Hot off the presses! Aug 25 Curr Biol

The Aug 25 issue of the Curr Biol is now up on Pubget (About Curr Biol): if you're at a subscribing institution, just click the link in the latest link at the home page. (Note you'll only be able to get all the PDFs in the issue if your institution subscribes to Pubget.)

Latest Articles Include:

• Report spotlight on organic food
  - Curr Biol 19(16):R667-R668 (2009)
  Mediawatch: An official report in Britain claiming no health benefits to organic food sparked questions about the report's remit and a wider agenda. Bernard Dixon reports.
• Malaria's primate links
  - Curr Biol 19(16):R668-R669 (2009)
  New evidence suggests that the parasite responsible for the most lethal form of human malaria jumped from chimpanzees just once. Nigel Williams reports.
• New structural insights
  - Curr Biol 19(16):R669-R670 (2009)
  A signature from Vladimir Putin has finally secured the construction of a revolutionary new European X-ray research facility. Michael Gross reports.
• Basking to attention
  - Curr Biol 19(16):R671-R672 (2009)
  Researchers are increasingly concerned that the needs of sharks be included in future marine conservation plans. Nigel Williams reports.
• John C. Avise
  - Curr Biol 19(16):R673-R674 (2009)
  
• Scale models
  - Curr Biol 19(16):R675 (2009)
  
• Rad52
  - Curr Biol 19(16):R676-R677 (2009)
  
• Fish immunology
  - Curr Biol 19(16):R678-R682 (2009)
  
• Notch Signalling: Receptor cis-Inhibition To Achieve Directionality
  - Curr Biol 19(16):R683-R684 (2009)
  Lateral inhibition, by which single cells become distinct from their neighbours, can be mediated by Notch signalling during animal development. Signalling directionality is presumably achieved by downregulation of the Notch ligand in signal-receiving cells. New evidence suggests that cis-inhibition of the receptor in the ligand-sending cell might also provide directionality.
• Seasonal Biology: Avian Photoreception Goes Deep
  - Curr Biol 19(16):R685-R687 (2009)
  The avian hypothalamus senses light directly, allowing endocrine physiology to synchronise to seasonal day-length changes. New data implicate the photopigment VA-opsin in this deep brain photoreception.
• Müllerian Mimicry: Sharing the Load Reduces the Legwork
  - Curr Biol 19(16):R687-R689 (2009)
  Color pattern mimicry has long been held up as a powerful example of natural selection. A recent study supports the theory by describing Müllerian mimicry rings in Appalachian millipedes that are analogous to those observed in tropical butterflies.
• Microbial Interactions: Bacteria Talk to (Some of) Their Neighbors
  - Curr Biol 19(16):R689-R691 (2009)
  A recent study reports that Bacillus subtilis biofilm formation depends upon paracrine signaling where the signal-producing and target-responsive cells are different.
• Visual Perception: Larger Is Faster
  - Curr Biol 19(16):R691-R693 (2009)
  A recent study has shown that neurons in the inferior temporal cortex of the macaque monkey brain show earlier selectivity to global and large shapes than to local and small ones, which may underlie the faster behavioral responses to global aspects of a scene.
• Behavioural Ecology: Noise Annoys at Community Level
  - Curr Biol 19(16):R693-R695 (2009)
  A new study on the impact of anthropogenic noise on birds takes a behavioural discipline to the level of community ecology: noise can not only harm individual species but also alter species relationships.
• Circadian Biology: A Neuropeptide Is Bound To Activate Its Receptor
  - Curr Biol 19(16):R696-R697 (2009)
  How do circadian pacemaker neurons provide timekeeping signals by which daily rhythms are organized? Recent technological innovations in the fruitfly model system have allowed observations which suggest some important synchronizing signals may themselves not be gated.
• Escape Behaviour: Reciprocal Inhibition Ensures Effective Escape Trajectory
  - Curr Biol 19(16):R697-R699 (2009)
  When a zebrafish makes a fast escape response, Mauthner cells directly activate contralateral spinal interneurons which feed reciprocal inhibition to motorneurons on the stimulated side. Ablation of these interneurons in transgenic animals impairs escape responses, indicating their crucial role in survival.
• Olfactory Information Processing in Drosophila
  - Curr Biol 19(16):R700-R713 (2009)
  In both insect and vertebrate olfactory systems only two synapses separate the sensory periphery from brain areas required for memory formation and the organisation of behaviour. In the Drosophila olfactory system, which is anatomically very similar to its vertebrate counterpart, there has been substantial recent progress in understanding the flow of information from experiments using molecular genetic, electrophysiological and optical imaging techniques. In this review, we shall focus on how olfactory information is processed and transformed in order to extract behaviourally relevant information. We follow the progress from olfactory receptor neurons, through the first processing area, the antennal lobe, to higher olfactory centres. We address both the underlying anatomy and mechanisms that govern the transformation of neural activity. We emphasise our emerging understanding of how different elementary computations, including signal averaging, gain control, decorrelati on and integration, may be mapped onto different circuit elements.
• hunchback Functions as a Segmentation Gene in the Spider Achaearanea tepidariorum
  Schwager EE Pechmann M Feitosa NM McGregor AP Damen WG - Curr Biol 19(16):1333-1340 (2009)
  Background In insects, the gap gene hunchback (hb) is required for the formation of a set of adjacent segments through the regulation of downstream target genes of the pair rule and segment-polarity classes. In addition, hb is a major regulator of Hox genes and it has been suggested that this is the ancestral role of hb in insects or perhaps even arthropods. To date, however, hb function has been analyzed only in insects. Results Here we show that hb acts as a segmentation gene during anterior patterning of a noninsect arthropod, the spider Achaearanea tepidariorum. The leg-bearing segments L1, L2, and L4 are missing after downregulation of At-hb via RNAi. At-hb is required for the correct organization of target genes in this region of the embryo, suggesting that At-hb acts as a gap gene in the spider. In contrast to insects, hb does not control Hox gene expression in the spider. Furthermore, analysis of twist expression in At-hb knockdown embryos demonstrates that hb is not required for initiating the segmental organization of the mesoderm in the affected region, but only for its maintenance. Conclusions Our findings suggest that hb might have had a segmentation gene function in the arthropod ancestor and contradicts the suggestion that the control of Hox genes is the ancestral role of hb. Anterior spider segmentation thus utilizes a Drosophila-like genetic mode, whereas a vertebrate-like mechanism involving Wnt8 and Notch/Delta signaling is used to pattern posterior segments. These data support the hypothesis that short-germ arthropods employ two distinct mechanisms to segment their anterior and posterior body parts.
• Short- and Long-Term Memory in Drosophila Require cAMP Signaling in Distinct Neuron Types
  - Curr Biol 19(16):1341-1350 (2009)
  Background A common feature of memory and its underlying synaptic plasticity is that each can be dissected into short-lived forms involving modification or trafficking of existing proteins and long-term forms that require new gene expression. An underlying assumption of this cellular view of memory consolidation is that these different mechanisms occur within a single neuron. At the neuroanatomical level, however, different temporal stages of memory can engage distinct neural circuits, a notion that has not been conceptually integrated with the cellular view. Results Here, we investigated this issue in the context of aversive Pavlovian olfactory memory in Drosophila. Previous studies have demonstrated a central role for cAMP signaling in the mushroom body (MB). The Ca2+-responsive adenylyl cyclase RUTABAGA is believed to be a coincidence detector in γ neurons, one of the three principle classes of MB Kenyon cells. We were able to separately restore short-term or long-term memory to a rutabaga mutant with expression of rutabaga in different subsets of MB neurons. Conclusions Our findings suggest a model in which the learning experience initiates two parallel associations: a short-lived trace in MB γ neurons, and a long-lived trace in α/β neurons.
• Mushroom Bodies Regulate Habit Formation in Drosophila
  Brembs B - Curr Biol 19(16):1351-1355 (2009)
  To make good decisions, we evaluate past choices to guide later decisions. In most situations, we have the opportunity to simultaneously learn about both the consequences of our choice (i.e., operantly) and the stimuli associated with correct or incorrect choices (i.e., classically) [1]. Interestingly, in many species, including humans, these learning processes occasionally lead to irrational decisions [2]. An extreme case is the habitual drug user consistently administering the drug despite the negative consequences, but we all have experience with our own, less severe habits. The standard animal model employs a combination of operant and classical learning components to bring about habit formation in rodents [3] and [4]. After extended training, these animals will press a lever even if the outcome associated with lever-pressing is no longer desired [5]. In this study, experiments with wild-type and transgenic flies revealed that a prominent insect neuropil, the mushro om bodies (MBs), regulates habit formation in flies by inhibiting the operant learning system when a predictive stimulus is present. This inhibition enables generalization of the classical memory and prevents premature habit formation. Extended training in wild-type flies produced a phenocopy of MB-impaired flies, such that generalization was abolished and goal-directed actions were transformed into habitual responses.
• Attention Narrows Position Tuning of Population Responses in V1
  Fischer J Whitney D - Curr Biol 19(16):1356-1361 (2009)
  When attention is directed to a region of space, visual resolution at that location flexibly adapts, becoming sharper to resolve fine-scale details or coarser to reflect large-scale texture and surface properties [1]. By what mechanism does attention improve spatial resolution? An improved signal-to-noise ratio (SNR) at the attended location contributes [2], because of retinotopically specific signal gain [3], [4], [5], [6], [7], [8], [9] and [10]. Additionally, attention could sharpen position tuning at the neural population level, so that adjacent objects activate more distinct regions of the visual cortex. A dual mechanism involving both signal gain and sharpened position tuning would be highly efficient at improving visual resolution, but there is no direct evidence that attention can narrow the position tuning of population responses. Here, we compared the spatial spread of the fMRI BOLD response for attended versus ignored stimuli. The activity produced by adjacen t stimuli overlapped less when subjects were attending at their locations versus attending elsewhere, despite a stronger peak response with attention. Our results show that even as early as primary visual cortex (V1), spatially directed attention narrows the tuning of population-coded position representations.
• The Multipurpose 15-Protofilament Microtubules in C. elegans Have Specific Roles in Mechanosensation
  Bounoutas A O'Hagan R Chalfie M - Curr Biol 19(16):1362-1367 (2009)
  Because microtubules perform many essential functions in neurons, delineating unique roles attributable to these organelles presents a formidable challenge. Microtubules endow neurons with shape and structure and are required for developmental processes including neurite outgrowth [1], intracellular transport [2], and synapse formation and plasticity [3] and [4]; microtubules in sensory neurons may be required for the above processes in addition to a specific sensory function. In Caenorhabditis elegans, six touch receptor neurons (TRNs) sense gentle touch [5] and uniquely contain 15-protofilament microtubules [6]. Disruption of these microtubules by loss of either the MEC-7 β-tubulin [7] or MEC-12 α-tubulin [8] or by growth in 1 mM colchicine causes touch insensitivity [5] and [6], altered distribution of the touch transduction channel, and a general reduction in protein levels. We show that the effect on touch sensitivity can be separated from the others; microtubule depolymerization in mature TRNs causes touch insensitivity but does not result in protein distribution and production defects. In addition, the mec-12(e1605) mutation selectively causes touch insensitivity without affecting microtubule formation and other cellular processes. Touching e1605 animals produces a reduced mechanoreceptor current that inactivates more rapidly than in wild-type, suggesting a specific role of the microtubules in mechanotransduction.
• Orchid Mimics Honey Bee Alarm Pheromone in Order to Attract Hornets for Pollination
  - Curr Biol 19(16):1368-1372 (2009)
  Approximately one-third of the world's estimated 30,000 orchid species are deceptive and do not reward their pollinators with nectar or pollen [1]. Most of these deceptive orchids imitate the scent of rewarding flowers or potential mates [2] and [3]. In this study, we investigated the floral scent involved in pollinator attraction to the rewardless orchid Dendrobium sinense, a species endemic to the Chinese island Hainan that is pollinated by the hornet Vespa bicolor. Via chemical analyses and electrophysiological methods, we demonstrate that the flowers of D. sinense produce (Z)-11-eicosen-1-ol and that the pollinator can smell this compound. This is a major compound in the alarm pheromones of both Asian (Apis cerana) and European (Apis mellifera) honey bees [4] and [5] and is also exploited by the European beewolf (Philanthus triangulum) to locate its prey [6]. This is the first time that (Z)-11-eicosen-1-ol has been identified as a floral volatile. In behavioral expe riments, we demonstrate that the floral scent of D. sinense and synthetic (Z)-11-eicosen-1-ol are both attractive to hornets. Because hornets frequently capture honey bees to feed to their larvae, we suggest that the flowers of D. sinense mimic the alarm pheromone of honey bees in order to attract prey-hunting hornets for pollination.
• Quantification of Social Behavior in D. discoideum Reveals Complex Fixed and Facultative Strategies
  Buttery NJ Rozen DE Wolf JB Thompson CR - Curr Biol 19(16):1373-1377 (2009)
  Understanding the maintenance of cooperation requires an understanding of the nature of cheaters and the strategies used to mitigate their effects. However, it is often difficult to determine how cheating or differential social success has arisen. For example, cheaters may employ different strategies (e.g., fixed and facultative), whereas other causes of unequal fitness in social situations can result in winners and losers without cheating. To address these problems, we quantified the social success of naturally occurring genotypes of Dictyostelium discoideum during the formation of chimeric fruiting bodies, consisting of dead stalk cells and viable spores. We demonstrate that an apparent competitive dominance hierarchy of spore formation in chimera is partly due to a fixed strategy where genotypes exhibit dramatically different spore allocations. However, we also find complex, variable facultative strategies, where genotypes change their allocation in chimera. By deter mining the magnitude and direction of these changes, we partition facultative cheating into two forms: (1) promotion of individual fitness through selfish behaviour ("self-promotion") and (2) coercion of other genotypes to act cooperatively. Our results demonstrate and define social interactions between D. discoideum isolates, thus providing a conceptual framework for the study of the genetic mechanisms that underpin social evolution.
• cis-Inhibition of Notch by Endogenous Delta Biases the Outcome of Lateral Inhibition
  Miller AC Lyons EL Herman TG - Curr Biol 19(16):1378-1383 (2009)
  Lateral inhibition mediated by Delta/Notch (Dl/N) signaling is used throughout development to limit the number of initially equivalent cells that adopt a particular fate [1], [2] and [3]. Although adjacent cells express both Dl ligand and N receptor, signaling between them ultimately occurs in only one direction. Classically, this has been explained entirely by feedback: activated N can downregulate Dl, amplifying even slight asymmetries in the Dl or N activities of adjacent cells [1], [2], [3], [4] and [5]. Here, however, we present an example of lateral inhibition in which unidirectional signaling depends instead on Dl's ability to inhibit N within the same cell, a phenomenon known as cis-inhibition [6], [7], [8], [9], [10] and [11]. By genetically manipulating individual R1/R6/R7 photoreceptor precursors in the Drosophila eye, we show that loss of Dl-mediated cis-inhibition reverses the direction of lateral signaling. Based on our finding that Dl in R1/R6s requires e ndocytosis to trans-activate but not to cis-inhibit N, we reexamine previously published data from other examples of lateral inhibition. We conclude that cis-inhibition generally influences the direction of Dl/N signaling and should therefore be included in standard models of lateral inhibition.
• A Robust Network of Double-Strand Break Repair Pathways Governs Genome Integrity during C. elegans Development
  - Curr Biol 19(16):1384-1388 (2009)
  To preserve genomic integrity, various mechanisms have evolved to repair DNA double-strand breaks (DSBs) [1]. Depending on cell type or cell cycle phase, DSBs can be repaired error-free, by homologous recombination, or with concomitant loss of sequence information, via nonhomologous end-joining (NHEJ) or single-strand annealing (SSA) [2]. Here, we created a transgenic reporter system in C. elegans to investigate the relative contribution of these pathways in somatic cells during animal development. Although all three canonical pathways contribute to repair in the soma, in their combined absence, animals develop without growth delay and chromosomal breaks are still efficiently repaired. This residual repair, which we call alternative end-joining, dominates DSB repair only in the absence of NHEJ and resembles SSA, but acts independent of the SSA nuclease XPF and repair proteins from other pathways. The dynamic interplay between repair pathways might be developmentally reg ulated, because it was lost from terminally differentiated cells in adult animals. Our results demonstrate profound versatility in DSB repair pathways for somatic cells of C. elegans, which are thus extremely fit to deal with chromosomal breaks.
• Integration of Single and Multicellular Wound Responses
  Clark AG Miller AL Vaughan E Yu HY Penkert R Bement WM - Curr Biol 19(16):1389-1395 (2009)
  Single cells and multicellular tissues rapidly heal wounds. These processes are considered distinct, but one mode of healing—Rho GTPase-dependent formation and closure of a purse string of actin filaments (F-actin) and myosin-2 around wounds—occurs in single cells [1] and [2] and in epithelia [3], [4], [5], [6], [7], [8], [9] and [10]. Here, we show that wounding of one cell in Xenopus embryos elicits Rho GTPase activation around the wound and at the nearest cell-cell junctions in the neighbor cells. F-actin and myosin-2 accumulate at the junctions and around the wound itself, and as the resultant actomyosin array closes over the wound site, junctional F-actin and myosin-2 become mechanically integrated with the actin and myosin-2 around the wound, forming a hybrid purse string. When cells are ablated rather than wounded, Rho GTPase activation and F-actin accumulation occur at cell-cell junctions surrounding the ablated cell, and the purse string closes the hole in the epithelium. Elevation of intracellular free calcium, an essential upstream signal for the single-cell wound response [2] and [11], also occurs at the cell-cell contacts and in neighbor cells. Thus, the single and multicellular purse string wound responses represent points on a signaling and mechanical continuum that are integrated by cell-cell junctions.
• VA Opsin-Based Photoreceptors in the Hypothalamus of Birds
  - Curr Biol 19(16):1396-1402 (2009)
  Studies in the 1930s demonstrated that birds possess photoreceptors that are located within the hypothalamus and regulate photoperiodic responses to day length [1] and [2]. Most recently, photoperiod has been shown to alter the activity of the pars tuberalis to release thyrotrophin, which ultimately drives a reproductive response [3] and [4]. Despite these significant findings, the cellular and molecular identity of the hypothalamic photoreceptors has remained a mystery. Action spectra implicated an opsin-based photopigment system [5], but further identification based on rod- or cone-opsin probes failed, suggesting the utilization of a novel opsin [6]. The vertebrate ancient (VA) opsin photopigments were isolated in 1997 [7] and [8] but were thought to have a restricted taxonomic distribution, confined to the agnatha and teleost fish. Here, we report the isolation of VA opsin from chicken and show that the two isoforms spliced from this gene (cVAL and cVA) are capable o f forming functional photopigments. Further, we show that VA opsin is expressed within a population of hypothalamic neurons with extensive projections to the median eminence. These results provide the most complete cellular and molecular description of a deep brain photoreceptor in any vertebrate and strongly implicate VA opsin in mediating the avian photoperiodic response.
• Reprogramming after Chromosome Transfer into Mouse Blastomeres
  - Curr Biol 19(16):1403-1409 (2009)
  It is well known that oocytes can reprogram differentiated cells, allowing animal cloning by nuclear transfer. We have recently shown that fertilized zygotes retain reprogramming activities [1], suggesting that such activities might also persist in cleavage-stage embryos. Here, we used chromosome transplantation techniques to investigate whether the blastomeres of two-cell-stage mouse embryos can reprogram more differentiated cells. When chromosomes from one of the two blastomeres were replaced with the chromosomes of an embryonic or CD4+ T lymphocyte donor cell, we observed nuclear reprogramming and efficient contribution of the manipulated cell to the developing blastocyst. Embryos produced by this method could be used to derive stem cell lines and also developed to term, generating mosaic "cloned" animals. These results demonstrate that blastomeres retain reprogramming activities and support the notion that discarded human preimplantation embryos may be useful re cipients for the production of genetically tailored human embryonic stem cell lines.
• Rooks Use Stones to Raise the Water Level to Reach a Floating Worm
  - Curr Biol 19(16):1410-1414 (2009)
  In Aesop's fable "The Crow and the Pitcher," a thirsty crow uses stones to raise the level of water in a pitcher and quench its thirst. A number of corvids have been found to use tools in the wild [1], [2], [3] and [4], and New Caledonian crows appear to understand the functional properties of tools and solve complex physical problems via causal and analogical reasoning [5], [6], [7], [8], [9], [10] and [11]. The rook, another member of the corvid family that does not appear to use tools in the wild, also appears able to solve non-tool-related problems via similar reasoning [12]. Here, we present evidence that captive rooks are also able to solve a complex problem by using tools. We presented four captive rooks with a problem analogous to Aesop's fable: raising the level of water so that a floating worm moved into reach. All four subjects solved the problem with an appreciation of precisely how many stones were needed. Three subjects also rapidly learned to use larg e stones over small ones, and that sawdust cannot be manipulated in the same manner as water. This behavior demonstrates a flexible ability to use tools, a finding with implications for the evolution of tool use and cognition in animals.
• Noise Pollution Changes Avian Communities and Species Interactions
  Francis CD Ortega CP Cruz A - Curr Biol 19(16):1415-1419 (2009)
  Humans have drastically changed much of the world's acoustic background with anthropogenic sounds that are markedly different in pitch and amplitude than sounds in most natural habitats [1], [2], [3] and [4]. This novel acoustic background may be detrimental for many species, particularly birds [1]. We evaluated conservation concerns that noise limits bird distributions and reduces nesting success via a natural experiment to isolate the effects of noise from confounding stimuli and to control for the effect of noise on observer detection biases [5]. We show that noise alone reduces nesting species richness and leads to different avian communities. Contrary to expectations, noise indirectly facilitates reproductive success of individuals nesting in noisy areas as a result of the disruption of predator-prey interactions. The higher reproductive success for birds within noisy habitats may be a previously unrecognized factor contributing to the success of urban-adapted spec ies and the loss of birds less tolerant of noise. Additionally, our findings suggest that noise can have cascading consequences for communities through altered species interactions. Given that noise pollution is becoming ubiquitous throughout much of the world, knowledge of species-specific responses to noise and the cumulative effects of these novel acoustics may be crucial to understanding and managing human-altered landscapes.