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The linear chromosome of the bacterium Streptomyces exhibits a remarkable genetic organization with grossly a central conserved region flanked by variable chromosomal arms. The terminal diversity co-locates with an intense DNA plasticity including the occurrence of large deletions associated to circularization and chromosomal arm exchange. These observations prompted us to assess the role of double strand break (DSB) repair in chromosome plasticity following. For that purpose, DSBs were induced along the chromosome using the meganuclease I- Sce I. DSB repair in the central region of the chromosome was mutagenic at the healing site but kept intact the whole genome structure. In contrast, DSB repair in the chromosomal arms was mostly associated to the loss of the targeted chromosomal arm and extensive deletions beyond the cleavage sites. While homologous recombination occurring between copies of DNA sequences accounted for the most part of the chromosome rescue events, Non Homologous End Joining was involved in mutagenic repair as well as in huge genome rearrangements (i.e. circularization). Further, NHEJ repair was concomitant with the integration of genetic material at the healing site. We postulate that DSB repair drives genome plasticity and evolution in Streptomyces and that NHEJ may foster horizontal transfer in the environment.

The individual response to ionizing radiation (IR) raises a number of medical, scientific, and societal issues. While the term “radiosensitivity” was used by the pioneers at the beginning of the 20st century to describe only the radiation-induced adverse tissue reactions related to cell death, a confusion emerged in the literature from the 1930s, as “radiosensitivity” was indifferently used to describe the toxic, cancerous, or aging effect of IR. In parallel, the predisposition to radiation-induced adverse tissue reactions (radiosensitivity), notably observed after radiotherapy appears to be caused by different mechanisms than those linked to predisposition to radiation-induced cancer (radiosusceptibility). This review aims to document these differences in order to better estimate the different radiation-induced risks. It reveals that there are very few syndromes associated with the loss of biological functions involved directly in DNA damage recognition and repair as their role is absolutely necessary for cell viability. By contrast, some cytoplasmic proteins whose functions are independent of genome surveillance may also act as phosphorylation substrates of the ATM protein to regulate the molecular response to IR. The role of the ATM protein may help classify the genetic syndromes associated with radiosensitivity and/or radiosusceptibility.

There is a constant need for new and improved drugs to combat infectious diseases, cancer, and other major life-threatening conditions. The recent development of genomics-guided approaches for novel natural product discovery has stimulated renewed interest in the search for natural product-based drugs. Genome sequence analysis of Streptomyces ambofaciens ATCC23877 has revealed numerous secondary metabolite biosynthetic gene clusters, including a giant type I modular polyketide synthase (PKS) gene cluster, which is composed of 25 genes (nine of which encode PKSs) and spans almost 150 kb, making it one of the largest polyketide biosynthetic gene clusters described to date. The metabolic product(s) of this gene cluster are unknown, and transcriptional analyses showed that it is not expressed under laboratory growth conditions. The constitutive expression of a regulatory gene within the cluster, encoding a protein that is similar to Large ATP binding of the LuxR (LAL) family proteins, triggered the expression of the biosynthetic genes. This led to the identification of four 51-membered glycosylated macrolides, named stambomycins A-D as metabolic products of the gene cluster. The structures of these compounds imply several interesting biosynthetic features, including incorporation of unusual extender units into the polyketide chain and in trans hydroxylation of the growing polyketide chain to provide the hydroxyl group for macrolide formation. Interestingly, the stambomycins possess promising antiproliferative activity against human cancer cell lines. Database searches identify genes encoding LAL regulators within numerous cryptic biosynthetic gene clusters in actinomycete genomes, suggesting that constitutive expression of such pathway-specific activators represents a powerful approach for novel bioactive natural product discovery.

Background Pediatric diffuse intrinsic pontine glioma (DIPG) represents one of the most devastating and lethal brain tumors in children with a median survival of 12 months. The high mortality rate can be explained by the ineligibility of patients to surgical resection due to the diffuse growth pattern and midline localization of the tumor. While the therapeutic strategies are unfortunately palliative, the blood–brain barrier (BBB) is suspected to be responsible for the treatment inefficiency. Located at the brain capillary endothelial cells (ECs), the BBB has specific properties to tightly control and restrict the access of molecules to the brain parenchyma including chemotherapeutic compounds. However, these BBB specific properties can be modified in a pathological environment, thus modulating brain exposure to therapeutic drugs. Hence, this study aimed at developing a syngeneic human blood–brain tumor barrier model to understand how the presence of DIPG impacts the structure and function of brain capillary ECs. Methods A human syngeneic in vitro BBB model consisting of a triple culture of human (ECs) (differentiated from CD34 + -stem cells), pericytes and astrocytes was developed. Once validated in terms of BBB phenotype, this model was adapted to develop a blood–brain tumor barrier (BBTB) model specific to pediatric DIPG by replacing the astrocytes by DIPG-007, -013 and -014 cells. The physical and metabolic properties of the BBTB ECs were analyzed and compared to the BBB ECs. The permeability of both models to chemotherapeutic compounds was evaluated. Results In line with clinical observation, the integrity of the BBTB ECs remained intact until 7 days of incubation. Both transcriptional expression and activity of efflux transporters were not strongly modified by the presence of DIPG. The permeability of ECs to the chemotherapeutic drugs temozolomide and panobinostat was not affected by the DIPG environment. Conclusions This original human BBTB model allows a better understanding of the influence of DIPG on the BBTB ECs phenotype. Our data reveal that the chemoresistance described for DIPG does not come from the development of a “super BBB”. These results, validated by the absence of modification of drug transport through the BBTB ECs, point out the importance of understanding the implication of the different protagonists in the pathology to have a chance to significantly improve treatment efficiency.

Pediatric high-grade gliomas (pHGGs) are a deadly and heterogenous subgroup of gliomas for which the development of innovative treatments is urgent. Advances in high-throughput molecular techniques have shed light on key epigenetic components of these diseases, such as K27M and G34R/V mutations on histone 3. However, modification of DNA compaction is not sufficient by itself to drive those tumors. Here, we review molecular specificities of pHGGs subcategories in the context of epigenomic rewiring caused by H3 mutations and the subsequent oncogenic interplay with transcriptional signaling pathways co-opted from developmental programs that ultimately leads to gliomagenesis. Understanding how transcriptional and epigenetic alterations synergize in each cellular context in these tumors could allow the identification of new Achilles’ heels, thereby highlighting new levers to improve their therapeutic management.

ABSTRACT Background Pediatric low‐grade gliomas are common brain tumors often driven by MAPK pathway alterations, including rare BRAF mutations. Case This case report describes the first use of treatment combining dabrafenib and trametinib in a 10‐year‐old boy with pleomorphic xanthoastrocytoma harboring a BRAF A598_(T)599insI mutation. Surgery and chemotherapy failed, leading to metastatic progression; yet targeted therapy has achieved a sustained clinical and radiological response, lasting more than 2 years. Conclusion This case highlights the potential of RAF/MEK inhibitors in rare BRAF‐mutated tumors and underscores the need for research to optimize treatment duration, manage side effects, and explore their role in non‐canonical mutations.

In this work, by comparing genomes of closely related individuals of Streptomyces isolated at a spatial microscale (millimeters or centimeters), we investigated the extent and impact of horizontal gene transfer in the diversification of a natural Streptomyces population. We show that despite these conspecific strains sharing a recent common ancestor, all harbored significantly different gene contents , implying massive and rapid gene flux. The accessory genome of the strains was distributed across insertion/deletion events (indels) ranging from one to several hundreds of genes. Indels were preferentially located in the arms of the linear chromosomes (ca. 12 Mb) and appeared to form recombination hot spots. Some of them harbored biosynthetic gene clusters (BGCs) whose products confer an inhibitory capacity and may constitute public goods that can favor the cohesiveness of the bacterial population. Moreover, a significant proportion of these variable genes were either plasmid borne or harbored signatures of actinomycete integrative and conjugative elements (AICEs). We propose that conjugation is the main driver for the indel flux and diversity in Streptomyces populations. IMPORTANCE Horizontal gene transfer is a rapid and efficient way to diversify bacterial gene pools. Currently, little is known about this gene flux within natural soil populations. Using comparative genomics of Streptomyces strains belonging to the same species and isolated at microscale, we reveal frequent transfer of a significant fraction of the pangenome. We show that it occurs at a time scale enabling the population to diversify and to cope with its changing environment, notably, through the production of public goods.

In terms of overall survival (OS), limited data are available for the very long-term outcomes of children treated for optic pathway glioma (OPG) with up-front chemotherapy. Therefore, we undertook this study with the aim of clarifying long-term OS and causes of death in these patients. We initiated and analyzed a historical cohort study of 180 children with OPG treated in France with BB-SFOP chemotherapy between 1990 and 2004. The survival distributions were estimated using Kaplan-Meier method. The effect of potential risk factors on the risk of death was described using Cox regression analysis. The OS was 95% [95% CI: 90.6-97.3] 5 years after diagnosis and significantly decreased over time without ever stabilizing: 91.6% at 10 years [95% CI: 86.5-94.8], 80.7% at 15 years [95% CI: 72.7-86.8] and 75.5% [95% CI: 65.6-83] at 18 years. Tumor progression was the most common cause of death (65%). Age and intracranial hypertension at diagnosis were significantly associated with a worse prognosis. Risk of death was increased by 3.1[95% CI: 1.5-6.2] (p=0.002) for patients less than 1 year old at diagnosis and by 5.2[95% CI: 1.5-17.6] (p=0.007) for patients with initial intracranial hypertension. Boys without diencephalic syndrome had a better prognosis (HR: 0.3 [95% CI: 0.1-0.8], p=0.007). This study shows that i) in children with OPG, OS is not as favorable as previously described and ii) patients can be classified into 2 groups depending on risk factors (age, intracranial hypertension, sex and diencephalic syndrome) with an OS rate of 50.4% at 18 years [95% CI: 31.4-66.6] in children with the worst prognosis. These findings could justify, depending on the initial risk, a different therapeutic approach to this tumor with more aggressive treatment (especially chemotherapy) in patients with high risk factors.

The phosphopantetheinyl transferases (PPTases) are responsible for the activation of the carrier protein domains of the polyketide synthases (PKS), non ribosomal peptide synthases (NRPS) and fatty acid synthases (FAS). The analysis of the Streptomyces ambofaciens ATCC23877 genome has revealed the presence of four putative PPTase encoding genes. One of these genes appears to be essential and is likely involved in fatty acid biosynthesis. Two other PPTase genes, samT0172 (alpN) and samL0372, are located within a type II PKS gene cluster responsible for the kinamycin production and an hybrid NRPS-PKS cluster involved in antimycin production, respectively, and their products were shown to be specifically involved in the biosynthesis of these secondary metabolites. Surprisingly, the fourth PPTase gene, which is not located within a secondary metabolite gene cluster, appears to play a pleiotropic role. Its product is likely involved in the activation of the acyl- and peptidyl-carrier protein domains within all the other PKS and NRPS complexes encoded by S. ambofaciens. Indeed, the deletion of this gene affects the production of the spiramycin and stambomycin macrolide antibiotics and of the grey spore pigment, all three being PKS-derived metabolites, as well as the production of the nonribosomally produced compounds, the hydroxamate siderophore coelichelin and the pyrrolamide antibiotic congocidine. In addition, this PPTase seems to act in concert with the product of samL0372 to activate the ACP and/or PCP domains of the antimycin biosynthesis cluster which is also responsible for the production of volatile lactones.

The bacteria of the genus Streptomyces and Basidiomycete fungi harbor many biosynthetic gene clusters (BGCs) that are at the origin of many bioactive molecules with medical or industrial interests. Nevertheless, most BGCs do not express in standard lab growth conditions, preventing the full metabolic potential of these organisms from being exploited. Because it generates biotic cues encountered during natural growth conditions, co-culture is a means to elicit such cryptic compounds. In this study, we explored 72 different Streptomyces-fungus interaction zones (SFIZs) generated during the co-culture of eight Streptomyces and nine fungi. Two SFIZs were selected because they showed an elicitation of anti-bacterial activity compared to mono-cultures. The study of these SFIZs showed that co-culture had a strong impact on the metabolic expression of each partner and enabled the expression of specific compounds. These results show that mimicking the biotic interactions present in this ecological niche is a promising avenue of research to explore the metabolic capacities of Streptomyces and fungi.