Feeling by sight or seeing by touch?

We have addressed the role of occipital and somatosensory cortex in a tactile discrimination task. Sight-ed and congenitally blind subjects rated the roughness and distance spacing for a series of raised dot patterns. When judging roughness, intermediate dot spacings were perceived as being the most rough, while distance judgments generated a linear relation. Low-frequency rTMS applied to somatosensory cortex disrupted roughness without affecting distance judgments, while rTMS to occipital cortex disrupted distance but not roughness judgments. We also tested an early blind patient with bilateral occipital cortex damage. Her performance on the roughness determination task was normal; however, she was greatly impaired with distance judgments. The findings suggest a double-dissociation effect in which roughness and distance are primarily processed in somatosensory and occipital cortex, respectively. The differential effect of rTMS on task performance and corroborative clinical evidence suggest that occipital cortex is engaged in tactile tasks requiring fine spatial discrimination.     

Neuronal death induced by nanomolar amyloid β is mediated by primary phagocytosis of neurons by microglia

Alzheimer disease is characterized by neuronal loss and brain plaques of extracellular amyloid β (Aβ), but the means by which Aβ may induce neuronal loss is not entirely clear. Although high concentrations of Aβ (μM) can induce direct toxicity to neurons, we find that low concentration (nM) induce neuronal loss through a microglia-mediated mechanism. In mixed neuronal-glial cultures from rat cerebellum, 250 nM Aβ1-42 (added as monomers, oligomers or fibers) induced about 30% loss of neurons between 2 and 3 days. This neuronal loss occurred without any increase in neuronal apoptosis or necrosis, and no neuronal loss occurred with Aβ42-1. Aβ greatly increased the phagocytic capacity of microglia and induced phosphatidylserine exposure (an "eat-me" signal) on neuronal processes. Blocking exposed phosphatidylserine by adding annexin V or an antibody to phosphatidylserine or inhibiting microglial phagocytosis by adding either cytochalasin D (to block actin polymerization) or cyclo(RGDfV) (to block vitronectin receptors) significantly prevented neuronal loss. Loss of neuronal synapses occurred in parallel with loss of cell bodies and was also prevented by blocking phagocytosis. Inhibition of phagocytosis prevented neuronal loss with no increase in neuronal death, even after 7 days, suggesting that microglial phagocytosis was the primary cause of neuronal death induced by nanomolar Aβ.     

Inactivation of dopamine β-monooxygenase by hydrogen peroxide and by ascorbate

The inactivation of the water-soluble form of bovine adrenal dopamine β-monooxygenase by H₂O₂ and by ascorbate was studied. Inactivation by H₂O₂ was slow for the copper-free apoenzyme, but addition of copper gave a rapid inactivation. The results presented indicate that the enzyme-bound copper during this inactivation catalyzes partial destruction of its own binding site. The reaction orders for the inactivation by H₂O₂ seem to be 1.0 with respect to the enzyme and in the range 0.6 to 0.8 with respect to H₂O₂. The rate of inactivation obtained in the presence of ascorbate increases with addition of copper and is faster than that obtained by similar concentrations of H₂O₂. The data could not, however, be used to decide whether the inactivation by ascorbate was catalyzed by the enzymebound copper. The inactivation reaction in the presence of ascorbate seems to be of first order with respect to ascorbate at ascorbate concentrations less than 40 μm and decreases toward zero as the ascorbate concentration is increased. Experiments with the Cu(I)-chelator, bathocuproine disulfonate, revealed that inactivation led to weaker binding of copper to the protein, and this effect was more pronounced with H₂O₂ than with ascorbate.     

BAFfled by Poxviruses?

Successful viruses engage in a dynamic interplay with their hosts, where both utilize diverse strategies to impose their supremacy. In this issue of Cell Host & Microbe, Wiebe and Traktman describe a novel interaction between vaccinia virus and mammalian cells. A host protein called BAF can bind ectopic cytoplasmic DNA and block viral DNA replication, whereas vaccinia in turn counteracts this inhibition with a virus-encoded serine threonine kinase that inactivates BAF.     

Formation of Three New Trisaccharide-azoxyglycosides by Transglucosylation by Cycad β-Glucosidase

transglucosylation by a β-d-glucosidase from cycad seeds. These azoxyglycosides, named neocycasin H, I, and J, were identified as O-β-d-glucopyranosyl-(1→4)-O-β-d-glucopyranosyl-(l→3)-O-β-d-glucopyranoside of methylazoxymethanol (MAM), O-β-d-glucopyranosyl-(1→3)-[O-β-d-glucopyranosyl-(1→6)]-O-β-d-glucopyranoside of MAM, and O-β-d-glucopyranosyl-(1→3)-[O-β-d-xylopyranosyl-(1→6)]-O-β-d-glucopyranoside of MAM, respectively. On the basis of their structures, the mechanism of the formation of these neocycasins is also discussed.     

Some properties of auditory neuron’s model trained by firing caused by tones modulated by low-frequency noise

In many sensory systems the formation of burst firing can be observed along a way from the periphery to the central nuclei. We investigate the putative transformation of spontaneous activity in the auditory pathway using a neuron model trained by real firing recorded in the auditory nuclei of the frog. The model has 200 separate inputs (neuronal spines). It is supposed that every spine is a coincidence detector. Its output (synaptic potential) sharply increases at emergence of the precisely certain interpulse interval in an input pulse sequence. If the total synaptic potentials excess a threshold, the model generates output spike, which changes weight of all spines according to the simplified Hebb principle. The model was trained by real firing caused in the auditory nuclei of the frog by tones modulated by low-frequency noise in the frequency ranges of 0–15 Hz, 0–50 Hz or 0–150 Hz. After that training the synaptic weights of every spine essentially changed. Thus, along with some increase of weights of spines tuned to boundary frequencies of modulating noise, the most characteristic change was the emphasizing weights of spines tuned to short interpulse intervals. As a result the spontaneous activity passed through the trained model became much more bursting. Efficiency of a signal transmission in model was higher when input spontaneous activity of real cells contains bursts of spikes. Results of modeling are discussed in connection with modern physiological data demonstrating the functional advantage of bursting.     

TGF-beta activation by traction?

Transforming growth factor (TGF)-betas are powerful cytokines that are secreted as inactive (latent) precursors into the extracellular space. To exert their pleiotropic functions, latent TGF-betas require activation. This requisite restricts TGF-beta signaling to tissues that express TGF-beta-activating proteins such as the adhesion molecule alphavbeta6 integrin. Recent work has uncovered the molecular mechanism by which alphavbeta6 integrin activates latent TGF-beta. Latent-TGF-beta-binding protein 1 has been identified as being the major component of this process, and the integrin-interacting region has been mapped to a poorly conserved sequence stretch called the hinge region.     

Weak protein–protein interactions revealed by immiscible filtration assisted by surface tension

Biological mechanisms are often mediated by transient interactions between multiple proteins. The isolation of intact protein complexes is essential to understanding biochemical processes and an important prerequisite for identifying new drug targets and biomarkers. However, low-affinity interactions are often difficult to detect. Here, we use a newly described method called immiscible filtration assisted by surface tension (IFAST) to isolate proteins under defined binding conditions. This method, which gives a near-instantaneous isolation, enables significantly higher recovery of transient complexes compared to current wash-based protocols, which require reequilibration at each of several wash steps, resulting in protein loss. The method moves proteins, or protein complexes, captured on a solid phase through one or more immiscible-phase barriers that efficiently exclude the passage of nonspecific material in a single operation. We use a previously described polyol-responsive monoclonal antibody to investigate the potential of this new method to study protein binding. In addition, difficult-to-isolate complexes involving the biologically and clinically important Wnt signaling pathway were isolated. We anticipate that this simple, rapid method to isolate intact, transient complexes will enable the discoveries of new signaling pathways, biomarkers, and drug targets.     

Vanadium Uptake by Alfalfa Grown in V–Cd-Contaminated Soil by Pot Experiment

In order to characterize uptake of vanadium in alfalfa grown in vanadium–cadmium (Cd)-contaminated soil, 104 soil samples and 94 plant samples were collected from pot experiment. The results showed alfalfa had strong metal adaptability (up to 400 mg kg⁻¹) and high accumulation (up to 3,440.14 mg kg⁻¹) of vanadium. Root had higher contents and better absorption to vanadium than overground part. Moreover, both root and overground part had direct correlation with vanadium in soil, especially with the sum of first three fractions and reducible fraction. With the increasing of vanadium, higher concentration of Cd may inhibit the absorption of vanadium in alfalfa.     

Large-conductance ion channel measured by whole-cell voltage clamp in single cardiac cells: Modulation byβ-adrenergic stimulation and inhibition by octanol

Summary Membrane currents in single cardiac myocytes from adult guinea pigs were studied by means of the patch-clamp technique (whole-cell mode). During spontaneous or caffeine-induced Ca²⁺ release from the sarcoplasmic reticulum openings of a novel ion channel with large unitary conductance (280 pS) can be recorded. The density of these channels and/or its open-state probability are unusually low. On average in the whole-cell mode simultaneous maximum superposition of only four channels is observed. Opening events of this channel require an intracellular Ca²⁺ transient. Activation by [Ca²⁺] _i , however, seems to be indirect; maximum opening activity occurs with a delay of several hundred milliseconds after peak [Ca²⁺] _i . Single-channel activity can be enhanced by a cyclic AMP dependent process via -adrenergic stimulation of a cell. This can also be mimicked by caffeine, most likely via inhibition of phosphodiesterase. Octanol, an inhibitor of gap-junctional coupling in a variety of tissues. causes a concentration-dependent and reversible decrease in single-channel activity. Unitary conductance is not affected by octanol. The low density of these channels in cardiac membranes and their poor selectivity render and role in normal cardiac electrical activity unlikely. A possible relation of the channel to cardiac gap junctions is discussed.     

Dermal fibroblast proliferation is improved by β-catenin overexpression and inhibited by E-cadherin expression

Several recent studies have shown that proteins of the cadherin-catenin complex are not only involved in cell-cell adhesion but also in the proliferation and differentiation processes. For the first time, we investigated the effect of the quantity of cytoplasmic β-catenin on dermal fibroblast proliferation by overexpressing human β-catenin in human dermal fibroblasts. Our results show that dermal fibroblasts overexpressing normal β-catenin or a stabilized β-catenin mutant have a higher growth rate than control fibroblasts. Moreover, when confluence is reached, the number of fibroblasts is increased when the cells overexpress β-catenin suggesting a role for β-catenin in the regulation of contact growth arrest. Finally, by comparing proliferation in normal dermal fibroblasts and dermal fibroblasts expressing E-cadherin we observed a negative regulatory effect of E-cadherin expression on fibroblast proliferation. These data demonstrate the involvement of β-catenin and cadherin in the dermal fibroblast proliferation process and in contact growth arrest.     

HIF-1α Activation by Intermittent Hypoxia Requires NADPH Oxidase Stimulation by Xanthine Oxidase

Hypoxia-inducible factor 1 (HIF-1) mediates many of the systemic and cellular responses to intermittent hypoxia (IH), which is an experimental model that simulates O₂ saturation profiles occurring with recurrent apnea. IH-evoked HIF-1α synthesis and stability are due to increased reactive oxygen species (ROS) generated by NADPH oxidases, especially Nox2. However, the mechanisms by which IH activates Nox2 are not known. We recently reported that IH activates xanthine oxidase (XO) and the resulting increase in ROS elevates intracellular calcium levels. Since Nox2 activation requires increased intracellular calcium levels, we hypothesized XO-mediated calcium signaling contributes to Nox activation by IH. We tested this possibility in rat pheochromocytoma PC12 cells subjected to IH consisting alternating cycles of hypoxia (1.5% O₂ for 30 sec) and normoxia (21% O₂ for 5 min). Kinetic analysis revealed that IH-induced XO preceded Nox activation. Inhibition of XO activity either by allopurinol or by siRNA prevented IH-induced Nox activation, translocation of the cytosolic subunits p47^phox and p67^phox to the plasma membrane and their interaction with gp91^phox. ROS generated by XO also contribute to IH-evoked Nox activation via calcium-dependent protein kinase C stimulation. More importantly, silencing XO blocked IH-induced upregulation of HIF-1α demonstrating that HIF-1α activation by IH requires Nox2 activation by XO.     

Is calpain activity regulated by membranes and autolysis or by calcium and calpastatin?

Although the Ca(2+)-dependent proteinase (calpain) system has been found in every vertebrate cell that has been examined for its presence and has been detected in Drosophila and parasites, the physiological function(s) of this system remains unclear. Calpain activity has been associated with cleavages that alter regulation of various enzyme activities, with remodeling or disassembly of the cell cytoskeleton, and with cleavages of hormone receptors. The mechanism regulating activity of the calpain system in vivo also is unknown. It has been proposed that binding of the calpains to phospholipid in a cell membrane lowers the Ca2+ concentration, [Ca2+], required for the calpains to autolyze, and that autolysis converts an inactive proenzyme into an active protease. Recent studies, however, show that the calpains bind to specific proteins and not to phospholipids, and that binding to cell membranes does not affect the [Ca2+] required for autolysis. It seems likely that calpain activity is regulated by binding of Ca2+ to specific sites on the calpain molecule, with binding to each site eliciting a response (proteolytic activity, calpastatin binding, etc.) specific for that site. Regulation must also involve an, as yet, undiscovered mechanism that increases the affinity of the Ca(2+)-binding sites for Ca2+.