Nanostructures from the self‐assembly of α‐helical peptide amphiphiles

Self‐assembly of PAs composed of palmitic acid and several repeated heptad peptide sequences, C₁₅H₃₁CO‐(IEEYTKK)_n‐NH₂ (n = 1–4, represented by PA1–PA4), was investigated systematically. The secondary structures of the PAs were characterized by CD. PA3 and PA4 (n = 3 and 4, respectively) showed an α‐helical structure, whereas PA1 and PA2 (n = 1 and 2, respectively) did not display an α‐helical conformations under the tested conditions. The morphology of the self‐assembled peptides in aqueous medium was studied by transmission electron microscopy. As the number of heptad repeats in the PAs increased, the nanostructure of the self‐assembled peptides changed from nanofibers to nanovesicles. Changes of the secondary structures and the self‐assembly morphologies of PA3 and PA4 in aqueous medium with various cations were also studied. The critical micelle concentrations were determined using a pyrene fluorescence probe. In conclusion, this method may be used to design new peptide nanomaterials. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

Identification of a recently active Prunus‐specific non‐autonomous Mutator element with considerable genome shaping force

Miniature inverted‐repeat transposable elements (MITEs) are known to contribute to the evolution of plants, but only limited information is available for MITEs in the Prunus genome. We identified a MITE that has been named Falling Stones, FaSt. All structural features (349‐bp size, 82‐bp terminal inverted repeats and 9‐bp target site duplications) are consistent with this MITE being a putative member of the Mutator transposase superfamily. FaSt showed a preferential accumulation in the short AT‐rich segments of the euchromatin region of the peach genome. DNA sequencing and pollination experiments have been performed to confirm that the nested insertion of FaSt into the S‐haplotype‐specific F‐box gene of apricot resulted in the breakdown of self‐incompatibility (SI). A bioinformatics‐based survey of the known Rosaceae and other genomes and a newly designed polymerase chain reaction (PCR) assay verified the Prunoideae‐specific occurrence of FaSt elements. Phylogenetic analysis suggested a recent activity of FaSt in the Prunus genome. The occurrence of a nested insertion in the apricot genome further supports the recent activity of FaSt in response to abiotic stress conditions. This study reports on a presumably active non‐autonomous Mutator element in Prunus that exhibits a major indirect genome shaping force through inducing loss‐of‐function mutation in the SI locus.     

GENETIC ARCHITECTURE OF INBREEDING DEPRESSION AND THE MAINTENANCE OF GAMETOPHYTIC SELF‐INCOMPATIBILITY

Gametophytic self‐incompatibility (GSI) is a widespread genetic system, which enables hermaphroditic plants to avoid self‐fertilization and mating with close relatives. Inbreeding depression is thought to be the major force maintaining SI; however, inbreeding depression is a dynamical variable that depends in particular on the mating system. In this article we use multilocus, individual‐based simulations to examine the coevolution of SI and inbreeding depression within finite populations. We focus on the conditions for the maintenance of SI when self‐compatible (SC) mutants are introduced in the population by recurrent mutation, and compare simulation results with predictions from an analytical model treating inbreeding depression as a fixed parameter (thereby neglecting effects of purging within the SC subpopulation). In agreement with previous models, we observe that the maintenance of SI is associated with high inbreeding depression and is facilitated by high rates of self‐pollination. Purging of deleterious mutations by SC mutants has little effect on the spread of those mutants as long as most deleterious alleles have weak fitness effects: in this case, the genetic architecture of inbreeding depression has little effect on the maintenance of SI. By contrast, purging may greatly enhance the spread of SC mutants when deleterious alleles have strong fitness effects.     

Extended access of cocaine self‐administration results in tolerance to the dopamine‐elevating and locomotor‐stimulating effects of cocaine

Tolerance to the neurochemical and psychoactive effects of cocaine after repeated use is a hallmark of cocaine addiction in humans. However, comprehensive studies on tolerance to the behavioral, psychoactive, and neurochemical effects of cocaine following contingent administration in rodents are lacking. We outlined the consequences of extended access cocaine self‐administration as it related to tolerance to the psychomotor activating, dopamine (DA) elevating, and DA transporter (DAT) inhibiting effects of cocaine. Cocaine self‐administration (1.5 mg/kg/inj; 40 inj; 5 days), which resulted in escalation of first hour intake, caused reductions in evoked DA release and reduced maximal rates of uptake through the DAT as measured by slice voltammetry in the nucleus accumbens core. Furthermore, we report reductions in cocaine‐induced uptake inhibition and a corresponding increase in the dose of cocaine required for 50% inhibition of DA uptake (K_i) at the DAT. Cocaine tolerance at the DAT translated to reductions in cocaine‐induced DA overflow as measured by microdialysis. In addition, cocaine‐induced elevations in locomotor activity and stereotypy were reduced, while rearing behavior was enhanced in animals with a history of cocaine self‐administration. Here, we demonstrate both neurochemical and behavioral cocaine tolerance in an extended‐access rodent model of cocaine abuse, which allows for a better understanding of the neurochemical and psychomotor tolerance that develops to cocaine in human addicts.

     

Structural and dynamical characterization of tubular HIV‐1 capsid protein assemblies by solid state nuclear magnetic resonance and electron microscopy

The wild‐type HIV‐1 capsid protein (CA) self‐assembles in vitro into tubular structures at high ionic strength. We report solid state nuclear magnetic resonance (NMR) and electron microscopy measurements on these tubular CA assemblies, which are believed to contain a triangular lattice of hexameric CA proteins that is similar or identical to the lattice of capsids in intact HIV‐1. Mass‐per‐length values of CA assemblies determined by dark‐field transmission electron microscopy indicate a variety of structures, ranging from single‐wall tubes to multiwall tubes that approximate solid rods. Two‐dimensional (2D) solid state ¹³C? ¹³C and ¹⁵N? ¹³C NMR spectra of uniformly ¹⁵N,¹³C‐labeled CA assemblies are highly congested, as expected for a 25.6 kDa protein in which nearly the entire amino acid sequence is immobilized. Solid state NMR spectra of partially labeled CA assemblies, expressed in 1,3‐¹³C₂‐glycerol medium, are better resolved, allowing the identification of individual signals with line widths below 1 ppm. Comparison of crosspeak patterns in the experimental 2D spectra with simulated patterns based on solution NMR chemical shifts of the individual N‐terminal (NTD) and C‐terminal (CTD) domains indicates that NTD and CTD retain their individual structures upon self‐assembly of full‐length CA into tubes. 2D ¹H‐¹³C NMR spectra of CA assemblies recorded under solution NMR conditions show relatively few signals, primarily from segments that link the α‐helices of NTD and CTD and from the N‐ and C‐terminal ends. Taken together, the data support the idea that CA assemblies contain a highly ordered 2D protein lattice in which the NTD and CTD structures are retained and largely immobilized.     

Ethnic and sex variations in overweight self-perception: relationship to sedentariness

Objective: With increasing frequency, health promotion messages advocating physical activity are claiming weight loss as a benefit. However, messages promoting physical activity as a weight loss strategy may have limited effectiveness and cross‐cultural relevance. We recently found self‐perceived overweight to be a more robust correlate of sedentary behavior than BMI in Los Angeles County adults. In this study, we examined ethnic and sex differences in overweight self‐perception and their association with sedentariness in this sample. Research Methods and Procedures: We conducted bivariate and multivariate analyses of cross‐sectional survey data from a representative sample of Los Angeles County adults. Results: Women were more likely to perceive themselves to be overweight than men overall (73.2% of overweight/non‐obese and 24.1% of average weight women vs. 44.5% of overweight/non‐obese and 5.6% of average weight men) and within each ethnic group. African‐Americans were least likely (41.3% of overweight/non‐obese African‐Americans self‐identified as overweight) and whites were most likely to consider themselves overweight (60.6% of overweight/non‐obese whites self‐identified as overweight). Overweight (vs. average weight) self‐perception was correlated with sedentariness among average weight adults (45.3% vs. 33.0%, p < 0.001), overweight adults (43.4% vs. 33.6%, p < 0.001), men (average and overweight: 38.4% vs. 27.8%, p < 0.001), overweight whites (41.9% vs. 29.7%, p = 0.0012), and African‐Americans and Latinos (41.6% vs. 33.9%, p = 0.005). Discussion: These data suggest that our society's emphasis on weight loss rather than lifestyle change may inadvertently discourage physical activity adoption/maintenance among non‐obese individuals. However, further research is needed, particularly from prospective cohort and intervention studies, to elucidate the relationship between overweight self‐perception and healthy lifestyle change.     

Nanogels prepared by self-assembly of oppositely charged globular proteins

Ovalbumin and lysozyme are two main proteins in hen egg white with the isoelectric points of 4.8 and 11, respectively. Herein we report the manufacture of stable, narrowly distributed nanogels (hydrodynamic radius about 100 nm) using a novel and convenient method: ovalbumin and lysozyme solutions were mixed at pH 5.3, the mixture solution was adjusted to pH 10.3, then subsequently stirred and heated. The nanogels were characterized using a combination of techniques. The nanogels have spherical shape and core-shell structure. The core is mainly composed of lysozyme and the shell is mainly composed of ovalbumin. The proteins in the nanogels are in denatured states and they are bound by intermolecular hydrophobic interactions, hydrogen bonds, and disulfide bonds. The charges of the nanogels can be modulated by the pH of the medium. The electrostatic repulsion of ovalbumin molecules on the nanogel surface stabilizes the nanogels in aqueous solution. The formation mechanism of the nanogels is discussed.     

Noninvasive assessment of adrenal activity associated with husbandry and behavioral factors in the North American clouded leopard population

The North American clouded leopard (Neofelis nebulosa) population is far from self‐sustaining. Breeding success is poor and behavioral problems (i.e., fur‐plucking, tail‐chewing, excessive hiding or pacing, and intersexual aggression that results in mate killing) are common. This study was undertaken to investigate whether some of these problems may be indicators of chronic stress (as reflected by persistently elevated glucocorticoid levels) and whether they are associated with specific management factors. A fecal corticoid metabolite assay was validated to monitor adrenal activity in clouded leopards. Adrenocorticotropic hormone (ACTH) challenges conducted in four clouded leopards established the biological relevance of the assay system. Fecal corticoid concentrations increased 14‐fold above baseline within 24 hours after ACTH administration. Adrenal activity then was monitored in 72 (36 males; 36 females) clouded leopards (65% of the North American Species Survival Plan population) during a 6‐week period and compared to husbandry and behavior data. There was a significant (P < 0.01) gender difference in fecal corticoid concentrations, with females producing higher concentrations than males. Multiple regression analyses revealed negative associations (P < 0.01) between enclosure height, number of hours keepers spent with each animal per week, and corticoid concentrations. A positive correlation (P < 0.001) was found between the number of keepers caring for an individual and corticoid concentrations. Higher fecal corticoid concentrations (P ≤ 0.05) were measured in clouded leopards kept on public display or near potential predators compared to individuals maintained off exhibit or in the absence of predators. Individuals that performed self‐injuring behaviors also had elevated fecal corticoids (P < 0.01). Spearman‐rank correlation analysis of keeper ratings and hormone data revealed positive associations (P ≤ 0.05) between some behaviors (pace, sleep, hide, and fearful/tense) and fecal corticoid concentrations. Overall these results indicate that noninvasive fecal corticoid monitoring has enormous potential for investigating how management and behavioral problems are related to animal well‐being. If conducted under carefully controlled experimental paradigms, this technique could allow researchers and managers to identify problem areas of captive management for clouded leopards (e.g., enclosure height, keeper time) and evaluate the efficacy of strategies designed to promote animal welfare and increased reproductive success. Zoo Biol 21:77–98, 2002. © 2002 Wiley‐Liss, Inc.     

Persistent conditioned place preference to aggression experience in adult male sexually‐experienced CD‐1 mice

We recently developed a conditioned place preference (CPP) procedure, commonly used to study rewarding drug effects, to demonstrate that dominant sexually‐experienced CD‐1 male mice form CPP to contexts previously associated with defeating subordinate male C57BL/6J mice. Here we further characterized conditioned and unconditioned aggression behavior in CD‐1 mice. In Exp. 1 we used CD‐1 mice that displayed a variable spectrum of unconditioned aggressive behavior toward younger subordinate C57BL/6J intruder mice. We then trained the CD‐1 mice in the CPP procedure where one context was intruder‐paired, while a different context was not. We then tested for aggression CPP 1 day after training. In Exp. 2, we tested CD‐1 mice for aggression CPP 1 day and 18 days after training. In Exp. 3–4, we trained the CD‐1 mice to lever‐press for palatable food and tested them for footshock punishment‐induced suppression of food‐reinforced responding. In Exp. 5, we characterized unconditioned aggression in hybrid CD‐1 × C57BL/6J D1‐Cre or D2‐Cre F1 generation crosses. Persistent aggression CPP was observed in CD‐1 mice that either immediately attacked C57BL/6J mice during all screening sessions or mice that gradually developed aggressive behavior during the screening phase. In contrast, CD‐1 mice that did not attack the C57BL/6J mice during screening did not develop CPP to contexts previously paired with C57BL/6J mice. The aggressive phenotype did not predict resistance to punishment‐induced suppression of food‐reinforced responding. CD‐1 × D1‐Cre or D2‐Cre F1 transgenic mice showed strong unconditioned aggression. Our study demonstrates that aggression experience causes persistent CPP and introduces transgenic mice for circuit studies of aggression.     

Network theory and metapopulation persistence: incorporating node self‐connections

Network analysis is gaining increasing importance in conservation planning. However, which network metrics are the best predictors of metapopulation persistence is still unresolved. Here, we identify a critical limitation of graph theory‐derived network metrics that have been proposed for this purpose: their omission of node self‐connections. We resolve this by presenting modifications of existing network metrics, and developing entirely new metrics, that account for node self‐connections. Then, we illustrate the performance of these new and modified metrics with an age‐structured metapopulation model for a real‐world marine reserve network case study, and we evaluate the robustness of our findings by systematically varying particular features of that network. Our new and modified metrics predict metapopulation persistence much better than existing metrics do, even when self‐connections are weak. Existing metrics become good predictors of persistence only when self‐connections are entirely absent, an unrealistic scenario in the overwhelming majority of metapopulation applications. Our study provides a set of novel tools that can substantially enhance the extent to which network metrics can be employed to understand, and manage for, metapopulation persistence.