Spontaneous fluctuations in brain activity observed with functional magnetic resonance imaging

The majority of functional neuroscience studies have focused on the brain's response to a task or stimulus. However, the brain is very active even in the absence of explicit input or output. In this Article we review recent studies examining spontaneous fluctuations in the blood oxygen level dependent (BOLD) signal of functional magnetic resonance imaging as a potentially important and revealing manifestation of spontaneous neuronal activity. Although several challenges remain, these studies have provided insight into the intrinsic functional architecture of the brain, variability in behaviour and potential physiological correlates of neurological and psychiatric disease.     

Myo1c facilitates G-actin transport to the leading edge of migrating endothelial cells

Addition of actin monomer (G-actin) to growing actin filaments (F-actin) at the leading edge generates force for cell locomotion. The polymerization reaction and its regulation have been studied in depth. However, the mechanism responsible for transport of G-actin substrate to the cell front is largely unknown; random diffusion, facilitated transport via myosin II contraction, local synthesis as a result of messenger ribonucleic acid localization, or F-actin turnover all might contribute. By tracking a photoactivatable, nonpolymerizable actin mutant, we show vectorial transport of G-actin in live migrating endothelial cells (ECs). Mass spectrometric analysis identified Myo1c, an unconventional F-actin-binding motor protein, as a major G-actin-interacting protein. The cargo-binding tail domain of Myo1c interacted with G-actin, and the motor domain was required for the transport. Local microinjection of Myo1c promoted G-actin accumulation and plasma membrane ruffling, and Myo1c knockdown confirmed its contribution to G-actin delivery to the leading edge and for cell motility. In addition, there is no obvious requirement for myosin II contractile-based transport of G-actin in ECs. Thus, Myo1c-facilitated G-actin transport might be a critical node for control of cell polarity and motility.     

Analyzing the effects of species gain and loss on ecosystem function using the extended Price equation partition

In nature species richness and composition, as well as the functioning of individual species, all covary along environmental gradients, making it difficult to tease apart their effects on ecosystem function. Here we use a novel extension of the Price equation to partition the causes of functional variation between any two sites sharing at least one species in common. We use the extension to separate effects of species loss from those of species gain; species gain is analogous to migration in evolution. Previous theoretical and empirical studies of biodiversity and ecosystem function fail to distinguish effects of species gain from those of species loss, and so are conceptually incomplete. Application of this approach to data on total plant biomass along an experimental N enrichment gradient leads to novel empirical insights and reveals subtle effects. For instance, effects of species gain are non‐negligible even though enrichment leads to loss of many species and gain of few, and non‐random gain of high‐biomass species reduces the biomass of the persisting species. We also discuss the interpretation of this new approach, which provides a highly‐general partitioning of the factors affecting ecosystem function.     

Design and characterization of novel hybrid antimicrobial peptides based on cecropin A, LL-37 and magainin II

Antimicrobial peptides (AMPs) are a naturally occurring component of the innate immune response of many organisms and can have activity against both Gram-negative and Gram-positive bacterial species. In order to optimize and improve the direct antimicrobial effect of AMPs against a broad spectrum of bacterial species, novel synthetic hybrids were rationally designed from cecropin A, LL-37 and magainin II. AMPs were selected based on their α-helical secondary structure and fragments of these were analyzed and combined in silico to determine which hybrid peptides would form the best amphipathic cationic α-helices. Four hybrid peptides were synthesized (CaLL, CaMA, LLaMA and MALL) and evaluated for direct antimicrobial activity against a range of bacterial species (Bacillus anthracis, Burkholderia cepacia, Francisella tularensis LVS and Yersinia pseudotuberculosis) alongside the original 'parent' AMPs. The hybrid peptides showed greater antimicrobial effects than the parent AMPs (in one case a parent is completely ineffective while a hybrid based on it removes all traces of bacteria by 3h), although they also demonstrated higher hemolytic properties. Modifications were then carried out to the most toxic hybrid AMP (CaLL) to further improve the therapeutic index. Modifications made to the hybrid lowered hemolytic activity and also lowered antimicrobial activity by various degrees. Overall, this work highlights the potential for rational design and synthesis of improved AMPs that have the capability to be used therapeutically for treatment of bacterial infections.     

Late-Stage Maturation of the Rieske Fe/S Protein: Mzm1 Stabilizes Rip1 but Does Not Facilitate Its Translocation by the AAA ATPase Bcs1

The final step in the assembly of the ubiquinol-cytochrome c reductase or bc₁ complex involves the insertion of the Rieske Fe/S cluster protein, Rip1. Maturation of Rip1 occurs within the mitochondrial matrix prior to its translocation across the inner membrane (IM) in a process mediated by the Bcs1 ATPase and subsequent insertion into the bc₁ complex. Here we show that the matrix protein Mzm1 functions as a Rip1 chaperone, stabilizing Rip1 prior to the translocation step. In the absence of Mzm1, Rip1 is prone to either proteolytic degradation or temperature-induced aggregation. A series of Rip1 truncations were engineered to probe motifs necessary for Mzm1 interaction and Bcs1-mediated translocation of Rip1. The Mzm1 interaction with Rip1 persists in Rip1 variants lacking its transmembrane domain or containing only its C-terminal globular Fe/S domain. Replacement of the globular domain of Rip1 with that of the heterologous folded protein Grx3 abrogated Mzm1 interaction; however, appending the C-terminal 30 residues of Rip1 to the Rip1-Grx3 chimera restored Mzm1 interaction. The Rip1-Grx3 chimera and a Rip1 truncation containing only the N-terminal 92 residues each induced stabilization of the bc₁:cytochrome oxidase supercomplex in a Bcs1-dependent manner. However, the Rip1 variants were not stably associated with the supercomplex. The induced supercomplex stabilization by the Rip1 N terminus was independent of Mzm1.     

Dramatic intraspecific differences in migratory routes,stopover sites and wintering areas,revealed using light-level geolocators

Migratory divides are contact zones between breeding populations that use divergent migratory routes and have been described in a variety of species. These divides are of major importance to evolution, ecology and conservation but have been identified using limited band recovery data and/or indirect methods. Data from band recoveries and mitochondrial haplotypes suggested that inland and coastal Swainson''s thrushes (Catharus ustulatus) form a migratory divide in western North America. We attached light-level geolocators to birds at the edges of this contact zone to provide, to our knowledge, the first direct test of a putative divide using data from individual birds over the entire annual cycle. Coastal thrushes migrated along the west coast to Mexico, Guatemala and Honduras. Some of these birds used multiple wintering sites. Inland thrushes migrated across the Rocky Mountains, through central North America to Columbia and Venezuela. These birds migrated longer distances than coastal birds and performed a loop migration, navigating over the Gulf of Mexico in autumn and around this barrier in spring. These findings support the suggestion that divergent migratory behaviour could contribute to reproductive isolation between migrants, advance our understanding of their non-breeding ecology, and are integral to development of detailed conservation strategies for this group.     

The annual cycle of a trans-equatorial Eurasian-African passerine migrant: different spatio-temporal strategies for autumn and spring migration

The small size of the billions of migrating songbirds commuting between temperate breeding sites and the tropics has long prevented the study of the largest part of their annual cycle outside the breeding grounds. Using light-level loggers (geolocators), we recorded the entire annual migratory cycle of the red-backed shrike Lanius collurio, a trans-equatorial Eurasian-African passerine migrant. We tested differences between autumn and spring migration for nine individuals. Duration of migration between breeding and winter sites was significantly longer in autumn (average 96 days) when compared with spring (63 days). This difference was explained by much longer staging periods during autumn (71 days) than spring (9 days). Between staging periods, the birds travelled faster during autumn (356 km d(-1)) than during spring (233 km d(-1)). All birds made a protracted stop (53 days) in Sahelian sub-Sahara on southbound migration. The birds performed a distinct loop migration (22 000 km) where spring distance, including a detour across the Arabian Peninsula, exceeded the autumn distance by 22 per cent. Geographical scatter between routes was particularly narrow in spring, with navigational convergence towards the crossing point from Africa to the Arabian Peninsula. Temporal variation between individuals was relatively constant, while different individuals tended to be consistently early or late at different departure/arrival occasions during the annual cycle. These results demonstrate the existence of fundamentally different spatio-temporal migration strategies used by the birds during autumn and spring migration, and that songbirds may rely on distinct staging areas for completion of their annual cycle, suggesting more sophisticated endogenous control mechanisms than merely clock-and-compass guidance among terrestrial solitary migrants. After a century with metal-ringing, year-round tracking of long-distance migratory songbirds promises further insights into bird migration.     

Predictions of CCR1 chemokine receptor structure and BX 471 antagonist binding followed by experimental validation

A major challenge in the application of structure-based drug design methods to proteins belonging to the superfamily of G protein-coupled receptors (GPCRs) is the paucity of structural information (1). The 19 chemokine receptors, belonging to the Class A family of GPCRs, are important drug targets not only for autoimmune diseases like multiple sclerosis but also for the blockade of human immunodeficiency virus type 1 entry (2). Using the MembStruk computational method (3), we predicted the three-dimensional structure of the human CCR1 receptor. In addition, we predicted the binding site of the small molecule CCR1 antagonist BX 471, which is currently in Phase II clinical trials (4). Based on the predicted antagonist binding site we designed 17 point mutants of CCR1 to validate the predictions. Subsequent competitive ligand binding and chemotaxis experiments with these mutants gave an excellent correlation to these predictions. In particular, we find that Tyr-113 and Tyr-114 on transmembrane domain 3 and Ile-259 on transmembrane 6 contribute significantly to the binding of BX 471. Finally, we used the predicted and validated structure of CCR1 in a virtual screening validation of the Maybridge data base, seeded with selective CCR1 antagonists. The screen identified 63% of CCR1 antagonists in the top 5% of the hits. Our results indicate that rational drug design for GPCR targets is a feasible approach.     

A polarized-light spectroscopy study of interactions of a hairpin polyamide with DNA

We here study the interactions of a polyamide with large DNA, and compare to those of minor groove binder distamycin (DST), including high ligand/DNA binding ratios. Specific as well as nonspecific binding is probed using polarized-light spectroscopy combined with singular value decomposition analysis. Circular and linear dichroism data confirm binding geometries consistent with minor groove binding for both of the ligands. Interestingly, at high and intermediate ligand/DNA ratios the polyamide exhibits no significant sequence discrimination between mixed-sequence (calf thymus) and AT DNA as compared to DST. Each ligand is concluded to exhibit two different binding modes depending upon ligand/DNA ratio and nucleo-base sequence. At high binding ratios, distinct differences between the ligands are observed: circular dichroism spectra exciton effects provide evidence of bimolecular interactions of the polyamide when bound to AT-DNA, whereas no effects are seen with DST or mixed-sequence DNA. Also linear dichroism indicates that a change in binding geometry occurs at high polyamide/AT ratios, and that the effect occurs only with polyamide in contrast to DST. Since the effect is insignificant with DST, or with calf thymus DNA, it is concluded that it relates to the sizes of the ligands and the minor grooves, becoming critical in the limit of crowding.