Regulation of Listeria virulence: PrfA master and commander

Listeria monocytogenes is the causative agent of listeriosis, a severe foodborne infection. These bacteria live as soil saprotrophs on decaying plant matter but also as intracellular parasites, using the cell cytosol as a replication niche. PrfA, a regulatory protein, integrates a number of environmental cues that signal the transition between these two contrasting lifestyles, activating a set of key virulence factors during host infection. While a number of details concerning the general mode of action of this virulence master switch have been elucidated, others remain unsolved. Recent work has revealed additional mechanisms that contribute to L. monocytogenes virulence modulation, often via cross-talk with PrfA, or by regulating new genes involved in host colonization.     

RT-qPCR reveals opsin gene upregulation associated with age and sex in guppies (Poecilia reticulata) - a species with color-based sexual selection and 11 visual-opsin genes

Background  

PCR-based surveys have shown that guppies (Poecilia reticulata) have an unusually large visual-opsin gene repertoire. This has led to speculation that opsin duplication and divergence has enhanced the evolution of elaborate male coloration because it improves spectral sensitivity and/or discrimination in females. However, this conjecture on evolutionary connections between opsin repertoire, vision, mate choice, and male coloration was generated with little data on gene expression. Here, we used RT-qPCR to survey visual-opsin gene expression in the eyes of males, females, and juveniles in order to further understand color-based sexual selection from the perspective of the visual system.     

Determinants for nasal trigeminal detection of volatile organic compounds

We explored the influence of methodological and chemical parameters on the detection of nasal chemesthesis (i.e., trigeminal stimulation) evoked by volatile organic compounds (VOCs). To avoid odor biases, chemesthesis was probed via nasal pungency detection in anosmics and via nasal localization (i.e., lateralization) in normosmics, in both cases using forced-choice procedures. In the experiments with anosmics, 12 neat VOCs were selected based on previous reports of lack of chemesthetic response. Although none of the VOCs reached 100% detection, detectability and confidence of detection were higher when using a glass vessel system adapted with nosepieces to fit the nostrils tightly than when using wide-mouth glass jars. Half the stimuli were detected well above chance and half were not. When the latter were tested again after being heated to 37 degrees C, that is, body temperature (from room temperature, 23 degrees C), to increase their vapor concentration, only one, octane, significantly increased its detectability. Chemesthesis gauged with normosmics mirrored that with anosmics. Gas chromatography measurements showed that, even at 23 degrees C, the saturated vapor concentrations of the undetected stimuli, except vanillin, were well above the respective calculated nasal pungency threshold (NPT) from an equation that, in the past, had accurately described and predicted NPTs. We conclude that, except for octane and perhaps vanillin, the failure of the other four VOCs to precipitate nasal chemesthesis rests on a chemical-structural limitation, for example, the molecules lack a key property to fit a receptor pocket, rather than on a concentration limitation, for example, the vapor concentration is too low to reach a threshold value.     

Comparative agonist/antagonist responses in mutant human C5a receptors define the ligand binding site

The C terminus is responsible for all of the agonist activity of C5a at human C5a receptors (C5aRs). In this report we have mapped the ligand binding site on the C5aR using a series of agonist and antagonist peptide mimics of the C terminus of C5a as well as receptors mutated at putative interaction sites (Ile(116), Arg(175,) Arg(206), Glu(199), Asp(282), and Val(286)). Agonist peptide 1 (Phe-Lys-Pro-d-cyclohexylalanine-cyclohexylalanine-d-Arg) can be converted to an antagonist by substituting the bulkier Trp for cyclohexylalanine at position 5 (peptide 2). Conversely, mutation of C5aR transmembrane residue Ile(116) to the smaller Ala (I116A) makes the receptor respond to peptide 2 as an agonist (Gerber, B. O., Meng, E. C., Dotsch, V., Baranski, T. J., and Bourne, H. R. (2001) J. Biol. Chem. 276, 3394-3400). However, a potent cyclic hexapeptide antagonist, Phe-cyclo-[Orn-Pro-d-cyclohexylalanine-Trp-Arg] (peptide 3), derived from peptide 2 and which binds to the same receptor site, remains a full antagonist at I116AC5aR. This suggests that although the residue at position 5 might bind near to Ile(116), the latter is not essential for either activation or antagonism. Arg(206) and Arg(175) both appear to interact with the C-terminal carboxylate of C5a agonist peptides, suggesting a dynamic binding mechanism that may be a part of a receptor activation switch. Asp(282) has been previously shown to interact with the side chain of the C-terminal Arg residue, and Glu(199) may also interact with this side chain in both C5a and peptide mimics. Using these interactions to orient NMR-derived ligand structures in the binding site of C5aR, a new model of the interaction between peptide antagonists and the C5aR is presented.     

Genetic inactivation of prohormone convertase (PC1) causes a reduction in cholecystokinin (CCK) levels in the hippocampus, amygdala, pons and medulla in mouse brain that correlates with the degree of colocalization of PC1 and CCK mRNA in these structures in rat brain

Prohormone convertase (PC1) is found in endocrine cell lines that express cholecystokinin (CCK) mRNA and process pro CCK to biologically active products. Other studies have demonstrated that PC1 may be a one of the enzymes responsible for the endoproteolytic cleavages that occur in pro CCK during its biosynthesis and processing. Prohormone convertase 1 (PC1) has a distribution that is similar to cholecystokinin (CCK) in rat brain. A moderate to high percentage of CCK mRNA-positive neurons express PC1 mRNA. CCK levels were measured in PC1 knockout and control mice to assess the degree to which loss of PC1 changed CCK content. CCK levels were decreased 62% in hippocampus, 53% in amygdala and 57% in pons-medulla in PC1 knockout mice as compared to controls. These results are highly correlated with the colocalization of CCK and PC1. The majority of CCK mRNA-positive neurons in the pyramidal cell layer of the hippocampus express PC1 mRNA and greater than 50% of CCK mRNA-positive neurons in several nuclei of the amygdala also express PC1. These results demonstrate that PC1 is important for CCK processing. PC2 and PC5 are also widely colocalized with CCK. It may be that PC2, PC5 or another non-PC enzyme are able to substitute for PC1 and sustain production of some amidated CCK. Together these enzymes may represent a redundant system to insure the production of CCK.     

Editors' Note

Editorial Introduction

Editors' Note     

Advances in the neural bases of orientation and navigation

The ability to locomote in one direction (oriented movement),and the ability to navigate toward a distant goal are relatedbehaviors that are phylogenetically widespread. Orientationbehaviors include finding the source of an odor or acousticsignal, using a sun-compass for guidance, and moving relativeto fluid-dynamic cues. Such abilities might require little morethan directionally selective sensors coupled to a turning mechanism.This type of behavior, therefore, can be implemented by relativelysimple circuits. In contrast, navigation involves both the abilityto detect direction, as well as a map-sense that provides position.Navigation is less common and arguably requires greater braincomputation than does simple orientation, but may be presentin arthropods as well as in vertebrates. Great progress hasbeen made in exploring the biophysical and sensory bases forthese behaviors, and in recent years the locations and the identityof the cellular transducers of the sensory stimuli (for example,geomagnetic fields) have been narrowed in some taxa. Similarly,neurons within the central nervous that most likely functionin higher order computational processes have been identified.For example, direction-selective and position-responsive braincells have been located in the brains of mammals and birds,and these cells might contribute to a cognitive map that canenable navigation. One model organism in which orientation andnavigation has been extensively studied is the sea slug Tritoniadiomedea. This animal orients its crawling to chemical, hydrodynamic,and geomagnetic cues. The brain of Tritonia has 7000 relativelylarge neurons that facilitate circuit analysis. Recent workhas characterized both peripheral and central neural correlatesof orientation signals, as well as the control of thrust andturning, and studies of their field behavior have suggestedhow these disparate orientation systems may be integrated. Thesefindings provide the basis for future studies to determine howthe nervous system combines multiple sensory cues into a complexhierarchy of signals that can direct motor output and thereforeguide navigational tasks.     

A new mouse model for autosomal recessive polycystic kidney disease

In the course of large-scale mutagenesis studies, we discovered a mutant that provides a new mouse model for human autosomal recessive polycystic kidney disease. Animals homozygous for this mutation, T(2;10)67Gso, present evidence of grossly cystic renal and hepatic tissue at birth and a limited survival time of 3-4 days. The recessively expressed phenotype is associated with inheritance of a reciprocal translocation involving mouse chromosomes 2 and 10. Here we describe the pathology and phenotype of this new mutation. The mapping of the chromosomal breakpoint to the 1.0-cM critical region defined for another mouse autosomal recessive polycystic kidney disease model, juvenile congenital polycystic kidney disease (jcpk), led us to undertake the complementation testing that confirmed T(2;10)67Gso and jcpk are allelic. Because of the strong resemblance between the phenotype associated with these mouse mutations and early childhood polycystic kidney disease, and because of advantages offered by reciprocal translocations for gene mapping and cloning, T(2;10)67Gso should prove a valuable asset for studies concerning this fatal disease.     

Spatial ecology of wolverines at the southern periphery of distribution

Wolverines (Gulo gulo) in the conterminous United States have experienced range contraction, are uncommon, and have been designated as warranted for protection under the United States Endangered Species Act. Data from the southern edge of the wolverine's circumpolar distribution is sparse, and development of effective conservation strategies would benefit from a more complete understanding of the species' ecology. We captured and radio-monitored 30 wolverines in the Greater Yellowstone Ecosystem (GYE), tested for seasonal habitat selection by elevation band, and examined a suite of spatial characteristics to clarify our understanding of the wolverine's niche. Wolverines in GYE selected for areas >2,600 m latitude-adjusted elevation (LAE; n = 2,257 wolverine locations [12 F, 6 M]). Wolverines avoided areas <2,150 m LAE, including during winter when the vast majority of ungulates are pushed to these elevations by deep snow. Wolverine home ranges were large relative to body size, averaging 303 km² for adult females and 797 km² for adult males (n = 13 [8 F, 5 M] and 33 wolverine-years). Resident adults fit with Global Positioning System (GPS) collars used an area >75% the size of their multi-year home range in an average of 32 days (n = 7 [5 F, 2 M]). Average movement rates of 1.3 km/2-hr indicated that both sexes move distances equivalent to the diameter of their home range every 2 days or the circumference of their home range in <1 week (n = 1,329 2-hr movements, n = 12 individuals [7 F, 5 M]). This capability for movement, the short time-frame over which home ranges were developed, and a lack of home range overlap by same sex adults ( , 90% CI = 0.0–4.8%, n = 22 pairs) suggested territoriality. We estimated wolverine density to be 3.5/1,000 km² of area >2,150 m LAE (95% CI = 2.8–9.6). Dispersal movements extended to at least 170 km for both sexes (n = 5 F, 2 M). At the southern edge of distribution, where suitable and unsuitable conditions exist in close proximity, wolverines selected high-elevation areas near alpine tree-line where a mix of forest, meadow, and boulder fields were present, deep snow-cover existed during winter, and low temperatures near freezing can occur throughout the year. Persistence in these areas where the growing season is brief requires large home ranges that are regularly patrolled, a social system that provides exclusive access to resources, and low densities. These characteristics, along with low reproductive rates, are prevalent throughout the species range, indicating that wolverines are specialists at exploiting a cold, unproductive niche where interspecific competition is limited. The vulnerability inherent in occupying this unproductive niche was likely influential in previous declines within the conterminous United States and will remain a factor as wolverines encounter modern human influences. Conserving wolverines in the conterminous United States will require collaborative management over a large geographic scale. © 2011 The Wildlife Society.