Palaeontological evidence for an Oligocene divergence between Old World monkeys and apes

Nature 497, 7451 (2013). doi:10.1038/nature12161

Authors: Nancy J. Stevens, Erik R. Seiffert, Patrick M. O’Connor, Eric M. Roberts, Mark D. Schmitz, Cornelia Krause, Eric Gorscak, Sifa Ngasala, Tobin L. Hieronymus & Joseph Temu

Apes and Old World monkeys are prominent components of modern African and Asian ecosystems, yet the earliest phases of their evolutionary history have remained largely undocumented. The absence of crown catarrhine fossils older than ∼20 million years (Myr) has stood in stark contrast to molecular divergence estimates of ∼25–30 Myr for the split between Cercopithecoidea (Old World monkeys) and Hominoidea (apes), implying long ghost lineages for both clades. Here we describe the oldest known fossil ‘ape’, represented by a partial mandible preserving dental features that place it with ‘nyanzapithecine’ stem hominoids. Additionally, we report the oldest stem member of the Old World monkey clade, represented by a lower third molar. Both specimens were recovered from a precisely dated 25.2-Myr-old stratum in the Rukwa Rift, a segment of the western branch of the East African Rift in Tanzania. These finds extend the fossil record of apes and Old World monkeys well into the Oligocene epoch of Africa, suggesting a possible link between diversification of crown catarrhines and changes in the African landscape brought about by previously unrecognized tectonic activity in the East African rift system.

Long-term warming restructures Arctic tundra without changing net soil carbon storage

Nature 497, 7451 (2013). doi:10.1038/nature12129

Authors: Seeta A. Sistla, John C. Moore, Rodney T. Simpson, Laura Gough, Gaius R. Shaver & Joshua P. Schimel

High latitudes contain nearly half of global soil carbon, prompting interest in understanding how the Arctic terrestrial carbon balance will respond to rising temperatures. Low temperatures suppress the activity of soil biota, retarding decomposition and nitrogen release, which limits plant and microbial growth. Warming initially accelerates decomposition, increasing nitrogen availability, productivity and woody-plant dominance. However, these responses may be transitory, because coupled abiotic–biotic feedback loops that alter soil-temperature dynamics and change the structure and activity of soil communities, can develop. Here we report the results of a two-decade summer warming experiment in an Alaskan tundra ecosystem. Warming increased plant biomass and woody dominance, indirectly increased winter soil temperature, homogenized the soil trophic structure across horizons and suppressed surface-soil-decomposer activity, but did not change total soil carbon or nitrogen stocks, thereby increasing net ecosystem carbon storage. Notably, the strongest effects were in the mineral horizon, where warming increased decomposer activity and carbon stock: a ‘biotic awakening’ at depth.

Synthetic analog computation in living cells

Nature 497, 7451 (2013). doi:10.1038/nature12148

Authors: Ramiz Daniel, Jacob R. Rubens, Rahul Sarpeshkar & Timothy K. Lu

A central goal of synthetic biology is to achieve multi-signal integration and processing in living cells for diagnostic, therapeutic and biotechnology applications. Digital logic has been used to build small-scale circuits, but other frameworks may be needed for efficient computation in the resource-limited environments of cells. Here we demonstrate that synthetic analog gene circuits can be engineered to execute sophisticated computational functions in living cells using just three transcription factors. Such synthetic analog gene circuits exploit feedback to implement logarithmically linear sensing, addition, ratiometric and power-law computations. The circuits exhibit Weber’s law behaviour as in natural biological systems, operate over a wide dynamic range of up to four orders of magnitude and can be designed to have tunable transfer functions. Our circuits can be composed to implement higher-order functions that are well described by both intricate biochemical models and simple mathematical functions. By exploiting analog building-block functions that are already naturally present in cells, this approach efficiently implements arithmetic operations and complex functions in the logarithmic domain. Such circuits may lead to new applications for synthetic biology and biotechnology that require complex computations with limited parts, need wide-dynamic-range biosensing or would benefit from the fine control of gene expression.

Structural biology: Tiny enzyme uses context to succeed

Nature 497, 7450 (2013). doi:10.1038/nature12245

Authors: Jimin Zheng & Zongchao Jia

How the enzyme diacylglycerol kinase can form membrane anchors and an active site from so few amino-acid residues has long been a mystery. Crystal structures reveal that it gets by with a little help from its friends. See Letter p.521

Crystal structure of the integral membrane diacylglycerol kinase

Nature 497, 7450 (2013). doi:10.1038/nature12179

Authors: Dianfan Li, Joseph A. Lyons, Valerie E. Pye, Lutz Vogeley, David Aragão, Colin P. Kenyon, Syed T. A. Shah, Christine Doherty, Margaret Aherne & Martin Caffrey

Diacylglycerol kinase catalyses the ATP-dependent phosphorylation of diacylglycerol to phosphatidic acid for use in shuttling water-soluble components to membrane-derived oligosaccharide and lipopolysaccharide in the cell envelope of Gram-negative bacteria. For half a century, this 121-residue kinase has served as a model for investigating membrane protein enzymology, folding, assembly and stability. Here we present crystal structures for three functional forms of this unique and paradigmatic kinase, one of which is wild type. These reveal a homo-trimeric enzyme with three transmembrane helices and an amino-terminal amphiphilic helix per monomer. Bound lipid substrate and docked ATP identify the putative active site that is of the composite, shared site type. The crystal structures rationalize extensive biochemical and biophysical data on the enzyme. They are, however, at variance with a published solution NMR model in that domain swapping, a key feature of the solution form, is not observed in the crystal structures.

Macropinocytosis of protein is an amino acid supply route in Ras-transformed cells

Nature 497, 7451 (2013). doi:10.1038/nature12138

Authors: Cosimo Commisso, Shawn M. Davidson, Rengin G. Soydaner-Azeloglu, Seth J. Parker, Jurre J. Kamphorst, Sean Hackett, Elda Grabocka, Michel Nofal, Jeffrey A. Drebin, Craig B. Thompson, Joshua D. Rabinowitz, Christian M. Metallo, Matthew G. Vander Heiden & Dafna Bar-Sagi

Macropinocytosis is a highly conserved endocytic process by which extracellular fluid and its contents are internalized into cells through large, heterogeneous vesicles known as macropinosomes. Oncogenic Ras proteins have been shown to stimulate macropinocytosis but the functional contribution of this uptake mechanism to the transformed phenotype remains unknown. Here we show that Ras-transformed cells use macropinocytosis to transport extracellular protein into the cell. The internalized protein undergoes proteolytic degradation, yielding amino acids including glutamine that can enter central carbon metabolism. Accordingly, the dependence of Ras-transformed cells on free extracellular glutamine for growth can be suppressed by the macropinocytic uptake of protein. Consistent with macropinocytosis representing an important route of nutrient uptake in tumours, its pharmacological inhibition compromises the growth of Ras-transformed pancreatic tumour xenografts. These results identify macropinocytosis as a mechanism by which cancer cells support their unique metabolic needs and point to the possible exploitation of this process in the design of anticancer therapies.

Crystal structure of a nitrate/nitrite exchanger

Nature 497, 7451 (2013). doi:10.1038/nature12139

Authors: Hongjin Zheng, Goragot Wisedchaisri & Tamir Gonen

Mineral nitrogen in nature is often found in the form of nitrate (NO3−). Numerous microorganisms evolved to assimilate nitrate and use it as a major source of mineral nitrogen uptake. Nitrate, which is central in nitrogen metabolism, is first reduced to nitrite (NO2−) through a two-electron reduction reaction. The accumulation of cellular nitrite can be harmful because nitrite can be reduced to the cytotoxic nitric oxide. Instead, nitrite is rapidly removed from the cell by channels and transporters, or reduced to ammonium or dinitrogen through the action of assimilatory enzymes. Despite decades of effort no structure is currently available for any nitrate transport protein and the mechanism by which nitrate is transported remains largely unknown. Here we report the structure of a bacterial nitrate/nitrite transport protein, NarK, from Escherichia coli, with and without substrate. The structures reveal a positively charged substrate-translocation pathway lacking protonatable residues, suggesting that NarK functions as a nitrate/nitrite exchanger and that protons are unlikely to be co-transported. Conserved arginine residues comprise the substrate-binding pocket, which is formed by association of helices from the two halves of NarK. Key residues that are important for substrate recognition and transport are identified and related to extensive mutagenesis and functional studies. We propose that NarK exchanges nitrate for nitrite by a rocker switch mechanism facilitated by inter-domain hydrogen bond networks.

Erratum: Basic amino-acid side chains regulate transmembrane integrin signalling

Nature 497, 7451 (2013). doi:10.1038/nature12196

Authors: Chungho Kim, Thomas Schmidt, Eun-Gyung Cho, Feng Ye, Tobias S. Ulmer & Mark H. Ginsberg

Nature481, 209–213 (2012); doi:10.1038/nature10697The legend to Fig. 1d of this Letter incorrectly referred to “a POPS lipid's amino NH3+ group (blue)”. It should read “a POPC lipid's choline N(CH3)3+

DNA replication: Driving past four-stranded snags

Nature 497, 7450 (2013). doi:10.1038/nature12244

Authors: Sergei M. Mirkin

Unusual DNA structures, such as G-quadruplexes, can stall DNA replication with drastic consequences for the cell. The Pif1 helicase family of enzymes has evolved to disentangle these structures efficiently. See Article p.458

Pif1 family helicases suppress genome instability at G-quadruplex motifs

Nature 497, 7450 (2013). doi:10.1038/nature12149

Authors: Katrin Paeschke, Matthew L. Bochman, P. Daniela Garcia, Petr Cejka, Katherine L. Friedman, Stephen C. Kowalczykowski & Virginia A. Zakian

The Saccharomyces cerevisiae Pif1 helicase is the prototypical member of the Pif1 DNA helicase family, which is conserved from bacteria to humans. Here we show that exceptionally potent G-quadruplex unwinding is conserved among Pif1 helicases. Moreover, Pif1 helicases from organisms separated by more than

Immune surveillance by CD8αα+ skin-resident T cells in human herpes virus infection

Nature 497, 7450 (2013). doi:10.1038/nature12110

Authors: Jia Zhu, Tao Peng, Christine Johnston, Khamsone Phasouk, Angela S. Kask, Alexis Klock, Lei Jin, Kurt Diem, David M. Koelle, Anna Wald, Harlan Robins & Lawrence Corey

Most herpes simplex virus 2 (HSV-2) reactivations in humans are subclinical and associated with rapid expansion and containment of virus. Previous studies have shown that CD8+ T cells persist in genital skin and mucosa at the dermal–epidermal junction (DEJ)—the portal of neuronal release of reactivating virus—for prolonged time periods after herpes lesions are cleared. The phenotype and function of this persistent CD8+ T-cell population remain unknown. Here, using cell-type-specific laser capture microdissection, transcriptional profiling and T-cell antigen receptor β-chain (TCRβ) genotyping on sequential genital skin biopsies, we show that CD8αα+ T cells are the dominant resident population of DEJ CD8+ T cells that persist at the site of previous HSV-2 reactivation. CD8αα+ T cells located at the DEJ lack chemokine-receptor expression required for lymphocyte egress and recirculation, express gene signatures of T-cell activation and antiviral activity, and produce cytolytic granules during clinical and virological quiescent time periods. Sequencing of the TCR β-chain repertoire reveals that the DEJ CD8αα+ T cells are oligoclonal with diverse usage of TCR variable-β genes, which differ from those commonly described for mucosa-associated invariant T cells and natural killer T cells. Dominant clonotypes are shown to overlap among multiple recurrences over a period of two-and-a-half years. Episodes of rapid asymptomatic HSV-2 containment were also associated with a high CD8 effector-to-target ratio and focal enrichment of CD8αα+ T cells. These studies indicate that DEJ CD8αα+ T cells are tissue-resident cells that seem to have a fundamental role in immune surveillance and in initial containment of HSV-2 reactivation in human peripheral tissue. Elicitation of CD8αα+ T cells may be a critical component for developing effective vaccines against skin and mucosal infections.

Sema3A regulates bone-mass accrual through sensory innervations

Nature 497, 7450 (2013). doi:10.1038/nature12115

Authors: Toru Fukuda, Shu Takeda, Ren Xu, Hiroki Ochi, Satoko Sunamura, Tsuyoshi Sato, Shinsuke Shibata, Yutaka Yoshida, Zirong Gu, Ayako Kimura, Chengshan Ma, Cheng Xu, Waka Bando, Koji Fujita, Kenichi Shinomiya, Takashi Hirai, Yoshinori Asou, Mitsuhiro Enomoto, Hideyuki Okano, Atsushi Okawa & Hiroshi Itoh

Semaphorin 3A (Sema3A) is a diffusible axonal chemorepellent that has an important role in axon guidance. Previous studies have demonstrated that Sema3a−/− mice have multiple developmental defects due to abnormal neuronal innervations. Here we show in mice that Sema3A is abundantly expressed in bone, and cell-based assays showed that Sema3A affected osteoblast differentiation in a cell-autonomous fashion. Accordingly, Sema3a−/− mice had a low bone mass due to decreased bone formation. However, osteoblast-specific Sema3A-deficient mice (Sema3acol1−/− and Sema3aosx−/− mice) had normal bone mass, even though the expression of Sema3A in bone was substantially decreased. In contrast, mice lacking Sema3A in neurons (Sema3asynapsin−/− and Sema3anestin−/− mice) had low bone mass, similar to Sema3a−/− mice, indicating that neuron-derived Sema3A is responsible for the observed bone abnormalities independent of the local effect of Sema3A in bone. Indeed, the number of sensory innervations of trabecular bone was significantly decreased in Sema3asynapsin−/− mice, whereas sympathetic innervations of trabecular bone were unchanged. Moreover, ablating sensory nerves decreased bone mass in wild-type mice, whereas it did not reduce the low bone mass in Sema3anestin−/− mice further, supporting the essential role of the sensory nervous system in normal bone homeostasis. Finally, neuronal abnormalities in Sema3a−/− mice, such as olfactory development, were identified in Sema3asynasin−/− mice, demonstrating that neuron-derived Sema3A contributes to the abnormal neural development seen in Sema3a−/− mice, and indicating that Sema3A produced in neurons regulates neural development in an autocrine manner. This study demonstrates that Sema3A regulates bone remodelling indirectly by modulating sensory nerve development, but not directly by acting on osteoblasts.

The microRNA miR-235 couples blast-cell quiescence to the nutritional state

Nature 497, 7450 (2013). doi:10.1038/nature12117

Authors: Hidefumi Kasuga, Masamitsu Fukuyama, Aya Kitazawa, Kenji Kontani & Toshiaki Katada

The coordination of stem- and blast-cell behaviours, such as self-renewal, differentiation and quiescence, with physiological changes underlies growth, regeneration and tissue homeostasis. Germline stem and somatic blast cells in newly hatched Caenorhabditis elegans larvae can suspend postembryonic development, which consists of diverse cellular events such as migration, proliferation and differentiation, until the nutritional state becomes favourable (termed L1 diapause). Although previous studies showed that the insulin/insulin-like growth factor (IGF) signalling (IIS) pathway regulates this developmental quiescence, the detailed mechanism by which the IIS pathway enables these multipotent cells to respond to nutrient availability is unknown. Here we show in C. elegans that the microRNA (miRNA) miR-235, a sole orthologue of mammalian miR-92 from the oncogenic miR-17-92 cluster, acts in the hypodermis and glial cells to arrest postembryonic developmental events in both neuroblasts and mesoblasts. Expression of mir-235 persists during L1 diapause, and decreases upon feeding in a manner dependent on the IIS pathway. Upregulation of one of the miR-235 targets, nhr-91, which encodes an orthologue of mammalian germ cell nuclear factor, is responsible for defects caused by loss of the miRNA. Our findings establish a novel role of a miR-92 orthologue in coupling blast-cell behaviours to the nutritional state.

Lamin A/C and emerin regulate MKL1–SRF activity by modulating actin dynamics

Nature 497, 7450 (2013). doi:10.1038/nature12105

Authors: Chin Yee Ho, Diana E. Jaalouk, Maria K. Vartiainen & Jan Lammerding

Laminopathies, caused by mutations in the LMNA gene encoding the nuclear envelope proteins lamins A and C, represent a diverse group of diseases that include Emery–Dreifuss muscular dystrophy (EDMD), dilated cardiomyopathy (DCM), limb-girdle muscular dystrophy, and Hutchison–Gilford progeria syndrome. Most LMNA mutations affect skeletal and cardiac muscle by mechanisms that remain incompletely understood. Loss of structural function and altered interaction of mutant lamins with (tissue-specific) transcription factors have been proposed to explain the tissue-specific phenotypes. Here we report in mice that lamin-A/C-deficient (Lmna−/−) and LmnaN195K/N195K mutant cells have impaired nuclear translocation and downstream signalling of the mechanosensitive transcription factor megakaryoblastic leukaemia 1 (MKL1), a myocardin family member that is pivotal in cardiac development and function. Altered nucleo-cytoplasmic shuttling of MKL1 was caused by altered actin dynamics in Lmna−/− and LmnaN195K/N195K mutant cells. Ectopic expression of the nuclear envelope protein emerin, which is mislocalized in Lmna mutant cells and also linked to EDMD and DCM, restored MKL1 nuclear translocation and rescued actin dynamics in mutant cells. These findings present a novel mechanism that could provide insight into the disease aetiology for the cardiac phenotype in many laminopathies, whereby lamin A/C and emerin regulate gene expression through modulation of nuclear and cytoskeletal actin polymerization.

Reconfiguration of the proteasome during chaperone-mediated assembly

Nature 497, 7450 (2013). doi:10.1038/nature12123

Authors: Soyeon Park, Xueming Li, Ho Min Kim, Chingakham Ranjit Singh, Geng Tian, Martin A. Hoyt, Scott Lovell, Kevin P. Battaile, Michal Zolkiewski, Philip Coffino, Jeroen Roelofs, Yifan Cheng & Daniel Finley

The proteasomal ATPase ring, comprising Rpt1–Rpt6, associates with the heptameric α-ring of the proteasome core particle (CP) in the mature proteasome, with the Rpt carboxy-terminal tails inserting into pockets of the α-ring. Rpt ring assembly is mediated by four chaperones, each binding a distinct Rpt subunit. Here we report that the base subassembly of the Saccharomyces cerevisiae proteasome, which includes the Rpt ring, forms a high-affinity complex with the CP. This complex is subject to active dissociation by the chaperones Hsm3, Nas6 and Rpn14. Chaperone-mediated dissociation was abrogated by a non-hydrolysable ATP analogue, indicating that chaperone action is coupled to nucleotide hydrolysis by the Rpt ring. Unexpectedly, synthetic Rpt tail peptides bound α-pockets with poor specificity, except for Rpt6, which uniquely bound the α2/α3-pocket. Although the Rpt6 tail is not visualized within an α-pocket in mature proteasomes, it inserts into the α2/α3-pocket in the base–CP complex and is important for complex formation. Thus, the Rpt–CP interface is reconfigured when the lid complex joins the nascent proteasome to form the mature holoenzyme.

Nonsense mutation in the LGR4 gene is associated with several human diseases and other traits

Nature 497, 7450 (2013). doi:10.1038/nature12124

Authors: Unnur Styrkarsdottir, Gudmar Thorleifsson, Patrick Sulem, Daniel F. Gudbjartsson, Asgeir Sigurdsson, Aslaug Jonasdottir, Adalbjorg Jonasdottir, Asmundur Oddsson, Agnar Helgason, Olafur T. Magnusson, G. Bragi Walters, Michael L. Frigge, Hafdis T. Helgadottir, Hrefna Johannsdottir, Kristin Bergsteinsdottir, Margret H. Ogmundsdottir, Jacqueline R. Center, Tuan V. Nguyen, John A. Eisman, Claus Christiansen, Erikur Steingrimsson, Jon G. Jonasson, Laufey Tryggvadottir, Gudmundur I. Eyjolfsson, Asgeir Theodors, Thorvaldur Jonsson, Thorvaldur Ingvarsson, Isleifur Olafsson, Thorunn Rafnar, Augustine Kong, Gunnar Sigurdsson, Gisli Masson, Unnur Thorsteinsdottir & Kari Stefansson

Low bone mineral density (BMD) is used as a parameter of osteoporosis. Genome-wide association studies of BMD have hitherto focused on BMD as a quantitative trait, yielding common variants of small effects that contribute to the population diversity in BMD. Here we use BMD as a dichotomous trait, searching for variants that may have a direct effect on the risk of pathologically low BMD rather than on the regulation of BMD in the healthy population. Through whole-genome sequencing of Icelandic individuals, we found a rare nonsense mutation within the leucine-rich-repeat-containing G-protein-coupled receptor 4 (LGR4) gene (c.376C>T) that is strongly associated with low BMD, and with osteoporotic fractures. This mutation leads to termination of LGR4 at position 126 and fully disrupts its function. The c.376C>T mutation is also associated with electrolyte imbalance, late onset of menarche and reduced testosterone levels, as well as an increased risk of squamous cell carcinoma of the skin and biliary tract cancer. Interestingly, the phenotype of carriers of the c.376C>T mutation overlaps that of Lgr4 mutant mice.

Corticostriatal neurons in auditory cortex drive decisions during auditory discrimination

Nature 497, 7450 (2013). doi:10.1038/nature12077

Authors: Petr Znamenskiy & Anthony M. Zador

The neural pathways by which information about the acoustic world reaches the auditory cortex are well characterized, but how auditory representations are transformed into motor commands is not known. Here we use a perceptual decision-making task in rats to study this transformation. We demonstrate the role of corticostriatal projection neurons in auditory decisions by manipulating the activity of these neurons in rats performing an auditory frequency-discrimination task. Targeted channelrhodopsin-2 (ChR2)-mediated stimulation of corticostriatal neurons during the task biased decisions in the direction predicted by the frequency tuning of the stimulated neurons, whereas archaerhodopsin-3 (Arch)-mediated inactivation biased decisions in the opposite direction. Striatal projections are widespread in cortex and may provide a general mechanism for the control of motor decisions by sensory cortex.

The TLR4 antagonist Eritoran protects mice from lethal influenza infection

Nature 497, 7450 (2013). doi:10.1038/nature12118

Authors: Kari Ann Shirey, Wendy Lai, Alison J. Scott, Michael Lipsky, Pragnesh Mistry, Lioubov M. Pletneva, Christopher L. Karp, Jaclyn McAlees, Theresa L. Gioannini, Jerrold Weiss, Wilbur H. Chen, Robert K. Ernst, Daniel P. Rossignol, Fabian Gusovsky, Jorge C. G. Blanco & Stefanie N. Vogel

There is a pressing need to develop alternatives to annual influenza vaccines and antiviral agents licensed for mitigating influenza infection. Previous studies reported that acute lung injury caused by chemical or microbial insults is secondary to the generation of host-derived, oxidized phospholipid that potently stimulates Toll-like receptor 4 (TLR4)-dependent inflammation. Subsequently, we reported that Tlr4−/− mice are highly refractory to influenza-induced lethality, and proposed that therapeutic antagonism of TLR4 signalling would protect against influenza-induced acute lung injury. Here we report that therapeutic administration of Eritoran (also known as E5564)—a potent, well-tolerated, synthetic TLR4 antagonist—blocks influenza-induced lethality in mice, as well as lung pathology, clinical symptoms, cytokine and oxidized phospholipid expression, and decreases viral titres. CD14 and TLR2 are also required for Eritoran-mediated protection, and CD14 directly binds Eritoran and inhibits ligand binding to MD2. Thus, Eritoran blockade of TLR signalling represents a novel therapeutic approach for inflammation associated with influenza, and possibly other infections.

Specialized filopodia direct long-range transport of SHH during vertebrate tissue patterning

Nature 497, 7451 (2013). doi:10.1038/nature12157

Authors: Timothy A. Sanders, Esther Llagostera & Maria Barna

The ability of signalling proteins to traverse tissues containing tightly packed cells is of fundamental importance for cell specification and tissue development; however, how this is achieved at a cellular level remains poorly understood. For more than a century, the vertebrate limb bud has served as a model for studying cell signalling during embryonic development. Here we optimize single-cell real-time imaging to delineate the cellular mechanisms for how signalling proteins, such as sonic hedgehog (SHH), that possess membrane-bound covalent lipid modifications traverse long distances within the vertebrate limb bud in vivo. By directly imaging SHH ligand production under native regulatory control in chick (Gallus gallus) embryos, our findings show that SHH is unexpectedly produced in the form of a particle that remains associated with the cell via long cytoplasmic extensions that span several cell diameters. We show that these cellular extensions are a specialized class of actin-based filopodia with novel cytoskeletal features that have not been previously described. Notably, particles containing SHH travel along these extensions with a net anterograde movement within the field of SHH cell signalling. We further show that in SHH-responding cells, specific subsets of SHH co-receptors, including cell adhesion molecule downregulated by oncogenes (CDO) and brother of CDO (BOC), actively distribute and co-localize in specific micro-domains within filopodial extensions, far from the cell body. Stabilized interactions are formed between filopodia containing SHH ligand and those containing co-receptors over a long range. These results suggest that contact-mediated release propagated by specialized filopodia contributes to the delivery of SHH at a distance. Together, these studies identify an important mode of communication between cells that considerably extends our understanding of ligand movement and reception during vertebrate tissue patterning.

Non-redundant coding of aversive odours in the main olfactory pathway

Nature 497, 7450 (2013). doi:10.1038/nature12114

Authors: Adam Dewan, Rodrigo Pacifico, Ross Zhan, Dmitry Rinberg & Thomas Bozza

Many species are critically dependent on olfaction for survival. In the main olfactory system of mammals, odours are detected by sensory neurons that express a large repertoire of canonical odorant receptors and a much smaller repertoire of trace amine-associated receptors (TAARs). Odours are encoded in a combinatorial fashion across glomeruli in the main olfactory bulb, with each glomerulus corresponding to a specific receptor. The degree to which individual receptor genes contribute to odour perception is unclear. Here we show that genetic deletion of the olfactory Taar gene family, or even a single Taar gene (Taar4), eliminates the aversion that mice display to low concentrations of volatile amines and to the odour of predator urine. Our findings identify a role for the TAARs in olfaction, namely, in the high-sensitivity detection of innately aversive odours. In addition, our data reveal that aversive amines are represented in a non-redundant fashion, and that individual main olfactory receptor genes can contribute substantially to odour perception.