedures, and only five were multicenter randomized controlled trials and two prospective randomized studies. After grading of the quality of the evidence, the extracted data was summarized into clinical recommendations for daily practice. Additionally, we designed a risk-grading algorithm to identify contexts likely to be associated with adverse outcomes. In conclusion, we provide a systematic PRISMA-based review of the existing literature and ancillary practice and delineate a set of clinical recommendations and priorities for research.

Expression of the Neuroblastoma-Associated ALK-F1174L Activating Mutation During Embryogenesis Impairs the Differentiation of Neural Crest Progenitors in Sympathetic Ganglia

Neuroblastoma (NB) is an embryonal malignancy derived from the abnormal differentiation of the sympathetic nervous system. The Anaplastic Lymphoma Kinase (ALK) gene is frequently altered in NB, through copy number alterations and activating mutations, and represents a predisposition in NB-genesis when mutated. Our previously published data suggested that ALK activating mutations may impair the differentiation potential of neural crest (NC) progenitor cells. Here, we demonstrated that the expression of the endogenous ALK gene starts at E10.5 in the developing sympathetic ganglia (SG). To decipher the impact of deregulated ALK signaling during embryogenesis on the formation and differentiation of sympathetic neuroblasts, Sox10-Cre;LSL-ALK-F1174L embryos were produced to restrict the expression of the human ALK-F1174L transgene to migrating NC cells (NCCs). First, ALK-F1174L mediated an embryonic lethality at mid-gestation and an enlargement of SG with a disorganized architecture in Sox10-Cre;LSL-ALK-F1174L embryos at E10.5 and E11.5. Second, early sympathetic differentiation was severely impaired in Sox10-Cre;LSL-ALK-F1174L embryos. Indeed, their SG displayed a marked increase in the proportion of NCCs and a decrease of sympathetic neuroblasts at both embryonic stages. Third, neuronal and noradrenergic differentiations were blocked in Sox10-Cre;LSL-ALK-F1174L SG, as a reduced proportion of Phox2b⁺ sympathoblasts expressed βIII-tubulin and almost none were Tyrosine Hydroxylase (TH) positive. Finally, at E10.5, ALK-F1174L mediated an important increase in the proliferation of Phox2b⁺ progenitors, affecting the transient cell cycle exit observed in normal SG at this embryonic stage. Altogether, we report for the first time that the expression of the human ALK-F1174L mutation in NCCs during embryonic development profoundly disturbs early sympathetic progenitor differentiation, in addition to increasing their proliferation, both mechanisms being potential crucial events in NB oncogenesis.

[Iron deficiency with and without anemia in children: a brief update for caregivers]

Non anemic iron deficiency (NAID) is the most common nutritional deficiency. Symptoms more frequently observed in children and adolescents include fatigue, delayed psychomotor development as well as decreased school and athletic performances. Iron treatment is effective in improving symptoms in older children and adolescents. In children under 2 years of age, there is currently no evidence of the efficacy of substitution therapy on development. Preemptive treatment is not justified considering the available evidence beyond premature or small newborns for gestational age and should only be initiated if a diagnosis of iron deficiency is confirmed. Oral iron supplementation is the first-line treatment of NAID.

[Recent advances and future directions in CAR-T cell therapy in pediatric oncology]

Fighting leukemia using the immune system (antibodies, lymphocytes) is an old idea, which has already been fulfilled in allogeneic bone marrow transplantation. Indeed, the effectiveness of the transplant depends on the action of the donor lymphocytes. To limit the adverse effects on bystander organs (graft-versus-host disease), autologous T cells can be engineered to express synthetic chimeric antigen receptors (CARs) with artificially redirected antigen specificity. Autologous T cells engineered to express a CAR targeting CD19 have shown unprecedented efficacy in clinical trials for relapsed/refractory B-cell leukemias and lymphomas. In this review article, we describe the therapeutic strategies, clinical trial results, side effects and future direction of CAR T cell therapy in B cell acute lymphoblastic leukemia and other pediatric cancers and its future role in the Swiss setting.

A key role for Rac and Pak signaling in neutrophil extracellular traps (NETs) formation defines a new potential therapeutic target

NET formation in mice (NETosis) is supported by reactive oxygen species (ROS) production by NADPH oxidase and histone hypercitrullination by peptidylarginine deiminase 4 (PAD4). Rac1 and Rac2, expressed in polymorphonuclear neutrophils (PMNs), regulate the cytoskeleton, cell shape, adhesion, and migration and are also essential components of the NADPH oxidase complex. We aimed to explore the role of the Rac signaling pathway including the upstream guanosine exchange factor (GEF) activator, Vav, and a downstream effector, the p21-activated kinase, Pak, on NETosis in PMNs using a previously described flow-cytometry-based assay. Rac2^-/- PMNs showed reduced levels of citrullinated histone H3 (H3Cit)-positive cells and defective NETosis. Rac1^Δ/Δ ; Rac2^-/- PMNs demonstrated a further reduction in PMA-induced H3Cit levels and a more profound impairment of NETosis than deletion of Rac2 alone, suggesting an overlapping role of these two highly related proteins. Genetic knockouts of Vav1, or Vav2, did not impair H3Cit response to phorbol myristate ester (PMA) or NETosis. Combined, Vav1 and Vav3 deletions decreased H3Cit response and caused a modest but significant impairment of NETosis. Pharmacologic inhibition of Pak by two inhibitors with distinct mechanisms of action, led to reduced H3Cit levels after PMA stimulation, as well as significant inhibition of NETosis. We validated the importance of Pak using Pak2^Δ/Δ PMNs, which demonstrated significantly impaired histone H3 citrullination and NETosis. These data confirm and more comprehensively define the key role of the Rac signaling pathway in PMN NETosis. The Rac signaling cascade may represent a valuable target for inhibition of NETosis and related pathological processes.

Opportunities and challenges in the immunological therapy of pediatric malignancy: a concise snapshot

Over the last 50 years, collaborative clinical trials have reduced the number of children dying from pediatric cancer significantly. Unfortunately, certain tumor types have remained resistant to conventional surgical, radiotherapy and chemotherapy combinations, and relapsing and/or refractory disease remains associated with dismal outcomes. Recently, renewed attention has been given to the role for immunotherapies in pediatric oncology. In fact, these combine several attractive features, including (but possibly not limited to) the specificity for cancer cells, potentially in vivo persistence and longevity, and potency against refractory disease. In this narrative review designed for the academic pediatrician, we will concisely review the biological underpinnings behind the immunological therapy of pediatric neoplasms and illustrate the current humoral, cellular approaches, and novel drugs targeting the immune checkpoint, oncolytic viruses, and tumor vaccines. We will also comment on the future directions, challenges, and open questions faced by the field. What is Known: • Cancer immunotherapy drives immune cells and its humoral weaponry to eliminate tumor cells. • This occurs by recognizing antigens ideally expressed only on tumoral, but not normal/healthy, cells. What is New: • Clinical immunotherapy trials have shown responses in children with relapsing/refractory neoplasms. • Novel humoral/cellular immunotherapies, immune checkpoint inhibitors, oncolytic viruses, and tumor vaccines are currently being investigated in pediatric oncology.

Aldehyde dehydrogenase activity plays a Key role in the aggressive phenotype of neuroblastoma

BACKGROUND

The successful targeting of neuroblastoma (NB) by associating tumor-initiating cells (TICs) is a major challenge in the development of new therapeutic strategies. The subfamily of aldehyde dehydrogenases 1 (ALDH1) isoenzymes, which comprises ALDH1A1, ALDH1A2, and ALDH1A3, is involved in the synthesis of retinoic acid, and has been identified as functional stem cell markers in diverse cancers. By combining serial neurosphere passages with gene expression profiling, we have previously identified ALDH1A2 and ALDH1A3 as potential NB TICs markers in patient-derived xenograft tumors. In this study, we explored the involvement of ALDH1 isoenzymes and the related ALDH activity in NB aggressive properties.

METHODS

ALDH activity and ALDH1A1/A2/A3 expression levels were measured using the ALDEFLUOR™ kit, and by real-time PCR, respectively. ALDH activity was inhibited using the specific ALDH inhibitor diethylaminobenzaldehyde (DEAB), and ALDH1A3 gene knock-out was generated through the CRISPR/Cas9 technology.

RESULTS

We first confirmed the enrichment of ALDH1A2 and ALDH1A3 mRNA expression in NB cell lines and patient-derived xenograft tumors during neurosphere passages. We found that high ALDH1A1 expression was associated with less aggressive NB tumors and cell lines, and correlated with favorable prognostic factors. In contrast, we observed that ALDH1A3 was more widely expressed in NB cell lines and was associated with poor survival and high-risk prognostic factors. We also identified an important ALDH activity in various NB cell lines and patient-derived xenograft tumors. Specific inhibition of ALDH activity with diethylaminobenzaldehyde (DEAB) resulted in a strong reduction of NB cell clonogenicity, and TIC self-renewal potential, and partially enhanced NB cells sensitivity to 4-hydroxycyclophosphamide. Finally, the specific knock-out of ALDH1A3 via CRISPR/Cas9 gene editing reduced NB cell clonogenicity, and mediated a cell type-dependent inhibition of TIC self-renewal properties.

CONCLUSIONS

Together our data uncover the participation of ALDH enzymatic activity in the aggressive properties and 4-hydroxycyclophosphamide resistance of NB, and show that the specific ALDH1A3 isoenzyme increases the aggressive capacities of a subset of NB cells.

Lineage-specific BCL11A knockdown circumvents toxicities and reverses sickle phenotype

Reducing expression of the fetal hemoglobin (HbF) repressor BCL11A leads to a simultaneous increase in γ-globin expression and reduction in β-globin expression. Thus, there is interest in targeting BCL11A as a treatment for β-hemoglobinopathies, including sickle cell disease (SCD) and β-thalassemia. Here, we found that using optimized shRNAs embedded within an miRNA (shRNAmiR) architecture to achieve ubiquitous knockdown of BCL11A profoundly impaired long-term engraftment of both human and mouse hematopoietic stem cells (HSCs) despite a reduction in nonspecific cellular toxicities. BCL11A knockdown was associated with a substantial increase in S/G2-phase human HSCs after engraftment into immunodeficient (NSG) mice, a phenotype that is associated with HSC exhaustion. Lineage-specific, shRNAmiR-mediated suppression of BCL11A in erythroid cells led to stable long-term engraftment of gene-modified cells. Transduced primary normal or SCD human HSCs expressing the lineage-specific BCL11A shRNAmiR gave rise to erythroid cells with up to 90% reduction of BCL11A protein. These erythrocytes demonstrated 60%-70% γ-chain expression (vs. < 10% for negative control) and a corresponding increase in HbF. Transplantation of gene-modified murine HSCs from Berkeley sickle cell mice led to a substantial improvement of sickle-associated hemolytic anemia and reticulocytosis, key pathophysiological biomarkers of SCD. These data form the basis for a clinical trial application for treating sickle cell disease.

Mathematical modeling of erythrocyte chimerism informs genetic intervention strategies for sickle cell disease

Recent advances in gene therapy and genome-engineering technologies offer the opportunity to correct sickle cell disease (SCD), a heritable disorder caused by a point mutation in the β-globin gene. The developmental switch from fetal γ-globin to adult β-globin is governed in part by the transcription factor (TF) BCL11A. This TF has been proposed as a therapeutic target for reactivation of γ-globin and concomitant reduction of β-sickle globin. In this and other approaches, genetic alteration of a portion of the hematopoietic stem cell (HSC) compartment leads to a mixture of sickling and corrected red blood cells (RBCs) in periphery. To reverse the sickling phenotype, a certain proportion of corrected RBCs is necessary; the degree of HSC alteration required to achieve a desired fraction of corrected RBCs remains unknown. To address this issue, we developed a mathematical model describing aging and survival of sickle-susceptible and normal RBCs; the former can have a selective survival advantage leading to their overrepresentation. We identified the level of bone marrow chimerism required for successful stem cell-based gene therapies in SCD. Our findings were further informed using an experimental mouse model, where we transplanted mixtures of Berkeley SCD and normal murine bone marrow cells to establish chimeric grafts in murine hosts. Our integrative theoretical and experimental approach identifies the target frequency of HSC alterations required for effective treatment of sickling syndromes in humans. Our work replaces episodic observations of such target frequencies with a mathematical modeling framework that covers a large and continuous spectrum of chimerism conditions. Am. J. Hematol. 91:931-937, 2016. © 2016 Wiley Periodicals, Inc.

Flow cytometric assay for direct quantification of neutrophil extracellular traps in blood samples

Neutrophil extracellular traps (NETs) contribute to innate immunity as well as numerous diseases processes such as deep vein thrombosis, myocardial ischemia, and autoimmune disease. To date, most knowledge on NETs formation has been gathered via the qualitative microscopic examination of individual neutrophils in vitro, or aggregate structures in vivo. Here we describe a novel flow cytometry (FLOW)-based assay to identify and quantify NETs using antibodies against key NETs constituents, specifically DNA, modified histones, and granular enzymes. This method is applicable to both murine and human samples for the assessment of induced NETs in vitro, or detection of NETosis in vivo in blood samples. This FLOW-based method was validated by comparison with the well-established microscopy assay using two genetic mouse models previously demonstrated to show defective NETosis. It was then used on healthy human neutrophils for detection of ex vivo induced NETs and on blood samples from patients with sepsis for direct assessment of in vivo NET-forming neutrophils. This new methodology allows rapid and robust assessment of several thousand cells per sample and is independent of potential observer-bias, the two main limitations of the microscopic quantification. Using this new technology facilitates the direct detection of in vivo circulating NETs in blood samples and purification of NETting neutrophils by fluorescence-activated cell sorting (FACS) for further analysis.

miRNA-embedded shRNAs for Lineage-specific BCL11A Knockdown and Hemoglobin F Induction

RNA interference (RNAi) technology using short hairpin RNAs (shRNAs) expressed via RNA polymerase (pol) III promoters has been widely exploited to modulate gene expression in a variety of mammalian cell types. For certain applications, such as lineage-specific knockdown, embedding targeting sequences into pol II-driven microRNA (miRNA) architecture is required. Here, using the potential therapeutic target BCL11A, we demonstrate that pol III-driven shRNAs lead to significantly increased knockdown but also increased cytotoxcity in comparison to pol II-driven miRNA adapted shRNAs (shRNA(miR)) in multiple hematopoietic cell lines. We show that the two expression systems yield mature guide strand sequences that differ by a 4 bp shift. This results in alternate seed sequences and consequently influences the efficacy of target gene knockdown. Incorporating a corresponding 4 bp shift into the guide strand of shRNA(miR)s resulted in improved knockdown efficiency of BCL11A. This was associated with a significant de-repression of the hemoglobin target of BCL11A, human γ-globin or the murine homolog Hbb-y. Our results suggest the requirement for optimization of shRNA sequences upon incorporation into a miRNA backbone. These findings have important implications in future design of shRNA(miR)s for RNAi-based therapy in hemoglobinopathies and other diseases requiring lineage-specific expression of gene silencing sequences.

Exploring the association of succinate dehydrogenase complex mutations with lymphoid malignancies

The succinate dehydrogenase (SDH) complex exerts a fundamental role in mitochondrial cellular respiration and mutations in its encoding genes (SDHA, SDHB, SDHC, SDHD, collectively referred to as SDHx) lead to a number of inherited endocrine cancer predisposition syndromes, including familial paraganglioma/pheochromocytoma. Recent studies suggest a possible role for the SDH complex and other mitochondrial enzymes in the pathogenesis of hematological malignancy. Our aim was to search and identify pedigrees of patients affected by germline SHDx mutations treated at our institution for endocrine and other tumors, and seek to identify cases of hematological malignancy. We also analyzed cancer genome databases for reported cases of SDHx mutations outside of endocrine neoplasms. We report of two unrelated pedigrees carrying SDHx mutations with members affected by lymphomas. Sequencing data revealed one case of chronic lymphocytic leukemia with a SDHB mutation. This novel set of observations demonstrates the need for collaborative databases of patients with endocrine cancers with SDHx mutations, and the investigation of their role in hematological (lymphoid) malignancy.

Genetic deletion of the GATA1-regulated protein α-synuclein reduces oxidative stress and nitric oxide synthase levels in mature erythrocytes

α-Synuclein is highly expressed in neural tissue and during erythropoiesis, where the key erythroid regulator GATA1 has been found to modulate its expression. While specific α-synuclein (SNCA) mutations are known to cause autosomal dominant familial Parkinson's disease, its wild-type function remains under debate. To investigate the role of α-synuclein in murine hematopoiesis and erythropoiesis, we utilized Snca knock-out mice and analyzed erythroid compartments for maturation defects, in vivo erythrocyte survival, and erythrocyte-based reactive oxygen species (ROS) and nitric oxide synthase (NOS) levels. Our findings show that while bone marrow and spleen erythropoiesis and peripheral blood erythrocyte survival in Snca(-/-) mice was comparable to controls, the levels of ROS and of NOS-2 were significantly decreased in mature erythrocytes in these animals. These results indicate a role for α-synuclein in regulating oxidative stress in erythrocytes in vivo and could open new avenues for the investigation of its function in non-neural tissue.

Generation of bivalent chromatin domains during cell fate decisions

Background

In self-renewing, pluripotent cells, bivalent chromatin modification is thought to silence (H3K27me3) lineage control genes while 'poising' (H3K4me3) them for subsequent activation during differentiation, implying an important role for epigenetic modification in directing cell fate decisions. However, rather than representing an equivalently balanced epigenetic mark, the patterns and levels of histone modifications at bivalent genes can vary widely and the criteria for identifying this chromatin signature are poorly defined.

Results

Here, we initially show how chromatin status alters during lineage commitment and differentiation at a single well characterised bivalent locus. In addition we have determined how chromatin modifications at this locus change with gene expression in both ensemble and single cell analyses. We also show, on a global scale, how mRNA expression may be reflected in the ratio of H3K4me3/H3K27me3.

Conclusions

While truly 'poised' bivalently modified genes may exist, the original hypothesis that all bivalent genes are epigenetically premarked for subsequent expression might be oversimplistic. In fact, from the data presented in the present work, it is equally possible that many genes that appear to be bivalent in pluripotent and multipotent cells may simply be stochastically expressed at low levels in the process of multilineage priming. Although both situations could be considered to be forms of 'poising', the underlying mechanisms and the associated implications are clearly different.