Genome-wide CRISPR Screens Reveal Host Factors Critical for SARS-CoV-2 Infection

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Startling Sweet Temptations: Hedonic Chocolate Deprivation Modulates Experience,Eating Behavior,and Eyeblink Startle

Many individuals restrict their food intake to prevent weight gain. This restriction has both homeostatic and hedonic effects but their relative contribution is currently unclear. To isolate hedonic effects of food restriction, we exposed regular chocolate eaters to one week of chocolate deprivation but otherwise regular eating. Before and after this hedonic deprivation, participants viewed images of chocolate and images of high-calorie but non-chocolate containing foods, while experiential, behavioral and eyeblink startle responses were measured. Compared to satiety, hedonic deprivation triggered increased chocolate wanting, liking, and chocolate consumption but also feelings of frustration and startle potentiation during the intertrial intervals. Deprivation was further characterized by startle inhibition during both chocolate and food images relative to the intertrial intervals. Individuals who responded with frustration to the manipulation and those who scored high on a questionnaire of impulsivity showed more relative startle inhibition. The results reveal the profound effects of hedonic deprivation on experiential, behavioral and attentional/appetitive response systems and underscore the role of individual differences and state variables for startle modulation. Implications for dieting research and practice as well as for eating and weight disorders are discussed.     

Structural Differences between Aβ(1-40) Intermediate Oligomers and Fibrils Elucidated by Proteolytic Fragmentation and Hydrogen/Deuterium Exchange

The aggregation of amyloid-β protein (Aβ) in vivo is a critical pathological event in Alzheimer's disease. Although more and more evidence shows that the intermediate oligomers are the primary neurotoxic species in Alzheimer's disease, the particular structural features responsible for the toxicity of these intermediates are poorly understood. We measured the peptide level solvent accessibility of multiple Aβ(1-40) aggregated states using hydrogen exchange detected by mass spectrometry. A gradual reduction in solvent accessibility, spreading from the C-terminal region to the N-terminal region was observed with ever more aggregated states of Aβ peptide. The observed hydrogen exchange protection begins with reporter peptides 20-34 and 35-40 in low molecular weight oligomers found in fresh samples and culminates with increasing solvent protection of reporter peptide 1-16 in long time aged fibrillar species. The more solvent exposed structure of intermediate oligomers in the N-termini relative to well-developed fibrils provides a novel explanation for the structure-dependent neurotoxicity of soluble oligomers reported previously.     

CHARACTER DISCRIMINATORY POWER,CHARACTER-SET CONGRUENCE,AND THE CLASSIFICATION OF INDIVIDUALS FROM HYBRID ZONES: AN EXAMPLE USING STONE CRABS (MENIPPE)

Many investigators categorize individuals from hybrid zones to facilitate comparisons among genotypic classes (e.g., parental, F₁, backcross) for comparative studies in which components of fitness or geographic variation are being analyzed. Frequently, multiple character sets representing genetically independent traits are used to classify these individuals and various methodologies are employed to combine the classifications obtained from the different character sets. We adapted the principles of total evidence and taxonomic congruence (two formalized approaches used by systematists in formulating phylogenetic hypotheses) to address the problem of discriminating hybridizing species and classifying individuals from hybrid zones. As our model, we used two morphological (coloration and morphometric) and two molecular (allozyme and mitochondrial DNA restriction-fragment-length polymorphism) character sets that differentiate two stone crab species (Menippe adina and M. mercenaria). Using principal-components analysis, we determined that combining character sets and eliminating characters or character sets that did not have large eigenvector coefficients for the principal component that best separated the two species yielded the highest level of discrimination between species and allowed us to classify a broad range of morpho-genotypes as hybrids. For the stone crabs, three diagnostic allozyme loci and five diagnostic coloration characters best separated the species. The two character sets were not completely congruent, but they agreed in their classification of 50% of the individuals from the hybrid zone and rarely strongly disagreed in their classifications. Classification discrepancies between the two character sets probably represent variation between traits in interspecific gene flow rather than intraspecific, ecologically mediated variation. Our results support the assertions of previous investigators who espoused the benefits associated with using multiple character sets to classify individuals from hybrid zones and demonstrate that, if character sets are reasonably congruent and numerically balanced, combining diagnostic characters from multiple character sets (a total-evidence approach) can enhance discriminatory power between species and facilitate the assignment of hybrid-zone individuals to genotypic classes. On the contrary, classifying hybrid-zone individuals using character sets separately (a taxonomic-congruence approach) provides the opportunity to compare levels of introgression between species and to assess reasons for discordance among the data sets.     

Cell surface distribution and intracellular fate of human beta-very low density lipoprotein in cultured peritoneal mouse macrophages: a cytochemical and immunocytochemical study

The receptor-mediated endocytosis pathway of colloidal gold labeled beta-very low density lipoprotein (beta-VLDL-Au) derived from patients with familial dysbetalipoproteinemia was analyzed at the ultrastructural level in macrophages. The results showed that beta-VLDL-Au complexes were specifically recognized by a cell surface receptor of the macrophages. beta-VLDL-Au particles once bound to the randomly distributed cell surface receptors clustered in coated pits and were taken up by coated vesicles. Subsequently, the beta-VLDL-Au particles passed through tubular structures and small endosomes before deposited into large electron lucent smooth surfaced endosomes. As revealed by ruthenium red and enzyme cytochemistry the endosomes appeared to be separated from the extracellular space and did not contain acid phosphatase. There were no clear signs of passage of beta-VLDL through the Golgi complex. The accumulation of many flocculated gold particles within Ac-Pase positive vesicles suggests that beta-VLDL once internalized by the macrophages is diverted into a degradative pathway. Incubation of beta-VLDL-loaded macrophages with the hydrophobic fluorescent dye nile red revealed numerous large fluorescent bodies within the cells indicating that the macrophages accumulate large amounts of lipid droplets with time. Additional studies large amounts of lipid droplets with time. Additional studies with native beta-VLDL in conjunction with postembedding immunocytochemical techniques were used to delineate further the intracellular pathway. Immunolabeling was carried out on thin sections of LR White embedded cells using affinity-purified polyclonal rabbit antibodies against apolipoprotein B with the protein A-gold or goat anti-rabbit IgG-gold technique. Indirect visualization of beta-VLDL by these immunocytochemical studies yielded results comparable to those with gold-labeled beta-VLDL. On the basis of both indirect immunocytochemical and direct cytochemical localization of beta-VLDL it is concluded that although colloidal gold labeling of beta-VLDL molecules unquestionably modifies their morphology, their function appears to be unaltered, at least with respect to the process of receptor-mediated endocytosis.     

Responses of pyriform cortex neurons to excitatory amino acids: Voltage dependence,conductance changes,and effects of divalent cations

The actions of ionophoretically applied N-methyl aspartate (NMA), quisqualate, and kainate, thought to activate three different types of excitatory amino acid receptors, were studied on pyramidal neurons of the rat pyriform cortex, maintained in an isolated, submerged, and perfused brain slice. Intracellular recordings were made with either K acetate or CsCl electrodes. In most neurons all three agonists elicited monophasic responses which could be evoked at 20-sec intervals. Some neurons showed biphasic responses, most commonly to kainate but, on occasion, also for quisqualate. The slower component appeared to be correlated with excitotoxicity and, consequently, was difficult to study. As a result the kainate responses studied were from neurons selected for having a single component. In neurons selected for having a linear current-voltage relationship or neurons loaded with Cs to suppress K conductance and linearize the current-voltage relationship, the average changes in resistance recorded during ionophoretic responses at resting potential were as follows: NMA, 131.2 +/- 6.7% of control; kainate, 104.7 +/- 5.8% of control; and quisqualate, 92.8 +/- 2.8% of control. The magnitude and direction of the conductance change were very reproducible in any one neuron, but especially for kainate some cells showed clear conductance increases, while others showed clear conductance decreases. Using CsCl electrodes it was possible to reduce K+ conductance and depolarize the neurons over a wider range. By passing depolarizing current it was possible to reverse the responses. The response to all three agonists reversed at the same depolarized potential. This observation indicates that while there are differences in the ionic channels associated with the three agonists at resting potential, the channels have similar properties at more depolarized potentials. Responses to all three agonists were influenced by the concentrations of divalent cations in the perfusion medium. The NMA responses were most sensitive to Mg, increasing in amplitude in the absence of Mg and being depressed by Mg elevation. All responses were sensitive to Ca, with discharges being greatly increased by low Ca and depressed by high Ca. The kainate response was most sensitive to Ca concentration changes. Unlike reports from other preparations the apparent conductance decreases to NMA were not altered by the perfusion of solutions with either no added Mg or no added Ca. The NMA response was very much reduced in either Co (1-2 mM) or Zn (100-200 microM).(ABSTRACT TRUNCATED AT 400 WORDS)     

Synchrony of bone marrow proliferation and maturation as the origin of cyclic haemopoiesis

Abstract. Cyclic haemopoiesis in Grey Collie dogs is characterized by stable oscillations in all haemopoietic lineages. It is proposed that in these animals, in contrast to normal animals, the maturation process of haemopoietic (in particular granuloid) cells from the primitive progenitors to the functional cells is characterized by an abnormally strong synchrony. It is conjectured that the marrow maturation time has a very small variance compared with non-cyclic normal dogs. With a mathematical model of haemopoiesis it is shown that small fluctuations are amplified via regular feedback processes such that stable granuloid oscillations are established. Erythroid oscillations are induced indirectly by granuloid feedback to the stem cell pool. The model calculations further show that the synchrony hypothesis of bone marrow maturation can quantitatively explain the following experimental results: (1) the maintenance of stable cycles of granuloid and erythroid bone marrow and blood cells with a period of approximately 14 d; (2) the disappearance of granuloid and erythroid cycles during the administration of the colony stimulating factor rhG-CSF; (3) the reappearance of oscillations when the administration of CSF is discontinued; (4) the cessation of cycles during endotoxin application; and (5) the persistence of cycles during erythroid manipulations (bleeding anaemia, hypoxia, hypertransfusion). We therefore conclude that cyclic haemopoiesis is not caused by a defect in the regulatory control system but by an unusual maturation process.