Unconscious conditioning of pain responses
Visual cues were shown too rapidly for conscious recognition during both conditioning (COND) and testing (TEST).
Studies have shown that an individual’s pain experience can be heightened or diminished by associating a specific cue, such as an image, with pain of high or low intensity. However, it is unclear whether conscious awareness of the cue is required to learn the association. In a study of 49 participants, Karin Jensen et al. (pp. 7863–7867) tested whether unconscious cues affect pain responses by training participants to associate an image with high pain and another image with low pain. To some participants, the images were presented subliminally, or so rapidly that they could not be consciously recognized. Subsequently, the participants were subjected to an intermediate level of pain while being shown one of the two images and asked to rate the pain. As in the previous trials, the images were presented subliminally to some participants. Participants reported increased pain when shown the image associated with high pain and reduced pain when shown the image associated with low pain, regardless of whether or not the images were presented subliminally. The results suggest that people can learn pain tolerance without being consciously aware, and that unconscious cues may affect learning of high-level cognitive processes. — B.D.
Imaging diffusion through the human nail
Structure of human nail revealed using red and green fluorescent dyes.
Treating nail diseases, such as fungal infections, is difficult because the tightly woven keratin network of the nail acts as a barrier to efficient drug delivery. Wing Sin Chiu et al. (pp. 7725–7730) traced the diffusion of three deuterated solvents—water, propylene glycol, and dimethyl sulfoxide—across human nails using stimulated Raman scattering microscopy, which detects intramolecular vibrations at specified frequencies. The authors measured the intensity of the vibrations as functions of time and depth into the nail. Because the bonds in deuterated compounds vibrate at distinct frequencies from compounds containing normal hydrogen, the deuterated solvents could be distinguished from the nondeuterated keratin in the nails. The authors found that water penetrated about 100 μm into the nail after about 30 minutes, whereas the other two solvents penetrated 40–50 μm after approximately 1 day. The results differed sharply from the behavior predicted by a simple model that assumes constant diffusivity, suggesting that diffusivity increases as the nail takes up solvent because the solvent opens up the keratin structure. Consistent with this hypothesis, all three solvents appeared to compromise the integrity of the outer nail. The findings may guide the development of improved drug delivery platforms for treating nail diseases, according to the authors. — B.D.
HIV-1 release from human macrophage reservoirs
The presence of viral reservoirs in T cells and macrophages has so far prevented the complete eradication of HIV-1 from infected individuals. Virus-containing compartments (VCC) in HIV-infected macrophages hide the virus from both the immune system and antiretroviral agents. Francesca Graziano et al. (pp. E3265–E3273) found that extracellular ATP (eATP) triggers the rapid release of infectious HIV-1 virions that had accumulated in the VCC of infected macrophages. eATP is usually released during necrotic cell death or cell stimulation by inflammatory agents, and was able to induce HIV-1 release in both primary human monocyte-derived macrophages and in differentiated chronically infected macrophage-like U1 cells. The authors found that eATP-induced release of virions was not associated with either passive or active cell death and was blocked by the antidepressant imipramine, previously shown to inhibit microvesicle formation. The effect of eATP was also blocked by a specific inhibitor of the P2X7 receptor. The results suggest a role for the P2X7 receptor and the microvesicle pathway in the release of HIV-1 virions from the VCC of infected macrophages, according to the authors. Modulating the P2X7 receptor and the microvesicle pathway might help interfere with HIV-1 reservoirs in macrophages and aid virus eradication in individuals under combination antiretroviral therapy, the authors suggest. — S.R.
14-3-3 and protein export from endoplasmic reticulum
Model of 14-3-3–enabled cargo packaging.
In eukaryotic cells, membrane-spanning proteins are ferried from the endoplasmic reticulum (ER), a labyrinthine sorting station, to various destinations in vesicles studded with a suite of proteins collectively called the cytosolic coat protein complex II (COPII) coat. Kanika Bajaj Pahuja et al. (pp. E3199–E3206) tested whether 14-3-3, a small cytoplasmic protein ubiquitous in eukaryotic cells and implicated in cellular transport, signaling, and death, functions as an accessory in the incorporation of cargo from the ER into COPII-coated vesicles. Using a cell-free assay, the authors found that 14-3-3 acts as an adaptor in packaging SAC1, an enzyme implicated in protein trafficking, cytoskeletal organization, and Lou Gehrig’s disease-related processes, into COPII-coated transport vesicles. A 7-amino acid sequence (RLSNTSP) in the cytoplasmic domain of SAC1 was crucial to its interaction with 14-3-3 and inclusion in the vesicles, with the LS couplet serving as a minimal putative sorting signal for transport. Further, 14-3-3 directly bound to the cytoplasmic protein Sec24, a core component of the COPII coat that helps cluster cargo, and spurred the packaging of SAC1 in a cell-free vesicle budding reaction triggered using recombinant COPII proteins and membranes from a mammalian cell line. Together, the findings suggest a scenario in which 14-3-3 bridges SAC1 with Sec24, clustering the cargo at the site of exit from the ER. — P.N.
Cancer-associated transcription factors
Relatively little is known about how transcription factors regulate gene expression in tumors. To systematically search for cancer-associated transcription factors, Peng Jiang et al. (pp. 7731–7736) developed a computational framework called RABIT (Regression Analysis with Background InTegration), and comprehensively integrated public transcription factor binding profiles with tumor profiling datasets from The Cancer Genome Atlas, a government-led effort to catalog the genetic changes underlying various cancers. RABIT accounts for the effect of tumor confounding factors—such as copy number alteration, DNA methylation, and transcription factor somatic mutation—on transcriptional regulation. RABIT’s predicted transcription factor impact on tumor gene expression was highly consistent with the knowledge from cancer gene databases, and revealed many novel cancer-associated transcription factors. The authors also applied RABIT on RNA-binding protein motifs, and identified a set of RNA-binding proteins that might play important roles in shaping gene expression in tumors. RABIT demonstrated superior performance compared with other state-of-the-art methods, and the authors suggest that the framework could serve as a general platform for finding cancer-associated regulators of gene expression. The study describes a cost-effective and systematic framework for integrating data about gene regulators with tumor profiling data to better understand gene regulation in cancers, according to the authors. — S.R.
Crows’ quantitative abilities
A crow indicates dots on a touchscreen.
Birds demonstrate an ability to quantify numbers of objects despite lacking the six-layered neocortex brain structure implicated in cognition in primates. To explore the neural basis of numerical aptitude in birds, Helen Ditz and Andreas Nieder (pp. 7827–7832) monitored the activity of single neurons in an endbrain region in crows while the crows performed a number-matching task. The authors found that neuronal activity in the nidopallium caudolaterate (NCL) region of the endbrain was tuned to recognize numbers of items, regardless of the items’ sizes or spatial arrangements. Activity levels in NCL neurons correlated positively with number-matching performance. Crows exhibited greater difficulty discriminating between groups of objects with adjacent numbers of items than between groups with increased numerical distance, as well as increasing difficulty discriminating between numbers with a given numerical distance as the overall numerical magnitude increased. Behavioral and neural performance curves, which indicated the number of times the birds identified a displayed number as equivalent to a previously presented sample number, suggested that the crows may represent numbers logarithmically rather than linearly. Behavioral and neuronal representation of numbers in the crow brain reflect similar processes in the primate brain, suggesting that both birds and primates may have independently adopted similar mechanisms to interpret quantity, according to the authors. — P.G.