Hot off the presses! Feb 22 curr biol

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Latest Articles Include:

• New fears over bee declines
  - curr biol 21(4):R137-R139 (2011)
  Around the world, losses of bee colonies and wild pollinators continue. Emerging explanations are complex and call for more research, but the case against systemic pesticides is gaining strength. Michael Gross investigates.
• Neurospora
  - curr biol 21(4):R139-R140 (2011)
  
• Rosie Redfield
  - curr biol 21(4):R141-R142 (2011)
  
• Human voice perception
  - curr biol 21(4):R143-R145 (2011)
  We are all voice experts. First and foremost, we can produce and understand speech, and this makes us a unique species. But in addition to speech perception, we routinely extract from voices a wealth of socially-relevant information in what constitutes a more primitive, and probably more universal, non-linguistic mode of communication. Consider the following example: you are sitting in a plane, and you can hear a conversation in a foreign language in the row behind you. You do not see the speakers' faces, and you cannot understand the speech content because you do not know the language. Yet, an amazing amount of information is available to you. You can evaluate the physical characteristics of the different protagonists, including their gender, approximate age and size, and associate an identity to the different voices. You can form a good idea of the different speaker's mood and affective state, as well as more subtle cues as the perceived attractiveness or dominance o! f the protagonists. In brief, you can form a fairly detailed picture of the type of social interaction unfolding, which a brief glance backwards can on the occasion help refine — sometimes surprisingly so. What are the acoustical cues that carry these different types of vocal information? How does our brain process and analyse this information? Here we briefly review an emerging field and the main tools used in voice perception research.
• Maintaining a memory by transcriptional autoregulation
  - curr biol 21(4):R146-R147 (2011)
  One of the key features of cellular differentiation programs is stability. Although differentiation is reversible in principle, many components of the gene batteries induced upon terminal differentiation are maintained throughout a cell's life. For example, muscle cells continuously express the myosin gene, and GABAergic neurons continuously express genes for GABA synthesis and transport. Maintaining gene expression patterns in the nervous system is a particular challenge given the non-renewing nature and therefore extensive life span of many neuronal cell types.
• Scott's collections help reveal accelerating marine life growth in Antarctica
  - curr biol 21(4):R147-R148 (2011)
  Scott remains famous for coming second to Amundsen in the race for the South Pole and the fatalities on the journey back to base, but scientific effort on his expedition was never sacrificed and set many invaluable physical and biological baselines. Amongst these were collections of benthos, such as the bryozoan Cellarinella nutti, which records environmental information in tree-ring-like growth check lines. We measured the growth of C. nutti in the Ross Sea from museum and new collections and find no trend from 1890–1970 but a rapid increase from the 1990s to present. This reflects coincident increases in regional phytoplankton production. Thus, it is the first evidence that greater surface productivity is being sequestered to the seabed and thus of increasing polar carbon sinks.
• Asymmetric Segregation: The Shape of Things to Come?
  - curr biol 21(4):R149-R151 (2011)
  Yeast mother cells pay a sacrifice during budding: they keep the extrachromosomal rDNA circles (ERCs) so that their buds have a full lifespan ahead. Two new studies indicate that retention of ERCs in mother cells occurs not by tethering to the nuclear periphery but rather by the simple rules of diffusion in a time-limited and complex landscape.
• Animal Evolution: A Soap Opera of Unremarkable Worms
  - curr biol 21(4):R151-R153 (2011)
  Recent phylogenies have suggested that acoelomorph flatworms might provide insights into the nature of the ancestor of bilaterian animals. However, according to new data acoelomorphs might instead be degenerate deuterostomes closely related to Xenoturbella, muddying the waters of early animal evolution.
• Object Vision: A Matter of Principle
  - curr biol 21(4):R153-R155 (2011)
  A new study shows that sparse coding — a principle which elegantly explains neural selectivity in the early visual system — may also explain selectivity in V4, an intermediate visual area implicated in object vision.
• Germline Determination: Don't Mind the P Granules
  - curr biol 21(4):R155-R157 (2011)
  A recently identified novel role for PPTR-1, the regulatory subunit of phosphatase 2A, in P granule segregation challenges the belief that P granules are responsible for determining the germline in Caenorhabditis elegans.
• Cellular Reprogramming: Chromatin Puts On the Brake
  - curr biol 21(4):R157-R159 (2011)
  Directed reprogramming of differentiated cells allows the generation of specific cell types for therapeutics and can provide unexpected insights into development. A recent study demonstrates that efficient reprogramming of Caenorhabditis elegans germ cells into neurons can be achieved by knocking down a histone chaperone gene and ectopic expression of a terminal selector transcription factor.
• Visual Perception: More Than Meets the Eye
  - curr biol 21(4):R159-R161 (2011)
  A recent study shows that objects changing in colour, luminance, size or shape appear to stop changing when they move. These and other compelling illusions provide tantalizing clues about the mechanisms and limitations of object analysis.
• Split Genes: Another Surprise from Giardia
  - curr biol 21(4):R162-R163 (2011)
  Some genes in the candidate early-branching eukaryote Giardia lamblia occur in separate pieces, transcribed from non-contiguous chromosomal locations. The pre-mRNAs from the separate pieces apparently find each other by regions of complementarity and are subsequently spliced together by the spliceosome. Could genes in pieces, transcribed into separate pre-mRNAs, have been an early feature of spliceosomal evolution?
• Circuit Assembly: The Repulsive Side of Lamination
  - curr biol 21(4):R163-R166 (2011)
  Identifying the mechanisms that shape neuronal circuit architecture remains a major challenge. A recent study shows that repulsive signaling between parallel visual pathways helps organize their connections into laminar circuits in the inner retina.
• Genome Evolution: Horizontal Movements in the Fungi
  - curr biol 21(4):R166-R168 (2011)
  Fungi possess robust cell walls and do not engulf prey cells by phagotrophy. As a consequence they are thought to be relatively immune from the invasion of foreign genes. Nonetheless, a growing body of evidence suggests gene transfer has amended the metabolic networks of many fungal species.
• Phospholipid Transport: Sighting a New Face of an Old Friend
  - curr biol 21(4):R168-R169 (2011)
  A recent study now shows that opsin catalyzes rapid movement of phospholipids from one leaflet of a membrane bilayer to the other. This capability illuminates a mechanism for this physiologically important process.
• PAR-4/LKB1 Mobilizes Nonmuscle Myosin through Anillin to Regulate C. elegans Embryonic Polarization and Cytokinesis
  - curr biol 21(4):259-269 (2011)
  Background The serine/threonine kinase LKB1 regulates cell growth and polarity in metazoans, and loss of LKB1 function is implicated in the development of some epithelial cancers. Despite its fundamental role, the mechanism by which LKB1 regulates polarity establishment and/or maintenance is unclear. In the present study, we use the nematode C. elegans to investigate the role of the LKB1 ortholog PAR-4 in actomyosin contractility, a cellular process essential for polarity establishment and cell division in the early embryo. Results Using high-resolution time-lapse imaging of GFP-tagged nonmuscle myosin II (NMY-2), we found that par-4 mutations reduce actomyosin contractility during polarity establishment, leading to the mispositioning of anterior PAR proteins and to defects in contractile ring ingression during cytokinesis. Fluorescence recovery after photobleaching analysis revealed that the mobility of a cortical population of NMY-2 was reduced in par-4 mutants. Interestingly, the contractility defects of par-4 mutants depend on the reciprocal activity of ANI-1 and ANI-2, two C. elegans homologs of the actin cytoskeletal scaffold protein anillin. Conclusion Because loss of PAR-4 promoted inappropriate accumulation of ANI-2 at the cell cortex, we propose that PAR-4 controls C. elegans embryonic polarity by regulating the activity of anillin family scaffold proteins, thus enabling turnover of cortical myosin and efficient actomyosin contractility. This work provides the first description of a cellular mechanism by which PAR-4/LKB1 mediates cell polarization.
• Control of Local Rho GTPase Crosstalk by Abr
  - curr biol 21(4):270-277 (2011)
  Background The Rho GTPases—Rho, Rac, and Cdc42—regulate the dynamics of F-actin (filamentous actin) and myosin-2 with considerable subcellular precision. Consistent with this ability, active Rho and Cdc42 occupy mutually exclusive zones during single-cell wound repair and asymmetric cytokinesis, suggesting the existence of mechanisms for local crosstalk, but how local Rho GTPase crosstalk is controlled is unknown. Results Using a candidate screen approach for Rho GTPase activators (guanine nucleotide exchange factors; GEFs) and Rho GTPase inactivators (GTPase-activating proteins; GAPs), we find that Abr, a protein with both GEF and GAP activity, regulates Rho and Cdc42 during single-cell wound repair. Abr is targeted to the Rho activity zone via active Rho. Within the Rho zone, Abr promotes local Rho activation via its GEF domain and controls local crosstalk via its GAP domain, which limits Cdc42 activity within the Rho zone. Depletion of Abr attenuates Rho activity and wound repair. Conclusions Abr is the first identified Rho GTPase regulator of single-cell wound healing. Its novel mode of targeting by interaction with active Rho allows Abr to rapidly amplify local increases in Rho activity using its GEF domain while its ability to inactivate Cdc42 using its GAP domain results in sharp segregation of the Rho and Cdc42 zones. Similar mechanisms of local Rho GTPase activation and segregation enforcement may be employed in other processes that exhibit local Rho GTPase crosstalk.
• Apoptosis Ensures Spacing Pattern Formation of Drosophila Sensory Organs
  - curr biol 21(4):278-287 (2011)
  Background In both vertebrates and invertebrates, developing organs and tissues must be precisely patterned. One patterning mechanism is Notch/Delta-mediated lateral inhibition. Through the process of lateral inhibition, Drosophila sensory organ precursors (SOPs) are selected and sensory bristles form into a regular pattern. SOP cell fate is determined by high Delta expression and following expression of neurogenic genes like neuralized. SOP selection is spatially and temporally regulated; however, the dynamic process of precise pattern formation is not clearly understood. Results In this study, using live-imaging analysis, we show that the appearance of neuralized-positive cells is random in both timing and position. Excess neuralized-positive cells are produced by developmental errors at several steps preceding and accompanying lateral inhibition. About 20% of the neuralized-positive cells show aberrant cell characteristics and high Notch activation, which not only suppress neural differentiation but also induce caspase-dependent cell death. These cells never develop into sensory organs, nor do they disturb bristle patterning. Conclusions Our study reveals the incidence of developmental errors that produce excess neuralized-positive cells during sensory organ development. Notch activation in neuralized-positive cells determines aberrant cell fate and typically induces caspase-dependent cell death. Apoptosis is utilized as a mechanism to remove cells that start neural differentiation at aberrant positions and timing and to ensure robust spacing pattern formation.
• A Sparse Object Coding Scheme in Area V4
  - curr biol 21(4):288-293 (2011)
  Sparse coding has long been recognized as a primary goal of image transformation in the visual system [[1], [2], [3] and [4]]. Sparse coding in early visual cortex is achieved by abstracting local oriented spatial frequencies [5] and by excitatory/inhibitory surround modulation [6]. Object responses are thought to be sparse at subsequent processing stages [[7] and [8]], but neural mechanisms for higher-level sparsification are not known. Here, convergent results from macaque area V4 neural recording and simulated V4 populations trained on natural object contours suggest that sparse coding is achieved in midlevel visual cortex by emphasizing representation of acute convex and concave curvature. We studied 165 V4 neurons with a random, adaptive stimulus strategy to minimize bias and explore an unlimited range of contour shapes. V4 responses were strongly weighted toward contours containing acute convex or concave curvature. In contrast, the tuning distribution in nonspar! se simulated V4 populations was strongly weighted toward low curvature. But as sparseness constraints increased, the simulated tuning distribution shifted progressively toward more acute convex and concave curvature, matching the neural recording results. These findings indicate a sparse object coding scheme in midlevel visual cortex based on uncommon but diagnostic regions of acute contour curvature.
• A Bmp/Admp Regulatory Circuit Controls Maintenance and Regeneration of Dorsal-Ventral Polarity in Planarians
  - curr biol 21(4):294-299 (2011)
  Animal embryos have diverse anatomy and vary greatly in size. It is therefore remarkable that a common signaling pathway, BMP signaling, controls development of the dorsoventral (DV) axis throughout the Bilateria [[1], [2], [3], [4], [5], [6], [7] and [8]]. In vertebrates, spatially opposed expression of the BMP family proteins Bmp4 and Admp (antidorsalizing morphogenetic protein) can promote restoration of DV pattern following tissue removal [[9], [10] and [11]]. bmp4 orthologs have been identified in all three groups of the Bilateria (deuterostomes, ecdysozoans, and lophotrochozoans) [12]. By contrast, the absence of admp orthologs in ecdysozoans such as Drosophila and C. elegans has suggested that a regulatory circuit of oppositely expressed bmp4 and admp genes represents a deuterostome-specific innovation. Here we describe the existence of spatially opposed bmp and admp expression in a protostome. An admp ortholog (Smed-admp) is expressed ventrally and laterally in! adult Schmidtea mediterranea planarians, opposing the dorsal-pole expression of Smed-bmp4. Smed-admp is required for regeneration following parasagittal amputation. Furthermore, Smed-admp promotes Smed-bmp4 expression and Smed-bmp4 inhibits Smed-admp expression, generating a regulatory circuit that buffers against perturbations of Bmp signaling. These results suggest that a Bmp/Admp regulatory circuit is a central feature of the Bilateria, used broadly for the establishment, maintenance, and regeneration of the DV axis.
• Noggin and Noggin-Like Genes Control Dorsoventral Axis Regeneration in Planarians
  - curr biol 21(4):300-305 (2011)
  Planarians regenerate a whole animal from a small body piece within a few days [[1] and [2]]. Recent studies have shown that the bone morphogenetic protein (BMP) pathway is required to reestablish the dorsoventral (DV) axis [[3], [4] and [5]]. In vertebrates, the specification of the DV axis depends on the coordinated action of a dual organizer defined by BMP and antidorsalizing morphogenetic protein (ADMP) under the control of several factors, including the inhibitors chordin and noggin [6]. Planarians have an expanded noggin family (up to ten members), which have been classified as canonical noggin (nog) and noggin-like (nlg) genes, the latter carrying an insertion within the noggin domain [7]. Here we show that a BMP/ADMP organizer governs DV axis reestablishment during planarian regeneration, highlighting a greater-than-thought conservation of the mechanisms that establish this axis in protostomes and deuterostomes. Also, we report that whereas noggin genes functio! n as canonical BMP inhibitors, the silencing of planarian nlg8 induces ectopic neurogenesis and enhances ventralizing bmp(RNAi) phenotypes. Finally, we show that noggin-like genes are conserved from cnidarian to vertebrates and that both planarian nlg8 and Xenopus nlg ventralize Xenopus embryos when overexpressed. Remarkably, this ventralization is not associated with an increase in SMAD1/5/8 phosphorylation.
• High Spontaneous Rate of Gene Duplication in Caenorhabditis elegans
  - curr biol 21(4):306-310 (2011)
  Gene and genome duplications are the primary source of new genes and novel functions and have played a pivotal role in the evolution of genomic and organismal complexity [[1] and [2]]. The spontaneous rate of gene duplication is a critical parameter for understanding the evolutionary dynamics of gene duplicates; yet few direct empirical estimates exist and differ widely. The presence of a large population of recently derived gene duplicates in sequenced genomes suggests a high rate of spontaneous origin, also evidenced by population genomic studies reporting rampant copy-number polymorphism at the intraspecific level [[3], [4], [5] and [6]]. An analysis of long-term mutation accumulation lines of Caenorhabditis elegans for gene copy-number changes with array comparative genomic hybridization yields the first direct estimate of the genome-wide rate of gene duplication in a multicellular eukaryote. The gene duplication rate in C. elegans is quite high, on the order of 10! −7 duplications/gene/generation. This rate is two orders of magnitude greater than the spontaneous rate of point mutation per nucleotide site in this species and also greatly exceeds an earlier estimate derived from the frequency distribution of extant gene duplicates in the sequenced C. elegans genome.
• Split Introns in the Genome of Giardia intestinalis Are Excised by Spliceosome-Mediated trans-Splicing
  - curr biol 21(4):311-315 (2011)
  Spliceosomal introns are hallmarks of most eukaryotic genomes and are excised from premature mRNAs by a spliceosome that is among the largest, and most complex, molecular machine in cells [1]. The divergent unicellular eukaryote Giardia intestinalis, the causative agent of giardiasis, also possesses spliceosomes, but only four canonical (cis-spliced) introns have been identified in its genome to date [[2], [3] and [4]]. We demonstrate that this organism has a novel form of spliceosome-mediated trans-splicing of split introns that is essential for generating mature mRNAs for at least two important genes: one encoding a heat shock protein 90 (HSP90), which controls the conformation of a suite of cellular proteins [5], and the other encoding a dynein molecular motor protein, involved in the motility of eukaryotic flagella [6]. These split introns have properties that distinguish them from other trans-splicing systems known within eukaryotes, suggesting that Giardia indepe! ndently evolved a unique system to splice split introns.
• The Capsaicin Receptor TRPV1 Is a Crucial Mediator of the Noxious Effects of Mustard Oil
  - curr biol 21(4):316-321 (2011)
  Mustard oil (MO) is a plant-derived irritant that has been extensively used in experimental models to induce pain and inflammation [[1] and [2]]. The noxious effects of MO are currently ascribed to specific activation of the cation channel TRPA1 in nociceptive neurons [[3] and [4]]. In contrast to this view, we show here that the capsaicin receptor TRPV1 has a surprisingly large contribution to aversive and pain responses and visceral irritation induced by MO. Furthermore, we found that this can be explained by previously unknown properties of this compound. First, MO has a bimodal effect on TRPA1, producing current inhibition at millimolar concentrations. Second, it directly and stably activates mouse and human recombinant TRPV1, as well as TRPV1 channels in mouse sensory neurons. Finally, physiological temperatures enhance MO-induced TRPV1 stimulation. Our results refute the dogma that TRPA1 is the sole nocisensor for MO and motivate a revision of the putative roles ! of these channels in models of MO-induced pain and inflammation. We propose that TRPV1 has a generalized role in the detection of irritant botanical defensive traits and in the coevolution of multiple mammalian and plant species.
• Extreme Aggression in Male Squid Induced by a β-MSP-like Pheromone
  - curr biol 21(4):322-327 (2011)
  Male-male aggression is widespread in the animal kingdom and subserves many functions related to the acquisition or retention of resources such as shelter, food, and mates. These functions have been studied widely in the context of sexual selection, yet the proximate mechanisms that trigger or strengthen aggression are not well known for many taxa. Various external sensory cues (visual, audio, chemical) acting alone or in combination stimulate the complex behavioral interactions of fighting behaviors [1]. Here we report the discovery of a 10 kDa protein, termed Loligo β-microseminoprotein (Loligo β-MSP), that immediately and dramatically changes the behavior of male squid from calm swimming and schooling to extreme fighting, even in the absence of females. Females synthesize Loligo β-MSP in their reproductive exocrine glands and embed the protein in the outer tunic of egg capsules, which are deposited on the open sea floor. Males are attracted to the eggs visually, ! but upon touching them and contacting Loligo β-MSP, they immediately escalate into intense physical fighting with any nearby males. Loligo β-MSP is a distant member of the chordate β-microseminoprotein family [2] found in mammalian reproductive secretions, suggesting that this gene family may have taxonomically widespread roles in sexual competition.
• Red and Green Algal Monophyly and Extensive Gene Sharing Found in a Rich Repertoire of Red Algal Genes
  - curr biol 21(4):328-333 (2011)
  The Plantae comprising red, green (including land plants), and glaucophyte algae are postulated to have a single common ancestor that is the founding lineage of photosynthetic eukaryotes [[1] and [2]]. However, recent multiprotein phylogenies provide little [[3] and [4]] or no [[5] and [6]] support for this hypothesis. This may reflect limited complete genome data available for red algae, currently only the highly reduced genome of Cyanidioschyzon merolae [7], a reticulate gene ancestry [5], or variable gene divergence rates that mislead phylogenetic inference [8]. Here, using novel genome data from the mesophilic Porphyridium cruentum and Calliarthron tuberculosum, we analyze 60,000 novel red algal genes to test the monophyly of red + green (RG) algae and their extent of gene sharing with other lineages. Using a gene-by-gene approach, we find an emerging signal of RG monophyly (supported by 50% of the examined protein phylogenies) that increases with the number of dis! tinct phyla and terminal taxa in the analysis. A total of 1,808 phylogenies show evidence of gene sharing between Plantae and other lineages. We demonstrate that a rich mesophilic red algal gene repertoire is crucial for testing controversial issues in eukaryote evolution and for understanding the complex patterns of gene inheritance in protists.
• Rhythmic TMS over Parietal Cortex Links Distinct Brain Frequencies to Global versus Local Visual Processing
  - curr biol 21(4):334-337 (2011)
  Neural networks underlying visual perception exhibit oscillations at different frequencies (e.g., [[1], [2], [3], [4], [5] and [6]]). But how these map onto distinct aspects of visual perception remains elusive. Recent electroencephalography data indicate that theta or beta frequencies at parietal sensors increase in amplitude when conscious perception is dominated by global or local features, respectively, of a reversible visual stimulus [6]. But this provides only correlative, noninterventional evidence. Here we show via transcranial magnetic stimulation (TMS) interventions that short rhythmic bursts of right-parietal TMS at theta or beta frequency can causally benefit processing of global or local levels, respectively, for hierarchical visual stimuli, especially in the context of salient incongruent distractors. This double dissociation between theta and beta TMS reveals distinct causal roles for particular frequencies in processing global versus local visual featur! es.
• PIN Polarity Maintenance by the Cell Wall in Arabidopsis
  - curr biol 21(4):338-343 (2011)
  A central question in developmental biology concerns the mechanism of generation and maintenance of cell polarity, because these processes are essential for many cellular functions and multicellular development [1]. In plants, cell polarity has an additional role in mediating directional transport of the plant hormone auxin that is crucial for multiple developmental processes [[2], [3] and [4]]. In addition, plant cells have a complex extracellular matrix, the cell wall [[5] and [6]], whose role in regulating cellular processes, including cell polarity, is unexplored. We have found that polar distribution of PIN auxin transporters [7] in plant cells is maintained by connections between polar domains at the plasma membrane and the cell wall. Genetic and pharmacological interference with cellulose, the major component of the cell wall, or mechanical interference with the cell wall disrupts these connections and leads to increased lateral diffusion and loss of polar distr! ibution of PIN transporters for the phytohormone auxin. Our results reveal a plant-specific mechanism for cell polarity maintenance and provide a conceptual framework for modulating cell polarity and plant development via endogenous and environmental manipulations of the cellulose-based extracellular matrix.