目次

Editorials

科学のための動物実験だとしても、動物の権利を守るべく、最大限の配慮をしなくてはならない。

Failure of care p.187

Laboratory animals must have the very best standard of care if we are to justify their use in science. As one institution is found wanting, others should look to review their animal-welfare practices.

doi: 10.1038/504187a

アクセスの簡便さと透明性の改善が、オープンソースの特許データベースの成功のカギだ。

The patent bargain p.187

An open-source patent database highlights the need for more transparency worldwide.

doi: 10.1038/504187b

Natureの記者や編集者については、女性の割合が増えたものの、レフェリーなどはまだ女性の割合が低く、改善が必要だ。

Gender progress (?) p.188

Despite some success, the proportions of women in Nature’s pages and as referees are still too low.

doi: 10.1038/504188a

News

バナナに重大な被害をもたらす真菌がアフリカや中東で見つかり、南米に広がる懸念も。

Fungus threatens top banana p.195

Fears rise for Latin American industry as devastating disease hits leading variety in Africa and Middle East.

doi: 10.1038/504195a

陥没穴による被害が相次いでいるフロリダ州で、危険性予測地図作成の計画が。

Florida forecasts sinkhole burden p.196

Predictive model will map areas vulnerable to collapse.

doi: 10.1038/504196a

糖尿病治療薬に厳しい安全性が求められており、その認可までの道が険しいものに。

Diabetes drugs ride a bumpy road p.198

Safety worries hamper emerging therapies.

doi: 10.1038/504198a

作物の収量や耐性を高めるため、菌類の力を利用へ。

Food fuelled with fungi p.199

Ecologists are starting to appreciate the power of microbes to make crops hardier.

doi: 10.1038/504199a

インドで、生物多様性に富んだ山岳地域の保護をめぐって、激しい論争が。

India faces uphill battle on biodiversity p.200

Government decision to limit protection for species-rich mountains angers conservationists.

doi: 10.1038/504200a

初期宇宙は暖かく、水や生命は宇宙のごく初期にすでに存在していた可能性があるという説が。

Life possible in the early Universe p.201

Planets orbiting the first stars could have been habitable, challenging arguments for a multiverse.

doi: 10.1038/504201a

News Features

放射性同位体:医学検査の危機

Radioisotopes: The medical testing crisis p.202

医療用の放射性同位体の深刻な供給不足が懸念されており、原子炉を使わずに同位体を作製する方法の研究が続けられている。

doi: 10.1038/504202a

地球科学:火山の下で

Earth science: Under the volcano p.206

大規模噴火の源となるマントルプルームの証拠をつかもうと、地球物理学者たちが探索を試みている。

doi: 10.1038/504206a

News & Views

神経科学:キス・アンド・ランよりずっと速い

Neuroscience: Faster than kiss-and-run p.220

神経接合部で起こる小胞エンドサイトーシスの超高速モードが明らかになった。これは、脳機能を支える重要な過程の1つである。従って、エンドサイトーシスについての以前からある2つのモデルには再評価が必要となりそうだ。

doi: 10.1038/nature12842

太陽系外惑星:ハビタブルゾーンの内側境界

Extrasolar planets: Inner edge of the habitable zone p.221

太陽に似た星で、ハビタブルゾーン(生命居住可能領域)内に岩石惑星を有しているものの割合は、以前に推定されていたよりも少ないらしいことが、三次元気候モデルによって示された。

doi: 10.1038/504221a

発生生物学:胚での機械作用

Developmental biology: Mechanics in the embryo p.223

初期の胚組織の形態を作り出す動きに伴って生じる内在的な機械的ストレスは、細胞運命指定に重要で、進化的に保存された役割を担っていることが示された。

doi: 10.1038/504223a

がん:抑制スイッチ

Cancer: A suppression switch p.225

マウスでは、細胞のオートファジー経路の阻害が膵臓がんの発生を促進するか、あるいは阻害するかを決めているのはp53タンパク質の状態である。この知見は、オートファジー阻害剤の臨床試験について、注意を促すものだ。

doi: 10.1038/nature12841

宇宙物理学:我らの隣人の過去を追跡

Astrophysics: Tracking our neighbours' past p.226

アンドロメダ銀河と天の川銀河を囲む平面内にある矮小銀河の集団的な動きは、理論に疑問を投げかけてきた。はるかな過去の銀河群間の相互作用が、こうした矮小銀河に影響を残したのかもしれない。

doi: 10.1038/504226a

神経科学:記憶形成がアップする時、ダウンする時

Neuroscience: The highs and lows of memory p.228

最近の経験は、記憶に正または負の影響を与えることがある。タンパク質のパルブアルブミンを発現する抑制性ニューロンの小集団が、この過程に重要な役割を持っているらしい。

doi: 10.1038/504228a

ソフトマターの物理学:強磁性流体

Soft-matter physics: Ferromagnetic ferrofluids p.229

強磁性を示す磁性粒子を含む液体を作り出すというアイデアは、これまで実現されたことがなかった。しかし今回、板状磁石を液晶中に置いたものが、こうした性質を示すことが明らかにされた。

doi: 10.1038/504229a

Review

進化:真核生物の起源が古細菌であることは生物の基本的なドメインが2つだけだとする説を裏付ける

An archaeal origin of eukaryotes supports only two primary domains of life p.231

The discovery of the Archaea and the proposal of the three-domains ‘universal’ tree, based on ribosomal RNA and core genes mainly involved in protein translation, catalysed new ideas for cellular evolution and eukaryotic origins. However, accumulating evidence suggests that the three-domains tree may be incorrect: evolutionary trees made using newer methods place eukaryotic core genes within the Archaea, supporting hypotheses in which an archaeon participated in eukaryotic origins by founding the host lineage for the mitochondrial endosymbiont. These results provide support for only two primary domains of life—Archaea and Bacteria—because eukaryotes arose through partnership between them.

doi: 10.1038/nature12779

Articles

材料科学:磁性小板の液晶懸濁液における強磁性

Ferromagnetism in suspensions of magnetic platelets in liquid crystal p.237

The idea that magnetic particles suspended in a liquid crystal might spontaneously orient into a ferromagnetic state has hitherto not been confirmed experimentally, but such a state has now been realized using nanometre-sized ferromagnetic platelets in a nematic liquid crystal.

doi: 10.1038/nature12863

神経科学:マウスの海馬シナプスで起こる超高速エンドサイトーシス

Ultrafast endocytosis at mouse hippocampal synapses p.242

Sustained neurotransmission requires recycling of synaptic vesicles, but the proposed mechanisms have been controversial; here a ‘flash-and-freeze’ method for electron microscopy reveals a new ultrafast form of endocytosis that is actin- and dynamin-dependent and occurs within 100 milliseconds of stimulation.

doi: 10.1038/nature12809

医学:マラリア根絶のためにマラリア原虫のPI(4)Kを標的とする

Targeting Plasmodium PI(4)K to eliminate malaria p.248

The lipid kinase phosphatidylinositol-4-OH kinase (PI(4)K) is identified as a target of the imidazopyrazines, a new antimalarial compound class that can inhibit several Plasmodium species at each stage of the parasite life cycle; the imidazopyrazines exert their inhibitory action by interacting with the ATP-binding pocket of PI(4)K.

doi: 10.1038/nature12782

構造生物学:ヒトGABAB受容体でのリガンドによる活性化の構造的機構

Structural mechanism of ligand activation in human GABAB receptor p.254

Crystallographic structural analysis of bound states of the GBR1 and GBR2 subunits of human GABAB receptor shows that both subunits adopt an open conformation at rest — represented by the apo and antagonist-bound structures — and that only GBR1 closes in the activated state — represented by the agonist-bound structure.

doi: 10.1038/nature12725

Letters

宇宙:恒星質量のブラックホール候補天体4U 1630-47の相対論的ジェットにおけるバリオン物質

Baryons in the relativistic jets of the stellar-mass black-hole candidate 4U 1630-47 p.260

Accreting black holes are known to power relativistic jets, both in stellar-mass binary systems and at the centres of galaxies. The power carried away by the jets, and, hence, the feedback they provide to their surroundings, depends strongly on their composition. Jets containing a baryonic component should carry significantly more energy than electron–positron jets. Energetic considerations and circular-polarization measurements have provided conflicting circumstantial evidence for the presence or absence of baryons in jets, and the only system in which they have been unequivocally detected is the peculiar X-ray binary SS 433 (refs 4, 5). Here we report the detection of Doppler-shifted X-ray emission lines from a more typical black-hole candidate X-ray binary, 4U 1630-47, coincident with the reappearance of radio emission from the jets of the source. We argue that these lines arise from baryonic matter in a jet travelling at approximately two-thirds the speed of light, thereby establishing the presence of baryons in the jet. Such baryonic jets are more likely to be powered by the accretion disk than by the spin of the black hole, and if the baryons can be accelerated to relativistic speeds, the jets should be strong sources of γ-rays and neutrino emission.

doi: 10.1038/nature12672

量子情報科学:厳密に解ける量子通信モデル

An exactly solvable model for quantum communications p.263

Information theory establishes the ultimate limits on performance for noisy communication systems. Accurate models of physical communication devices must include quantum effects, but these typically make the theory intractable. As a result, communication capacities—the maximum possible rates of data transmission—are not known, even for transmission between two users connected by an electromagnetic waveguide with Gaussian noise. Here we present an exactly solvable model of communication with a fully quantum electromagnetic field. This gives explicit expressions for all point-to-point capacities of noisy quantum channels, with implications for quantum key distribution and fibre-optic communications. We also develop a theory of quantum communication networks by solving some rudimentary models including broadcast and multiple-access channels. We compare the predictions of our model with the orthodox Gaussian model and in all cases find agreement to within a few bits. At high signal-to-noise ratios, our simple model captures the relevant physics while remaining amenable to exact solution.

doi: 10.1038/nature12669

惑星科学:地球型惑星における暴走温室効果過程の日射しきい値の増大

Increased insolation threshold for runaway greenhouse processes on Earth-like planets p.268

The increase in solar luminosity over geological timescales should warm the Earth’s climate, increasing water evaporation, which will in turn enhance the atmospheric greenhouse effect. Above a certain critical insolation, this destabilizing greenhouse feedback can ‘run away’ until the oceans have completely evaporated. Through increases in stratospheric humidity, warming may also cause evaporative loss of the oceans to space before the runaway greenhouse state occurs. The critical insolation thresholds for these processes, however, remain uncertain because they have so far been evaluated using one-dimensional models that cannot account for the dynamical and cloud feedback effects that are key stabilizing features of the Earth’s climate. Here we use a three-dimensional global climate model to show that the insolation threshold for the runaway greenhouse state to occur is about 375 W m−2, which is significantly higher than previously thought. Our model is specifically developed to quantify the climate response of Earth-like planets to increased insolation in hot and extremely moist atmospheres. In contrast with previous studies, we find that clouds have a destabilizing feedback effect on the long-term warming. However, subsident, unsaturated regions created by the Hadley circulation have a stabilizing effect that is strong enough to shift the runaway greenhouse limit to higher values of insolation than are inferred from one-dimensional models. Furthermore, because of wavelength-dependent radiative effects, the stratosphere remains sufficiently cold and dry to hamper the escape of atmospheric water, even at large fluxes. This has strong implications for the possibility of liquid water existing on Venus early in its history, and extends the size of the habitable zone around other stars.

doi: 10.1038/nature12827

神経科学:経験で誘導されるパルブアルブミン発現かご細胞ネットワークの可塑性が成体動物の学習を調節する

Parvalbumin-expressing basket-cell network plasticity induced by experience regulates adult learning p.272

Learning and memory processes can be influenced by recent experience, but the mechanisms involved are poorly understood. Enhanced plasticity during critical periods of early life is linked to differentiating parvalbumin (PV)-interneuron networks, suggesting that recent experience may modulate learning by targeting the differentiation state of PV neurons in the adult. Here we show that environmental enrichment and Pavlovian contextual fear conditioning induce opposite, sustained and reversible hippocampal PV-network configurations in adult mice. Specifically, enrichment promotes the emergence of large fractions of low-differentiation (low PV and GAD67 expression) basket cells with low excitatory-to-inhibitory synaptic-density ratios, whereas fear conditioning leads to large fractions of high-differentiation (high PV and GAD67 expression) basket cells with high excitatory-to-inhibitory synaptic-density ratios. Pharmacogenetic inhibition or activation of PV neurons was sufficient to induce such opposite low-PV-network or high-PV-network configurations, respectively. The low-PV-network configuration enhanced structural synaptic plasticity, and memory consolidation and retrieval, whereas these were reduced by the high-PV-network configuration. We then show that maze navigation learning induces a hippocampal low-PV-network configuration paralleled by enhanced memory and structural synaptic plasticity throughout training, followed by a shift to a high-PV-network configuration after learning completion. The shift to a low-PV-network configuration specifically involved increased vasoactive intestinal polypeptide (VIP)-positive GABAergic boutons and synaptic transmission onto PV neurons. Closely comparable low- and high-PV-network configurations involving VIP boutons were specifically induced in primary motor cortex upon rotarod motor learning. These results uncover a network plasticity mechanism induced after learning through VIP–PV microcircuit modulation, and involving large, sustained and reversible shifts in the configuration of PV basket-cell networks in the adult. This novel form of experience-related plasticity in the adult modulates memory consolidation, retrieval and learning, and might be harnessed for therapeutic strategies to promote cognitive enhancement and neuroprotection.

doi: 10.1038/nature12866

細胞:皮膚の発生および修復においては複数の異なる繊維芽細胞系譜が皮膚構造を決める

Distinct fibroblast lineages determine dermal architecture in skin development and repair p.277

Fibroblasts are the major mesenchymal cell type in connective tissue and deposit the collagen and elastic fibres of the extracellular matrix (ECM). Even within a single tissue, fibroblasts exhibit considerable functional diversity, but it is not known whether this reflects the existence of a differentiation hierarchy or is a response to different environmental factors. Here we show, using transplantation assays and lineage tracing in mice, that the fibroblasts of skin connective tissue arise from two distinct lineages. One forms the upper dermis, including the dermal papilla that regulates hair growth and the arrector pili muscle, which controls piloerection. The other forms the lower dermis, including the reticular fibroblasts that synthesize the bulk of the fibrillar ECM, and the preadipocytes and adipocytes of the hypodermis. The upper lineage is required for hair follicle formation. In wounded adult skin, the initial wave of dermal repair is mediated by the lower lineage and upper dermal fibroblasts are recruited only during re-epithelialization. Epidermal β-catenin activation stimulates the expansion of the upper dermal lineage, rendering wounds permissive for hair follicle formation. Our findings explain why wounding is linked to formation of ECM-rich scar tissue that lacks hair follicles. They also form a platform for discovering fibroblast lineages in other tissues and for examining fibroblast changes in ageing and disease.

doi: 10.1038/nature12783

細胞:ヒトの新しい基底状態ナイーブ型多能性幹細胞の誘導

Derivation of novel human ground state naive pluripotent stem cells p.282

Mouse embryonic stem (ES) cells are isolated from the inner cell mass of blastocysts, and can be preserved in vitro in a naive inner-cell-mass-like configuration by providing exogenous stimulation with leukaemia inhibitory factor (LIF) and small molecule inhibition of ERK1/ERK2 and GSK3β signalling (termed 2i/LIF conditions). Hallmarks of naive pluripotency include driving Oct4 (also known as Pou5f1) transcription by its distal enhancer, retaining a pre-inactivation X chromosome state, and global reduction in DNA methylation and in H3K27me3 repressive chromatin mark deposition on developmental regulatory gene promoters. Upon withdrawal of 2i/LIF, naive mouse ES cells can drift towards a primed pluripotent state resembling that of the post-implantation epiblast. Although human ES cells share several molecular features with naive mouse ES cells, they also share a variety of epigenetic properties with primed murine epiblast stem cells (EpiSCs). These include predominant use of the proximal enhancer element to maintain OCT4 expression, pronounced tendency for X chromosome inactivation in most female human ES cells, increase in DNA methylation and prominent deposition of H3K27me3 and bivalent domain acquisition on lineage regulatory genes. The feasibility of establishing human ground state naive pluripotency in vitro with equivalent molecular and functional features to those characterized in mouse ES cells remains to be defined. Here we establish defined conditions that facilitate the derivation of genetically unmodified human naive pluripotent stem cells from already established primed human ES cells, from somatic cells through induced pluripotent stem (iPS) cell reprogramming or directly from blastocysts. The novel naive pluripotent cells validated herein retain molecular characteristics and functional properties that are highly similar to mouse naive ES cells, and distinct from conventional primed human pluripotent cells. This includes competence in the generation of cross-species chimaeric mouse embryos that underwent organogenesis following microinjection of human naive iPS cells into mouse morulas. Collectively, our findings establish new avenues for regenerative medicine, patient-specific iPS cell disease modelling and the study of early human development in vitro and in vivo.

doi: 10.1038/nature12745

微生物学:鞭毛成長の連鎖機構

A chain mechanism for flagellum growth p.287

Bacteria swim by means of long flagella extending from the cell surface. These are assembled from thousands of protein subunits translocated across the cell membrane by an export machinery at the base of each flagellum. Unfolded subunits then transit through a narrow channel at the core of the growing flagellum to the tip, where they crystallize into the nascent structure. As the flagellum lengthens outside the cell, the rate of flagellum growth does not change. The mystery is how subunit transit is maintained at a constant rate without a discernible energy source in the channel of the external flagellum. We present evidence for a simple physical mechanism for flagellum growth that harnesses the entropic force of the unfolded subunits themselves. We show that a subunit docked at the export machinery can be captured by a free subunit through head-to-tail linkage of juxtaposed amino (N)- and carboxy (C)-terminal helices. We propose that sequential rounds of linkage would generate a multisubunit chain that pulls successive subunits into and through the channel to the flagellum tip, and by isolating filaments growing on bacterial cells we reveal the predicted chain of head-to-tail linked subunits in the transit channel of flagella. Thermodynamic analysis confirms that links in the subunit chain can withstand the pulling force generated by rounds of subunit crystallization at the flagellum tip, and polymer theory predicts that as the N terminus of each unfolded subunit crystallizes, the entropic force at the subunit C terminus would increase, rapidly overcoming the threshold required to pull the next subunit from the export machinery. This pulling force would adjust automatically over the increasing length of the growing flagellum, maintaining a constant rate of subunit delivery to the tip.

doi: 10.1038/nature12682

細胞生物学:RNAiを用いたゲノム全体にわたるハイコンテントスクリーニングによる、パーキン遺伝子上流にあるマイトファジー調節因子の同定

High-content genome-wide RNAi screens identify regulators of parkin upstream of mitophagy p.291

An increasing body of evidence points to mitochondrial dysfunction as a contributor to the molecular pathogenesis of neurodegenerative diseases such as Parkinson’s disease. Recent studies of the Parkinson’s disease associated genes PINK1 (ref. 2) and parkin (PARK2, ref. 3) indicate that they may act in a quality control pathway preventing the accumulation of dysfunctional mitochondria. Here we elucidate regulators that have an impact on parkin translocation to damaged mitochondria with genome-wide small interfering RNA (siRNA) screens coupled to high-content microscopy. Screening yielded gene candidates involved in diverse cellular processes that were subsequently validated in low-throughput assays. This led to characterization of TOMM7 as essential for stabilizing PINK1 on the outer mitochondrial membrane following mitochondrial damage. We also discovered that HSPA1L (HSP70 family member) and BAG4 have mutually opposing roles in the regulation of parkin translocation. The screens revealed that SIAH3, found to localize to mitochondria, inhibits PINK1 accumulation after mitochondrial insult, reducing parkin translocation. Overall, our screens provide a rich resource to understand mitochondrial quality control.

doi: 10.1038/nature12748

がん:p53の状態が膵臓がん形成におけるオートファジーの役割を決める

p53 status determines the role of autophagy in pancreatic tumour development p.296

Macroautophagy (hereafter referred to as autophagy) is a process in which organelles termed autophagosomes deliver cytoplasmic constituents to lysosomes for degradation. Autophagy has a major role in cellular homeostasis and has been implicated in various forms of human disease. The role of autophagy in cancer seems to be complex, with reports indicating both pro-tumorigenic and tumour-suppressive roles. Here we show, in a humanized genetically-modified mouse model of pancreatic ductal adenocarcinoma (PDAC), that autophagy’s role in tumour development is intrinsically connected to the status of the tumour suppressor p53. Mice with pancreases containing an activated oncogenic allele of Kras (also called Ki-Ras)—the most common mutational event in PDAC—develop a small number of pre-cancerous lesions that stochastically develop into PDAC over time. However, mice also lacking the essential autophagy genes Atg5 or Atg7 accumulate low-grade, pre-malignant pancreatic intraepithelial neoplasia lesions, but progression to high-grade pancreatic intraepithelial neoplasias and PDAC is blocked. In marked contrast, in mice containing oncogenic Kras and lacking p53, loss of autophagy no longer blocks tumour progression, but actually accelerates tumour onset, with metabolic analysis revealing enhanced glucose uptake and enrichment of anabolic pathways, which can fuel tumour growth. These findings provide considerable insight into the role of autophagy in cancer and have important implications for autophagy inhibition in cancer therapy. In this regard, we also show that treatment of mice with the autophagy inhibitor hydroxychloroquine, which is currently being used in several clinical trials, significantly accelerates tumour formation in mice containing oncogenic Kras but lacking p53.

doi: 10.1038/nature12865

構造生物学:膜内在型プロテアーゼRce1によるファルネシル化CAAXタンパク質の分解の仕組み

Mechanism of farnesylated CAAX protein processing by the intramembrane protease Rce1 p.301

CAAX proteins have essential roles in multiple signalling pathways, controlling processes such as proliferation, differentiation and carcinogenesis. The ∼120 mammalian CAAX proteins function at cellular membranes and include the Ras superfamily of small GTPases, nuclear lamins, the γ-subunit of heterotrimeric GTPases, and several protein kinases and phosphatases. The proper localization of CAAX proteins to cell membranes is orchestrated by a series of post-translational modifications of the carboxy-terminal CAAX motifs (where C is cysteine, A is an aliphatic amino acid and X is any amino acid). These reactions involve prenylation of the cysteine residue, cleavage at the AAX tripeptide and methylation of the carboxyl-prenylated cysteine residue. The major CAAX protease activity is mediated by Rce1 (Ras and a-factor converting enzyme 1), an intramembrane protease (IMP) of the endoplasmic reticulum. Information on the architecture and proteolytic mechanism of Rce1 has been lacking. Here we report the crystal structure of a Methanococcus maripaludis homologue of Rce1, whose endopeptidase specificity for farnesylated peptides mimics that of eukaryotic Rce1. Its structure, comprising eight transmembrane α-helices, and catalytic site are distinct from those of other IMPs. The catalytic residues are located ∼10 Å into the membrane and are exposed to the cytoplasm and membrane through a conical cavity that accommodates the prenylated CAAX substrate. We propose that the farnesyl lipid binds to a site at the opening of two transmembrane α-helices, which results in the scissile bond being positioned adjacent to a glutamate-activated nucleophilic water molecule. This study suggests that Rce1 is the founding member of a novel IMP family, the glutamate IMPs.

doi: 10.1038/nature12754

遺伝学:クロマチン結合マップから明らかになるプロモーター–エンハンサーの長距離にわたる動的相互作用

Chromatin connectivity maps reveal dynamic promoter–enhancer long-range associations p.306

In multicellular organisms, transcription regulation is one of the central mechanisms modelling lineage differentiation and cell-fate determination. Transcription requires dynamic chromatin configurations between promoters and their corresponding distal regulatory elements. It is believed that their communication occurs within large discrete foci of aggregated RNA polymerases termed transcription factories in three-dimensional nuclear space. However, the dynamic nature of chromatin connectivity has not been characterized at the genome-wide level. Here, through a chromatin interaction analysis with paired-end tagging approach using an antibody that primarily recognizes the pre-initiation complexes of RNA polymerase II, we explore the transcriptional interactomes of three mouse cells of progressive lineage commitment, including pluripotent embryonic stem cells, neural stem cells and neurosphere stem/progenitor cells. Our global chromatin connectivity maps reveal approximately 40,000 long-range interactions, suggest precise enhancer–promoter associations and delineate cell-type-specific chromatin structures. Analysis of the complex regulatory repertoire shows that there are extensive colocalizations among promoters and distal-acting enhancers. Most of the enhancers associate with promoters located beyond their nearest active genes, indicating that the linear juxtaposition is not the only guiding principle driving enhancer target selection. Although promoter–enhancer interactions exhibit high cell-type specificity, promoters involved in interactions are found to be generally common and mostly active among different cells. Chromatin connectivity networks reveal that the pivotal genes of reprogramming functions are transcribed within physical proximity to each other in embryonic stem cells, linking chromatin architecture to coordinated gene expression. Our study sets the stage for the full-scale dissection of spatial and temporal genome structures and their roles in orchestrating development.

doi: 10.1038/nature12716

細胞生物学:一次繊毛は特殊化されたカルシウムシグナル伝達細胞小器官である

Primary cilia are specialized calcium signalling organelles p.311

Primary cilia are solitary, non-motile extensions of the centriole found on nearly all nucleated eukaryotic cells between cell divisions. Only ∼200–300 nm in diameter and a few micrometres long, they are separated from the cytoplasm by the ciliary neck and basal body. Often called sensory cilia, they are thought to receive chemical and mechanical stimuli and initiate specific cellular signal transduction pathways. When activated by a ligand, hedgehog pathway proteins, such as GLI2 and smoothened (SMO), translocate from the cell into the cilium. Mutations in primary ciliary proteins are associated with severe developmental defects. The ionic conditions, permeability of the primary cilia membrane, and effectiveness of the diffusion barriers between the cilia and cell body are unknown. Here we show that cilia are a unique calcium compartment regulated by a heteromeric TRP channel, PKD1L1–PKD2L1, in mice and humans. In contrast to the hypothesis that polycystin (PKD) channels initiate changes in ciliary calcium that are conducted into the cytoplasm, we show that changes in ciliary calcium concentration occur without substantially altering global cytoplasmic calcium. PKD1L1–PKD2L1 acts as a ciliary calcium channel controlling ciliary calcium concentration and thereby modifying SMO-activated GLI2 translocation and GLI1 expression.

doi: 10.1038/nature12833

細胞生物学:一次繊毛のカルシウムチャネルの直接記録と分子の同定

Direct recording and molecular identification of the calcium channel of primary cilia p.315

A primary cilium is a solitary, slender, non-motile protuberance of structured microtubules (9+0) enclosed by plasma membrane. Housing components of the cell division apparatus between cell divisions, primary cilia also serve as specialized compartments for calcium signalling and hedgehog signalling pathways. Specialized sensory cilia such as retinal photoreceptors and olfactory cilia use diverse ion channels. An ion current has been measured from primary cilia of kidney cells, but the responsible genes have not been identified. The polycystin proteins (PC and PKD), identified in linkage studies of polycystic kidney disease, are candidate channels divided into two structural classes: 11-transmembrane proteins (PKD1, PKD1L1 and PKD1L2) remarkable for a large extracellular amino terminus of putative cell adhesion domains and a G-protein-coupled receptor proteolytic site, and the 6-transmembrane channel proteins (PKD2, PKD2L1 and PKD2L2; TRPPs). Evidence indicates that the PKD1 proteins associate with the PKD2 proteins via coiled-coil domains. Here we use a transgenic mouse in which only cilia express a fluorophore and use it to record directly from primary cilia, and demonstrate that PKD1L1 and PKD2L1 form ion channels at high densities in several cell types. In conjunction with an accompanying manuscript, we show that the PKD1L1–PKD2L1 heteromeric channel establishes the cilia as a unique calcium compartment within cells that modulates established hedgehog pathways.

doi: 10.1038/nature12832

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