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Although oncogenic mutations predispose tissue stem cells to tumor initiation, the rate-limiting processes for stem cell immortalization remain unknown. In this issue of Cell, Bonnay et al. identify enhanced electron transport chain activity as a critical determinant of this process, establishing metabolic reprogramming as limiting for tumor initiation.

BACKGROUND: Parvalbumin (PV)-expressing interneurons are important for cognitive and emotional behaviors. These neurons express high levels of p11, a protein associated with depression and action of antidepressants. METHODS: We characterized the behavioral response to subthreshold stress in mice with conditional deletion of p11 in PV cells. Using chemogenetics, viral-mediated gene delivery, and a specific ion channel agonist, we studied the role of dentate gyrus PV cells in regulating anxiety-like behavior and resilience to stress. We used electrophysiology, imaging, and biochemical studies in mice and cells to elucidate the function and mechanism of p11 in dentate gyrus PV cells. RESULTS: p11 regulates the subcellular localization and cellular level of the potassium channel Kv3.1 in cells. Deletion of p11 from PV cells resulted in reduced hippocampal level of Kv3.1, attenuated capacity of high-frequency firing in dentate gyrus PV cells, and altered short-term plasticity at synapses on granule cells, as well as anxiety-like behavior and a pattern separation deficit. Chemogenetic inhibition or deletion of p11 in these cells induced vulnerability to depressive behavior, whereas upregulation of Kv3.1 in dentate gyrus PV cells or acute activation of Kv3.1 using a specific agonist induced resilience to depression. CONCLUSIONS: The activity of dentate gyrus PV cells plays a major role in the behavioral response to novelty and stress. Activation of the Kv3.1 channel in dentate gyrus PV cells may represent a target for the development of celltype specific, fast-acting antidepressants.

Chromothripsis and kataegis are frequently observed in cancer and may arise from telomere crisis, a period of genome instability during tumorigenesis when depletion of the telomere reserve generates unstable dicentric chromosomes(1-5). Here we examine the mechanism underlying chromothripsis and kataegis by using an in vitro telomere crisis model. We show that the cytoplasmic exonuclease TREX1, which promotes the resolution of dicentric chromosomes(4), plays a prominent role in chromothriptic fragmentation. In the absence of TREX1, the genome alterations induced by telomere crisis primarily involve breakage-fusion-bridge cycles and simple genome rearrangements rather than chromothripsis. Furthermore, we show that the kataegis observed at chromothriptic breakpoints is the consequence of cytosine deamination by APOBEC3B. These data reveal that chromothripsis and kataegis arise from a combination of nucleolytic processing by TREX1 and cytosine editing by APOBEC3B. Nucleic acid processing by the cytoplasmic exonuclease TREX1 and cytosine editing by APOBEC3B drive chromothripsis and kataegis during telomere crisis.

Semisynthetic rifamycin derivatives such as rifampicin (Rif) are first line treatments for tuberculosis and other bacterial infections. Historically, synthetic modifications made to the C-3/C-4 region of the rifamycin naphthalene core, like those seen in Rif, have yielded the biggest improvements in pharmacological properties. However, modifications found in natural product rifamycin congeners occur at other positions in the structure. The kanglemycins (Kangs) are a family of rifamycin congeners with a unique collection of natural modifications including a dimethylsuccinic acid appended to their polyketide backbone. These modifications confer activity against the single most common clinically relevant Rif resistance (Rif(R)) mutation in the antibiotic's target, the bacterial RNA polymerase (RNAP). Here we evaluate the in vivo efficacy of Kang A, the parent compound in the Kang family, in a murine model of bacterial peritonitis/sepsis. We then set out to improve its potency by combining its natural tailoring modifications with semisynthetic derivatizations at either its acid moiety or in the C-3/C-4 region. A collection of C-3/C-4 benzoxazino Kang derivatives exhibit improved activity against wild-type bacteria, and acquire activity against the second most common clinically relevant Rif(R) mutation. The semisynthetic analogue 3'-hydroxy-5'-[4-isobutyl-1-piperazinyl] benzoxazino Kang A (Kang KZ) protected mice against infection with either Rif sensitive MRSA or a highly virulent Rif(R) Staphylococcus aureus strain in a neutropenic peritonitis/sepsis model and led to reduced bacterial burdens. The compounds generated in this study may represent promising candidates for treating Rif(R) infections.

A strategy for assessing the effectiveness of different strategies for HIV cure is presented. Therapeutic strategies are being clinically tested either to eradicate latent HIV reservoirs or to achieve virologic control in the absence of antiretroviral therapy. Attaining this goal will require a consensus on how best to measure the numbers of persistently infected cells with the potential to cause viral rebound after antiretroviral-therapy cessation in assessing the results of cure-directed strategies in vivo. Current measurements assess various aspects of the HIV provirus and its functionality and produce divergent results. Here, we provide recommendations from the BEAT-HIV Martin Delaney Collaboratory on which viral measurements should be prioritized in HIV-cure-directed clinical trials.

SARS-CoV-2 is the causative agent of the 2019-2020 pandemic. The SARS-CoV-2 genome is replicated and transcribed by the RNA-dependent RNA polymerase holoenzyme (subunits nsp7/nsp82/nsp12) along with a cast of accessory factors. One of these factors is the nsp13 helicase. Both the holo-RdRp and nsp13 are essential for viral replication and are targets for treating the disease COVID-19. Here we present cryoelectron microscopic structures of the SARS-CoV-2 holo-RdRp with an RNA template product in complex with two molecules of the nsp13 helicase. The Nidovirales order-specific N-terminal domains of each nsp13 interact with the N-terminal extension of each copy of nsp8. One nsp13 also contacts the nsp12 thumb. The structure places the nucleic acid-binding ATPase domains of the helicase directly in front of the replicating-transcribing holo-RdRp, constraining models for nsp13 function. We also observe ADP-Mg2+ bound in the nsp12 N-terminal nidovirus RdRp-associated nucleotidyltransferase domain, detailing a new pocket for anti-viral therapy development.

Fluctuations in population abundances are often correlated through time across multiple locations, a phenomenon known as spatial synchrony. Spatial synchrony can exhibit complex spatial structures, termed 'geographies of synchrony', that can reveal mechanisms underlying population fluctuations. However, most studies have focused on spatial extents of 10s to 100s of kilometres, making it unclear how synchrony concepts and approaches should apply to dynamics at finer spatial scales. We used network analyses, multiple regression on similarity matrices, and wavelet coherence analyses to examine micro-scale synchrony and geographies of synchrony, over distances up to 30 m, in a serpentine grassland plant community. We found that species' populations exhibited a geography of synchrony even over such short distances. Often, well-synchronized populations were geographically separate, a spatial structure that was shaped mainly by gopher disturbance and dispersal limitation, and to a lesser extent by relationships with other plant species. Precipitation was a significant driver of site- and community-wide temporal dynamics. Gopher disturbance appeared to drive synchrony on 2- to 6-year timescales, and we detected coherent fluctuations among pairs of focal plant taxa. Synthesis. Micro-geographies of synchrony are an intriguing phenomenon that may also help us better understand community dynamics. Additionally, the related geographies of synchrony and coherent temporal dynamics among some species pairs indicate that incorporating interspecific interactions can improve understanding of population spatial synchrony.

Stress has pleiotropic physiologic effects, but the neural circuits linking stress to these responses are not well understood. Here, we describe a novel population of lateral septum neurons expressing neurotensin (LSNts) in mice that are selectively tuned to specific types of stress. LSNts neurons increase their activity during active escape, responding to stress when flight is a viable option, but not when associated with freezing or immobility. Chemogenetic activation of LSNts neurons decreases food intake and body weight, without altering locomotion and anxiety. LSNts neurons co-express several molecules including Glp1r (glucagon-like peptide one receptor) and manipulations of Glp1r signaling in the LS recapitulates the behavioral effects of LSNts activation. Activation of LSNts terminals in the lateral hypothalamus (LH) also decreases food intake. These results show that LSNts neurons are selectively tuned to active escape stress and can reduce food consumption via effects on hypothalamic pathways.

Simple Summary Hepatoblastoma is the most common childhood liver cancer, making up over 90% of malignant liver tumors in children younger than 5 years of age. Currently, research to find new treatments for treatment-resistant hepatoblastoma is limited by a lack of appropriate models to study the disease. In this study, we describe a novel patient-derived organoid model of aggressive hepatoblastoma that can be used to study the disease in the laboratory and test new treatments. We demonstrate that tumor organoids share the same genomic profile as the patient tumors from which they are derived, and also demonstrate similar features with respect to gene expression profiles and beta-catenin signaling. We also demonstrate the feasibility of using hepatoblastoma organoids to complete a drug screen alongside normal liver control organoids derived from the same patient, and report promising initial results of anti-tumor activity of the BET inhibitor JQ1. Hepatoblastoma is the most common childhood liver cancer. Although survival has improved significantly over the past few decades, there remains a group of children with aggressive disease who do not respond to current treatment regimens. There is a critical need for novel models to study aggressive hepatoblastoma as research to find new treatments is hampered by the small number of laboratory models of the disease. Organoids have emerged as robust models for many diseases, including cancer. We have generated and characterized a novel organoid model of aggressive hepatoblastoma directly from freshly resected patient tumors as a proof of concept for this approach. Hepatoblastoma tumor organoids recapitulate the key elements of patient tumors, including tumor architecture, mutational profile, gene expression patterns, and features of Wnt/beta-catenin signaling that are hallmarks of hepatoblastoma pathophysiology. Tumor organoids were successfully used alongside non-tumor liver organoids from the same patient to perform a drug screen using twelve candidate compounds. One drug, JQ1, demonstrated increased destruction of liver organoids from hepatoblastoma tumor tissue relative to organoids from the adjacent non-tumor liver. Our findings suggest that hepatoblastoma organoids could be used for a variety of applications and have the potential to improve treatment options for the subset of hepatoblastoma patients who do not respond to existing treatments.

The actin cytoskeleton mediates mechanical coupling between cells and their tissue microenvironments. The architecture and composition of actin networks are modulated by force; however, it is unclear how interactions between actin filaments (F-actin) and associated proteins are mechanically regulated. Here we employ both optical trapping and biochemical reconstitution with myosin motor proteins to show single piconewton forces applied solely to F-actin enhance binding by the human version of the essential cell-cell adhesion protein alpha E-catenin but not its homolog vinculin. Cryo-electron microscopy structures of both proteins bound to F-actin reveal unique rearrangements that facilitate their flexible C-termini refolding to engage distinct interfaces. Truncating alpha-catenin's C-terminus eliminates force-activated F-actin binding, and addition of this motif to vinculin confers force-activated binding, demonstrating that alpha-catenin's C-terminus is a modular detector of F-actin tension. Our studies establish that piconewton force on F-actin can enhance partner binding, which we propose mechanically regulates cellular adhesion through alpha-catenin.