Maturation of prefrontal input to dorsal raphe increases behavioral persistence in mice

The ability to persist towards a desired objective is a fundamental aspect of behavioral control whose impairment is implicated in several behavioral disorders. One of the prominent features of behavioral persistence is that its maturation occurs relatively late in development. This is presumed to echo the developmental time course of a corresponding circuit within late-maturing parts of the brain, such as the prefrontal cortex, but the specific identity of the responsible circuits is unknown. Here, we describe the maturation of the projection from layer 5 neurons of the prefrontal cortex to the dorsal raphe nucleus in mice. We show using pathway-specific optogenetic stimulation that this connection undergoes a dramatic increase in synaptic potency between postnatal weeks 3 and 8, corresponding to the transition from juvenile to adult. We then show that this period corresponds to an increase in the behavioral persistence that mice exhibit in a foraging task. Finally, we use genetic targeting to selectively ablate this pathway in adulthood and show that mice revert to a behavioral phenotype similar to juveniles. These results suggest that the prefrontal to dorsal raphe pathway is a critical anatomical and functional substrate of the development and manifestation of behavioral control.

Cortical glutamatergic projection neuron types contribute to distinct functional subnetworks

The cellular basis of cerebral cortex functional architecture remains not well understood. A major challenge is to monitor and decipher neural network dynamics across broad cortical areas yet with projection neuron (PN) type resolution in real time during behavior. Combining genetic targeting and wide-field imaging, we monitored activity dynamics of subcortical-projecting (PTFezf2) and intratelencephalic-projecting (ITPlxnD1) types across dorsal cortex of mice during multiple brain states and behaviors. ITPlxnD1 and PTFezf2 showed distinct activation patterns during wakeful resting, spontaneous movements, and upon sensory stimulation. Distinct ITPlxnD1 and PTFezf2 subnetworks dynamically tuned to different sensorimotor components of a naturalistic feeding behavior, and optogenetic inhibition of subnetwork nodes disrupted specific behavioral components. ITPlxnD1 and PTFezf2 projection patterns supported their subnetwork activation patterns. Our results suggest that, in addition to the concept of columnar organization, dynamic areal and PN type-specific subnetworks is a key feature of cortical functional architecture linking microcircuit components with global brain networks.

Genetic targeting of Card19 is linked to disrupted NINJ1 expression, impaired cell lysis, and increased susceptibility to Yersinia infection

Cell death plays a critical role in inflammatory responses. During pyroptosis, inflammatory caspases cleave Gasdermin D (GSDMD) to release an N-terminal fragment that generates plasma membrane pores that mediate cell lysis and IL-1 cytokine release. Terminal cell lysis and IL-1β release following caspase activation can be uncoupled in certain cell types or in response to particular stimuli, a state termed hyperactivation. However, the factors and mechanisms that regulate terminal cell lysis downstream of GSDMD cleavage remain poorly understood. In the course of studies to define regulation of pyroptosis during Yersinia infection, we identified a line of Card19-deficient mice (Card19lxcn) whose macrophages were protected from cell lysis and showed reduced apoptosis and pyroptosis, yet had wild-type levels of caspase activation, IL-1 secretion, and GSDMD cleavage. Unexpectedly, CARD19, a mitochondrial CARD-containing protein, was not directly responsible for this, as an independently-generated CRISPR/Cas9 Card19 knockout mouse line (Card19Null) showed no defect in macrophage cell lysis. Notably, Card19 is located on chromosome 13, immediately adjacent to Ninj1, which was recently found to regulate cell lysis downstream of GSDMD activation. RNA-seq and western blotting revealed that Card19lxcn BMDMs have significantly reduced NINJ1 expression, and reconstitution of Ninj1 in Card19lxcn immortalized BMDMs restored their ability to undergo cell lysis in response to caspase-dependent cell death stimuli. Card19lxcn mice exhibited increased susceptibility to Yersinia infection, whereas independently-generated Card19Null mice did not, demonstrating that cell lysis itself plays a key role in protection against bacterial infection, and that the increased infection susceptibility of Card19lxcn mice is attributable to loss of NINJ1. Our findings identify genetic targeting of Card19 being responsible for off-target effects on the adjacent gene Ninj1, disrupting the ability of macrophages to undergo plasma membrane rupture downstream of gasdermin cleavage and impacting host survival and bacterial control during Yersinia infection.

BUB1B and circBUB1B_544aa aggravate multiple myeloma malignancy through evoking chromosomal instability

Multiple myeloma (MM) is an incurable plasma cell malignancy in the bone marrow characterized by chromosome instability (CIN), which contributes to the acquisition of heterogeneity, along with MM progression, drug resistance, and relapse. In this study, we elucidated that the expression of BUB1B increased strikingly in MM patients and was closely correlated with poor outcomes. Overexpression of BUB1B facilitated cellular proliferation and induced drug resistance in vitro and in vivo, while genetic targeting BUB1B abrogated this effect. Mechanistic studies unveiled that enforced expression of BUB1B evoked CIN resulting in MM poor outcomes mainly through phosphorylating CEP170. Interestingly, we discovered the existence of circBUB1B_544aa containing the kinase catalytic center of BUB1B, which was translated by a circular RNA of BUB1B. The circBUB1B_544aa elevated in MM peripheral blood samples was closely associated with MM poor outcomes and played a synergistic effect with BUB1B on evoking CIN. In addition, MM cells could secrete circBUB1B_544aa and interfere the MM microenvironmental cells in the same manner as BUB1B full-length protein. Intriguingly, BUB1B siRNA, targeting the kinase catalytic center of both BUB1B and circBUB1B_544aa, significantly inhibited MM malignancy in vitro and in vivo. Collectively, BUB1B and circBUB1B_544aa are promising prognostic and therapeutic targets of MM.

Genetic targeting of adult Renshaw cells using a Calbindin 1 destabilized Cre allele for intersection with Parvalbumin or Engrailed1

Renshaw cells (RCs) are one of the most studied spinal interneurons; however, their roles in motor control remain enigmatic in part due to the lack of experimental models to interfere with RC function, specifically in adults. To overcome this limitation, we leveraged the distinct temporal regulation of Calbindin (Calb1) expression in RCs to create genetic models for timed RC manipulation. We used a Calb1 allele expressing a destabilized Cre (dgCre) theoretically active only upon trimethoprim (TMP) administration. TMP timing and dose influenced RC targeting efficiency, which was highest within the first three postnatal weeks, but specificity was low with many other spinal neurons also targeted. In addition, dgCre showed TMP-independent activity resulting in spontaneous recombination events that accumulated with age. Combining Calb1-dgCre with Parvalbumin (Pvalb) or Engrailed1 (En1) Flpo alleles in dual conditional systems increased cellular and timing specificity. Under optimal conditions, Calb1-dgCre/Pvalb-Flpo mice targeted 90% of RCs and few dorsal horn neurons; Calb1-dgCre/En1-Flpo mice showed higher specificity, but only a maximum of 70% of RCs targeted. Both models targeted neurons throughout the brain. Restricted spinal expression was obtained by injecting intraspinally AAVs carrying dual conditional genes. These results describe the first models to genetically target RCs bypassing development.

Classification and genetic targeting of cell types in the primary taste and premotor center of the adult Drosophila brain

Neural circuits carry out complex computations that allow animals to evaluate food, select mates, move toward attractive stimuli, and move away from threats. In insects, the subesophageal zone (SEZ) is a brain region that receives gustatory, pheromonal, and mechanosensory inputs and contributes to the control of diverse behaviors, including feeding, grooming, and locomotion. Despite its importance in sensorimotor transformations, the study of SEZ circuits has been hindered by limited knowledge of the underlying diversity of SEZ neurons. Here, we generate a collection of split-GAL4 lines that provides precise genetic targeting of 138 different SEZ cell types in adult D. melanogaster, comprising approximately one third of all SEZ neurons. We characterize the single cell anatomy of these neurons and find that they cluster by morphology into six supergroups that organize the SEZ into discrete anatomical domains. We find that the majority of local SEZ interneurons are not classically polarized, suggesting rich local processing, whereas SEZ projection neurons tend to be classically polarized, conveying information to a limited number of higher brain regions. This study provides insight into the anatomical organization of the SEZ and generates resources that will facilitate further study of SEZ neurons and their contributions to sensory processing and behavior.

OS06.3A LSD1-directed therapy curtails glioblastoma tumorigenicity by limiting the adaptation of tumor initiating cells to stressful environments

BACKGROUND Glioblastoma (GBM) is a fatal tumor whose aggressiveness, heterogeneity, therapy resistance and poor blood-brain-barrier penetration hinder the amelioration of the standard-of-care. Included in the GBM mass are the tumor initiating cells (TICs), representing the driver of GBM growth and relapse in virtue of their stem-like traits and therapy-resistance. Being constantly exposed to environmental stress, including nutrients deficiency, hypoxia and therapeutic insults, all GBM cells -and TICs in particular- have to be highly adaptive in order to survive. Thus, their ability to cope with stress could be targeted to curtail TICs maintenance and the whole GBM aggressiveness. The key of TICs adaptation relies, among the others, on their epigenetic plasticity, hence encouraging epigenetic drugs testing. MATERIAL AND METHODS By exploiting patient-derived GBM TICs and orthotopic xenograft models, we tested the antitumorigenic features of a novel, selective, orally bioavailable and brain-penetrant Lysine-specific histone demethylase 1 inhibitor (LSD1i). We confirmed the specificity of its effects by LSD1 genetic targeting. A combination of RNA-seq, Chromatin Immunoprecipitation(ChIP)-seq, Mass Spectrometry and reverse genetic experiments unraveled LSD1 molecular players in GBM TICs. RESULTS We identified LSD1 as a druggable target in human GBM: LSD1i treatment, mirrored by LSD1 genetic targeting, impairs growth, viability, stem-like traits and in vivo tumorigenicity of GBM TICs. Mechanistically, LSD1 is crucial for the expression of the activating transcription factor 4 (ATF4), which coordinates the integrated stress response (ISR) to manage stressful stimuli as nutrient deprivation and endoplasmic reticulum stress. By mimicking these stress cues in vitro, we found that LSD1i triggers a delayed but unabated ATF4 translation which provokes an over-lasting ISR, eventually culminating in GBM TICs apoptosis. Lastly, LSD1 demethylase activity is dispensable for ATF4 induction. Rather, LSD1i exerts its anti-tumorigenic potential by interfering with LSD1 scaffolding function in GBM TICs. CONCLUSION LSD1-directed therapy is likely a promising strategy to hinder GBM. By sensitizing GBM TICs to stress, LSD1i endangers the GBM TICs pool. The effectiveness of LSD1i administration in different patient-derived GBM TICs and xenografts, regardless of their molecular profile, places a strong rationale toward the clinical translation of this approach for GBM management. FUNDING Italian association for Cancer Research (AIRC) and Italian Ministry of Health

Classification and genetic targeting of cell types in the primary taste and premotor center of the Drosophila brain

Neural circuits carry out complex computations that allow animals to evaluate food, select mates, move toward attractive stimuli, and move away from threats. In insects, the subesophageal zone (SEZ) is a brain region that receives gustatory, pheromonal, and mechanosensory inputs and contributes to the control of diverse behaviors, including feeding, grooming, and locomotion. Despite its importance in sensorimotor transformations, the study of SEZ circuits has been hindered by limited knowledge of the underlying diversity of SEZ neurons. Here, we generate a collection of split-GAL4 lines that provides precise genetic targeting of 138 different SEZ cell types in adult D. melanogaster, comprising approximately one third of all SEZ neurons. We characterize the single cell anatomy of these neurons and find that they cluster by morphology into six supergroups that organize the SEZ into discrete anatomical domains. We find that the majority of local SEZ interneurons are not classically polarized, suggesting rich local processing, whereas SEZ projection neurons tend to be classically polarized, conveying information to a limited number of higher brain regions. This study provides insight into the anatomical organization of the SEZ and generates resources that will facilitate further study of SEZ neurons and their contributions to sensory processing and behavior.

Mechanical forces regulate endothelial-to-mesenchymal transition and atherosclerosis via an Alk5-Shc mechanotransduction pathway

The response of endothelial cells to mechanical forces is a critical determinant of vascular health. Vascular pathologies, such as atherosclerosis, characterized by abnormal mechanical forces are frequently accompanied by endothelial-to-mesenchymal transition (EndMT). However, how forces affect the mechanotransduction pathways controlling cellular plasticity, inflammation, and, ultimately, vessel pathology is poorly understood. Here, we identify a mechanoreceptor that is sui generis for EndMT and unveil a molecular Alk5-Shc pathway that leads to EndMT and atherosclerosis. Depletion of Alk5 abrogates shear stress–induced EndMT responses, and genetic targeting of endothelial Shc reduces EndMT and atherosclerosis in areas of disturbed flow. Tensional force and reconstitution experiments reveal a mechanosensory function for Alk5 in EndMT signaling that is unique and independent of other mechanosensors. Our findings are of fundamental importance for understanding how mechanical forces regulate biochemical signaling, cell plasticity, and vascular disease.

Genetic fate-mapping reveals surface accumulation but not deep organ invasion of pleural and peritoneal cavity macrophages following injury

During injury, monocytes are recruited from the circulation to inflamed tissues and differentiate locally into mature macrophages, with prior reports showing that cavity macrophages of the peritoneum and pericardium invade deeply into the respective organs to promote repair. Here we report a dual recombinase-mediated genetic system designed to trace cavity macrophages in vivo by intersectional detection of two characteristic markers. Lineage tracing with this method shows accumulation of cavity macrophages during lung and liver injury on the surface of visceral organs without penetration into the parenchyma. Additional data suggest that these peritoneal or pleural cavity macrophages do not contribute to tissue repair and regeneration. Our in vivo genetic targeting approach thus provides a reliable method to identify and characterize cavity macrophages during their development and in tissue repair and regeneration, and distinguishes these cells from other lineages.