The rockefeller university

Proper fuelling of the brain is critical to sustain cognitive function, but the role of fatty acid (FA) combustion in this process has been elusive. Here we show that acute block of a neuron-specific triglyceride lipase, DDHD2 (a genetic driver of complex hereditary spastic paraplegia), or of the mitochondrial lipid transporter CPT1 leads to rapid onset of torpor in adult male mice. These data indicate that in vivo neurons are probably constantly fluxing FAs derived from lipid droplets (LDs) through beta-oxidation to support neuronal bioenergetics. We show that in dissociated neurons, electrical silencing or blocking of DDHD2 leads to accumulation of neuronal LDs, including at nerve terminals, and that FAs derived from axonal LDs enter mitochondria in an activity-dependent fashion to drive local mitochondrial ATP production. These data demonstrate that nerve terminals can make use of LDs during electrical activity to provide metabolic support and probably have a critical role in supporting neuron function in vivo.

Isocitrate dehydrogenase 1/2 (IDH) mutations are early initiating events in acute myeloid leukemia (AML). The complex clonal architecture and cellular heterogeneity in IDH-mutant AML underlies the heterogeneous clinical presentation and outcomes. Integrating single-cell genotyping and transcriptomics, we demonstrate a stem-like and inflammatory phenotype of IDH-mutant AML and identify clone-specific programs associated with NPM1, NRAS, and SRSF2 co-mutations. Furthermore, these clones had distinct responses to treatment with combination IDH inhibitors and chemotherapy, including elimination, reconstitution of myeloid differentiation, or retention within progenitor populations. At relapse after IDH inhibitor monotherapy, we identify up-regulated stemness, inflammation, mitochondrial metabolism, and anti-apoptotic factors, as well as down-regulated major histocompatibility complex (MHC) class II antigen presentation. At the pre-leukemic stage, we observe upregulation of IDH2-associated pathways, including inflammation. We deliver a detailed phenotyping of IDH-mutant AML and a framework for dissecting contributions of recurrently mutated genes in AML at diagnosis and following therapy, with implications for precision medicine.

A critical component of the function of IgG antibodies is their capacity to engage specialized cellular receptors, Fc gamma receptors (Fc gamma Rs), expressed on effector leukocytes. Highlighting the importance of Fc gamma R-mediated signaling in the regulation of the fate, activation, and differentiation status of leukocytes, Fc gamma Rs are ubiquitously expressed by nearly all leukocyte populations. Here, we report that while at steady state, T cells are negative for all classes of Fc gamma Rs, CD8 T cells specifically induce the expression of the activating Fc gamma R, Fc gamma RIIIa, in response to viral infection in cohorts of COVID-19 and dengue patients, as well as in virus infection models using Fc gamma R humanized mouse strains. In in vivo mechanistic studies, we demonstrate that induction of Fc gamma RIIIa expression on effector CD8 T cells follows a well-defined trajectory that closely tracks the course and magnitude of the immune response, while immune resolution is characterized by receptor downregulation. Uniquely to these CD8 T cells, Fc gamma RIIIa crosslinking alone is paradoxically insufficient to elicit T cell activation and cytotoxicity. However, when coupled with T cell receptor (TCR) stimulation, it results in synergistic cellular activation and, compensates for the downregulation of canonical costimulatory molecules on terminal effector CD8 T cells. These results reveal a previously unappreciated role for Fc gamma RIIIa as a unique costimulatory molecule that synergizes with TCR signaling to lower the effective threshold required for CD8 T cell activation, highlighting the role of virally induced antibodies in modulating CD8 effector cell responses.

Clinical and animal studies suggest that multiple brain systems are involved in mediating reward-motivated and related emotional behavior including the consumption of commonly used drugs and palatable food, and there is evidence that the repeated ingestion of or exposure to these rewarding substances may in turn stimulate these brain systems to produce an overconsumption of these substances along with co-occurring emotional disturbances. To understand this positive feedback loop, this review focuses on a specific population of hypothalamic peptide neurons expressing melanin-concentrating hormone (MCH), which are positively related to dopamine reward and project to forebrain areas that mediate this behavior. It also examines neurons expressing the peptide hypocretin/orexin (HCRT) that are anatomically and functionally linked to MCH neurons and the molecular systems within these peptide neurons that stimulate their development and ultimately affect behavior. This report first describes evidence in animals that exposure in adults and during adolescence to rewarding substances, such as the drugs alcohol, nicotine and cocaine and palatable fat-rich food, stimulates the expression of MCH as well as HCRT and their intracellular molecular systems. It also increases reward-seeking and emotional behavior, leading to excess consumption and abuse of these substances and neurological conditions, completing this positive feedback loop. Next, this review focuses on the model involving embryonic exposure to these rewarding substances. In addition to revealing a similar positive feedback circuit, this model greatly advances our understanding of the diverse changes that occur in these neuropeptide/molecular systems in the embryo and how they relate, perhaps causally, to the disturbances in behavior early in life that predict a later increased risk of developing substance use disorders. Studies using this model demonstrate in animals that embryonic exposure to these rewarding substances, in addition to stimulating the expression of peptide neurons, increases the intracellular molecular systems in neuroprogenitor cells that promote their development. It also alters the morphology, migration, location and neurochemical profile of the peptide neurons and causes them to develop aberrant neuronal projections to forebrain structures. Moreover, it produces disturbances in behavior at a young age, which are sex-dependent and occur in females more than in males, that can be directly linked to the neuropeptide/molecular changes in the embryo and predict the development of behavioral disorders later in life. These results supporting the close relationship between the brain and behavior are consistent with clinical studies, showing females to be more vulnerable than males to developing substance use disorders with co-occurring emotional conditions and female offspring to respond more adversely than male offspring to prenatal exposure to rewarding substances. It is concluded that the continued consumption of or exposure to rewarding substances at any stage of life can, through such peptide brain systems, significantly increase an individual's vulnerability to developing neurological disorders such as substance use disorders, anxiety, depression, or cognitive impairments.

While human and mouse memory B cells (MBCs) can express the transcription factor T-bet, its role in regulating MBC function remains unclear. We characterized multiple transcriptionally distinct clusters of mature, somatically mutated nucleoprotein (NP)-specific MBCs in lymph nodes (LNs) and lungs of influenza-infected mice. Although none of the MBCs expressed the plasma cell (PC) lineage commitment factor Blimp1, one cluster was enriched for Tbx21+ cells. Similar to the previously described human T-bet + effector MBC (eMBC) population, Tbx21+ mouse MBCs upregulated gene networks associated with effector metabolism, protein synthesis, and the unfolded protein response. Constitutive and inducible ablation of T-bet in murine B cells showed that T-bet expression by MBCs was required for persistence of LN and lung eMBCs with rapid in vitro and in vivo PC differentiation potential. Thus, T-bet marks NP + eMBCs that are poised to differentiate, and it regulates maintenance of lung-resident MBCs and local PC responses following virus re-exposure.

Replicative helicases are assembled on chromosomes by helicase loaders before the initiation of DNA replication. Here, we investigate the mechanisms employed by the bacterial Vibrio cholerae (Vc) DnaB replicative helicase and the DciA helicase loader. Structural analysis of the ATP gamma S form of the VcDnaB-ssDNA complex reveals a configuration distinct from that observed with GDP center dot AlF4. With ATP gamma S, the amino-terminal domain (NTD) tier, previously found as an open spiral in the GDP center dot AlF4 complex, adopts a closed planar arrangement. Furthermore, the DnaB subunit at the top of the carboxy-terminal domain (CTD) spiral is displaced by approximately 25 & Aring; between the two forms. We suggest that remodeling the NTD layer between closed planar and open spiral configurations, along with the migration of two distinct CTDs to the top of the DnaB spiral, repeated three times, mediates hand-over-hand translocation. Biochemical analysis indicates that VcDciA utilizes its Lasso domain to interact with DnaB near its Docking-Helix Linker-Helix interface. Up to three copies of VcDciA bind to VcDnaB, suppressing its ATPase activity during loading onto physiological DNA substrates. Our data suggest that DciA loads DnaB onto DNA using the ring-opening mechanism.

Polyphenic traits in animals often exhibit nonlinear scaling with body size. Static allometries (i.e., scaling relationships) themselves can exhibit plasticity, such that individuals of the same size and genotype differ in body proportions across different environments. In ants, both larval environment and genotype regulate the expression of caste- associated traits, including body size and ovariole number. However, it remains untested whether caste- associated traits are independently regulated by environmental variables or whether they covary due to coupled developmental mechanisms. If caste traits are regulated independently, developmental plasticity should affect both trait expression and the scaling relationships between traits. Using the clonal raider ant, Ooceraea biroi, we tested this by manipulating the rearing environment of genetically identical larvae. We found that caregiver genotype, temperature, and food quantity influenced caste morphology strictly in tandem with body size, producing similar static allometries across rearing conditions (i.e., no allometric plasticity was detected). In contrast, clonal genotypes differed in average body size and their static allometries. Thus, size- matched individuals of the same genotype from different rearing environments exhibited no differences in mean caste trait expression, while those of different genotypes did. This absence of plasticity in the static allometries of different caste traits suggests that they are developmentally coupled due to systemic regulatory factors. Our findings contrast with reports of allometric plasticity in other insects, suggesting that ant caste traits are exceptionally integrated and therefore constrained in their independent responses to environmental variation. We discuss how these results inform contemporary hypotheses for ant caste development and evolution.

Motivated by recent data pointing to the existence of homo- oligomeric assemblies of membrane proteins called higher- order transient structures, and their apparent role in connecting components of membrane signal pathways, we examine here by cryoelectron microscopy some of the protein-protein interactions that occur in cluster formation. Metabotropic glutamate receptors and HCN ion channels inside clusters contact their neighbors through structured extracellular and intracellular domains, respectively. Other ion channels, including Kv2.1 and Slo1, appear to form clusters through prominent intrinsically disordered sequences in the cytoplasm. These distinct modes of interaction are associated with clusters exhibiting varying degrees of compactness and order. We conclude that nature utilizes a variety of ways to form connections between membrane proteins in self- assembled clusters.

Postmitotic neurons have high levels of methylated cytosine and its oxidized intermediates such as 5-hydroxymethylcytosine1. However, the functional relevance of these epigenetic modifications of DNA are poorly understood. Here we show that some cytidine analogues, such as cytarabine, cause DNA double-strand breaks during TET-mediated active 5-methylcytosine demethylation by interrupting TDG-dependent base excision repair. These double-strand breaks are frequently converted into deletions and translocations by DNA ligase 4. In vivo, Purkinje and Golgi cells in the cerebellum are the only neuronal populations that exhibit high levels of DNA damage due to cytarabine. In Purkinje cells, TET targets highly expressed gene bodies marked by enhancer-associated histone modifications. Many of these genes control movement coordination, which explains the long-recognized cerebellar neurotoxicity of cytarabine2. We show that other cytidine analogues, such as gemcitabine, cause only single-strand breaks in neurons, which are repaired by DNA ligase 3 with minimal toxicity. Our findings uncover a mechanistic link between TET-mediated DNA demethylation, base excision repair and gene expression in neurons. The results also provide a rational explanation for the different neurotoxicity profiles of an important class of antineoplastic agents.