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Coupling delay controls synchronized oscillation in the segmentation clock 期刊论文
NATURE, 2020
作者:  Yoshioka-Kobayashi, Kumiko;  Matsumiya, Marina;  Niino, Yusuke;  Isomura, Akihiro;  Kori, Hiroshi;  Miyawaki, Atsushi;  Kageyama, Ryoichiro
收藏  |  浏览/下载：7/0  |  提交时间：2020/07/03

Individual cellular activities fluctuate but are constantly coordinated at the population level via cell-cell coupling. A notable example is the somite segmentation clock, in which the expression of clock genes (such as Hes7) oscillates in synchrony between the cells that comprise the presomitic mesoderm (PSM)(1,2). This synchronization depends on the Notch signalling pathway  inhibiting this pathway desynchronizes oscillations, leading to somite fusion(3-7). However, how Notch signalling regulates the synchronicity of HES7 oscillations is unknown. Here we establish a live-imaging system using a new fluorescent reporter (Achilles), which we fuse with HES7 to monitor synchronous oscillations in HES7 expression in the mouse PSM at a single-cell resolution. Wild-type cells can rapidly correct for phase fluctuations in HES7 oscillations, whereas the absence of the Notch modulator gene lunatic fringe (Lfng) leads to a loss of synchrony between PSM cells. Furthermore, HES7 oscillations are severely dampened in individual cells of Lfng-null PSM. However, when Lfng-null PSM cells were completely dissociated, the amplitude and periodicity of HES7 oscillations were almost normal, which suggests that LFNG is involved mostly in cell-cell coupling. Mixed cultures of control and Lfng-null PSM cells, and an optogenetic Notch signalling reporter assay, revealed that LFNG delays the signal-sending process of intercellular Notch signalling transmission. These results-together with mathematical modelling-raised the possibility that Lfng-null PSM cells shorten the coupling delay, thereby approaching a condition known as the oscillation or amplitude death of coupled oscillators(8). Indeed, a small compound that lengthens the coupling delay partially rescues the amplitude and synchrony of HES7 oscillations in Lfng-null PSM cells. Our study reveals a delay control mechanism of the oscillatory networks involved in somite segmentation, and indicates that intercellular coupling with the correct delay is essential for synchronized oscillation.


Monitoring cells of the mouse presomitic mesoderm using the Achilles reporter fused to HES7 sheds light on the mechanisms that underpin synchronous oscillations in the expression of clock genes between neighbouring cells.


  
Structural basis of DNA targeting by a transposon-encoded CRISPR-Cas system 期刊论文
NATURE, 2020, 577 (7789) : 271-+
作者:  Halpin-Healy, Tyler S.;  Klompe, Sanne E.;  Sternberg, Samuel H.;  Fernandez, Israel S.
收藏  |  浏览/下载：5/0  |  提交时间：2020/07/03

Bacteria use adaptive immune systems encoded by CRISPR and Cas genes to maintain genomic integrity when challenged by pathogens and mobile genetic elements(1-3). Type I CRISPR-Cas systems typically target foreign DNA for degradation via joint action of the ribonucleoprotein complex Cascade and the helicase-nuclease Cas3(4,5), but nuclease-deficient type I systems lacking Cas3 have been repurposed for RNA-guided transposition by bacterial Tn7-like transposons(6,7). How CRISPR- and transposon-associated machineries collaborate during DNA targeting and insertion remains unknown. Here we describe structures of a TniQ-Cascade complex encoded by the Vibrio cholerae Tn6677 transposon using cryo-electron microscopy, revealing the mechanistic basis of this functional coupling. The cryo-electron microscopy maps enabled de novo modelling and refinement of the transposition protein TniQ, which binds to the Cascade complex as a dimer in a head-to-tail configuration, at the interface formed by Cas6 and Cas7 near the 3'  end of the CRISPR RNA (crRNA). The natural Cas8-Cas5 fusion protein binds the 5'  crRNA handle and contacts the TniQ dimer via a flexible insertion domain. A target DNA-bound structure reveals critical interactions necessary for protospacer-adjacent motif recognition and R-loop formation. This work lays the foundation for a structural understanding of how DNA targeting by TniQ-Cascade leads to downstream recruitment of additional transposase proteins, and will guide protein engineering efforts to leverage this system for programmable DNA insertions in genome-engineering applications.


  
Population flow drives spatio-temporal distribution of COVID-19 in China 期刊论文
NATURE, 2020
作者:  Fernandez, Diego Carlos;  Komal, Ruchi;  Langel, Jennifer;  Ma, Jun;  Duy, Phan Q.;  Penzo, Mario A.;  Zhao, Haiqing;  Hattar, Samer
收藏  |  浏览/下载：69/0  |  提交时间：2020/07/03

Sudden, large-scale and diffuse human migration can amplify localized outbreaks of disease into widespread epidemics(1-4). Rapid and accurate tracking of aggregate population flows may therefore be epidemiologically informative. Here we use 11,478,484 counts of mobile phone data from individuals leaving or transiting through the prefecture of Wuhan between 1 January and 24 January 2020 as they moved to 296 prefectures throughout mainland China. First, we document the efficacy of quarantine in ceasing movement. Second, we show that the distribution of population outflow from Wuhan accurately predicts the relative frequency and geographical distribution of infections with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) until 19 February 2020, across mainland China. Third, we develop a spatio-temporal '  risk source'  model that leverages population flow data (which operationalize the risk that emanates from epidemic epicentres) not only to forecast the distribution of confirmed cases, but also to identify regions that have a high risk of transmission at an early stage. Fourth, we use this risk source model to statistically derive the geographical spread of COVID-19 and the growth pattern based on the population outflow from Wuhan  the model yields a benchmark trend and an index for assessing the risk of community transmission of COVID-19 over time for different locations. This approach can be used by policy-makers in any nation with available data to make rapid and accurate risk assessments and to plan the allocation of limited resources ahead of ongoing outbreaks.


Modelling of population flows in China enables the forecasting of the distribution of confirmed cases of COVID-19 and the identification of areas at high risk of SARS-CoV-2 transmission at an early stage.


  
Hair-bearing human skin generated entirely from pluripotent stem cells 期刊论文
NATURE, 2020
作者:  von Appen, Alexander;  LaJoie, Dollie;  Johnson, Isabel E.;  Trnka, Michael J.;  Pick, Sarah M.;  Burlingame, Alma L.;  Ullman, Katharine S.;  Frost, Adam
收藏  |  浏览/下载：52/0  |  提交时间：2020/07/03

Skin organoids generated in vitro from human pluripotent stem cells form complex, multilayered skin tissue with hair follicles, sebaceous glands and neural circuitry, and integrate with endogenous skin when grafted onto immunocompromised mice.


The skin is a multilayered organ, equipped with appendages (that is, follicles and glands), that is critical for regulating body temperature and the retention of bodily fluids, guarding against external stresses and mediating the sensation of touch and pain(1,2). Reconstructing appendage-bearing skin in cultures and in bioengineered grafts is a biomedical challenge that has yet to be met(3-9). Here we report an organoid culture system that generates complex skin from human pluripotent stem cells. We use stepwise modulation of the transforming growth factor beta (TGF beta) and fibroblast growth factor (FGF) signalling pathways to co-induce cranial epithelial cells and neural crest cells within a spherical cell aggregate. During an incubation period of 4-5 months, we observe the emergence of a cyst-like skin organoid composed of stratified epidermis, fat-rich dermis and pigmented hair follicles that are equipped with sebaceous glands. A network of sensory neurons and Schwann cells form nerve-like bundles that target Merkel cells in organoid hair follicles, mimicking the neural circuitry associated with human touch. Single-cell RNA sequencing and direct comparison to fetal specimens suggest that the skin organoids are equivalent to the facial skin of human fetuses in the second trimester of development. Moreover, we show that skin organoids form planar hair-bearing skin when grafted onto nude mice. Together, our results demonstrate that nearly complete skin can self-assemble in vitro and be used to reconstitute skin in vivo. We anticipate that our skin organoids will provide a foundation for future studies of human skin development, disease modelling and reconstructive surgery.


  
Very regular high-frequency pulsation modes in young intermediate-mass stars 期刊论文
NATURE, 2020, 581 (7807) : 147-+
作者:  Zhao, Chuangqi;  Zhang, Pengchao;  Zhou, Jiajia;  Qi, Shuanhu;  Yamauchi, Yoshihiro;  Shi, Ruirui;  Fang, Ruochen;  Ishida, Yasuhiro;  Wang, Shutao;  Tomsia, Antoni P.;  Jiang, Lei;  Liu, Mingjie
收藏  |  浏览/下载：10/0  |  提交时间：2020/07/03

Asteroseismology probes the internal structures of stars by using their natural pulsation frequencies(1). It relies on identifying sequences of pulsation modes that can be compared with theoretical models, which has been done successfully for many classes of pulsators, including low-mass solar-type stars(2), red giants(3), high-mass stars(4) and white dwarfs(5). However, a large group of pulsating stars of intermediate mass-the so-called delta Scuti stars-have rich pulsation spectra for which systematic mode identification has not hitherto been possible(6,7). This arises because only a seemingly random subset of possible modes are excited and because rapid rotation tends to spoil regular patterns(8-10). Here we report the detection of remarkably regular sequences of high-frequency pulsation modes in 60 intermediate-mass main-sequence stars, which enables definitive mode identification. The space motions of some of these stars indicate that they are members of known associations of young stars, as confirmed by modelling of their pulsation spectra.


The pulsation spectra of intermediate-mass stars (so-called delta Scuti stars) have been challenging to analyse, but new observations of 60 such stars reveal remarkably regular sequences of high-frequency pulsation modes.


  
Extant timetrees are consistent with a myriad of diversification histories 期刊论文
NATURE, 2020, 580 (7804) : 502-+
作者:  Bhaskar, M. K.;  Riedinger, R.;  Machielse, B.;  Levonian, D. S.;  Nguyen, C. T.;  Knall, E. N.;  Park, H.;  Englund, D.;  Loncar, M.;  Sukachev, D. D.;  Lukin, M. D.
收藏  |  浏览/下载：19/0  |  提交时间：2020/07/03

An infinite number of alternative diversification scenarios-which may have markedly different, but equally plausible, dynamics-can underpin a given time-calibrated phylogeny of extant species, suggesting many previous studies have over-interpreted phylogenetic evidence.


Time-calibrated phylogenies of extant species (referred to here as '  extant timetrees'  ) are widely used for estimating diversification dynamics(1). However, there has been considerable debate surrounding the reliability of these inferences(2-5) and, to date, this critical question remains unresolved. Here we clarify the precise information that can be extracted from extant timetrees under the generalized birth-death model, which underlies most existing methods of estimation. We prove that, for any diversification scenario, there exists an infinite number of alternative diversification scenarios that are equally likely to have generated any given extant timetree. These '  congruent'  scenarios cannot possibly be distinguished using extant timetrees alone, even in the presence of infinite data. Importantly, congruent diversification scenarios can exhibit markedly different and yet similarly plausible dynamics, which suggests that many previous studies may have over-interpreted phylogenetic evidence. We introduce identifiable and easily interpretable variables that contain all available information about past diversification dynamics, and demonstrate that these can be estimated from extant timetrees. We suggest that measuring and modelling these identifiable variables offers a more robust way to study historical diversification dynamics. Our findings also make it clear that palaeontological data will continue to be crucial for answering some macroevolutionary questions.


  
Recurrent interactions in local cortical circuits 期刊论文
NATURE, 2020, 579 (7798) : 256-+
作者:  Liu, Yang;  Nguyen, Phong T.;  Wang, Xun;  Zhao, Yuting;  Meacham, Corbin E.;  Zou, Zhongju;  Bordieanu, Bogdan;  Johanns, Manuel;  Vertommen, Didier;  Wijshake, Tobias;  May, Herman;  Xiao, Guanghua;  Shoji-Kawata, Sanae;  Rider, Mark H.
收藏  |  浏览/下载：8/0  |  提交时间：2020/07/03

Most cortical synapses are local and excitatory. Local recurrent circuits could implement amplification, allowing pattern completion and other computations(1-4). Cortical circuits contain subnetworks that consist of neurons with similar receptive fields and increased connectivity relative to the network average(5,6). Cortical neurons that encode different types of information are spatially intermingled and distributed over large brain volumes(5-7), and this complexity has hindered attempts to probe the function of these subnetworks by perturbing them individually(8). Here we use computational modelling, optical recordings and manipulations to probe the function of recurrent coupling in layer 2/3 of the mouse vibrissal somatosensory cortex during active tactile discrimination. A neural circuit model of layer 2/3 revealed that recurrent excitation enhances sensory signals by amplification, but only for subnetworks with increased connectivity. Model networks with high amplification were sensitive to damage: loss of a few members of the subnetwork degraded stimulus encoding. We tested this prediction by mapping neuronal selectivity(7) and photoablating(9,10) neurons with specific selectivity. Ablation of a small proportion of layer 2/3 neurons (10-20, less than 5% of the total) representing touch markedly reduced responses in the spared touch representation, but not in other representations. Ablations most strongly affected neurons with stimulus responses that were similar to those of the ablated population, which is also consistent with network models. Recurrence among cortical neurons with similar selectivity therefore drives input-specific amplification during behaviour.


Computational modelling, imaging and single-cell ablation in layer 2/3 of the mouse vibrissal somatosensory cortex reveals that recurrent activity in cortical neurons can drive input-specific amplification during behaviour.


  
Li metal deposition and stripping in a solid-state battery via Coble creep 期刊论文
NATURE, 2020, 578 (7794) : 251-+
作者:  Helmrich, S.;  Arias, A.;  Lochead, G.;  Wintermantel, T. M.;  Buchhold, M.;  Diehl, S.;  Whitlock, S.
收藏  |  浏览/下载：56/0  |  提交时间：2020/07/03

Solid-state lithium metal batteries require accommodation of electrochemically generated mechanical stress inside the lithium: this stress can be(1,2) up to 1 gigapascal for an overpotential of 135 millivolts. Maintaining the mechanical and electrochemical stability of the solid structure despite physical contact with moving corrosive lithium metal is a demanding requirement. Using in situ transmission electron microscopy, we investigated the deposition and stripping of metallic lithium or sodium held within a large number of parallel hollow tubules made of a mixed ionic-electronic conductor (MIEC). Here we show that these alkali metals-as single crystals-can grow out of and retract inside the tubules via mainly diffusional Coble creep along the MIEC/metal phase boundary. Unlike solid electrolytes, many MIECs are electrochemically stable in contact with lithium (that is, there is a direct tie-line to metallic lithium on the equilibrium phase diagram), so this Coble creep mechanism can effectively relieve stress, maintain electronic and ionic contacts, eliminate solid-electrolyte interphase debris, and allow the reversible deposition/stripping of lithium across a distance of 10 micrometres for 100 cycles. A centimetre-wide full cell-consisting of approximately 10(10) MIEC cylinders/solid electrolyte/LiFePO4-shows a high capacity of about 164 milliampere hours per gram of LiFePO4, and almost no degradation for over 50 cycles, starting with a 1x excess of Li. Modelling shows that the design is insensitive to MIEC material choice with channels about 100 nanometres wide and 10-100 micrometres deep. The behaviour of lithium metal within the MIEC channels suggests that the chemical and mechanical stability issues with the metal-electrolyte interface in solid-state lithium metal batteries can be overcome using this architecture.


By containing lithium metal within oriented tubes of a mixed ionic-electronic conductor, a 3D anode for lithium metal batteries is produced that overcomes chemomechanical stability issues at the electrolyte interface.


  
Antagonistic cooperativity between crystal growth modifiers 期刊论文
NATURE, 2020, 577 (7791) : 497-+
作者:  Ma, Wenchuan;  Lutsko, James F.;  Rimer, Jeffrey D.;  Vekilov, Peter G.
收藏  |  浏览/下载：9/0  |  提交时间：2020/07/03

Inhibitor pairs that suppress the crystallization of haematin, which is a part of malaria parasites'  physiology, show unexpected antagonism due to attenuation of step pinning by kink blockers.


Ubiquitous processes in nature and the industry exploit crystallization from multicomponent environments(1-5)  however, laboratory efforts have focused on the crystallization of pure solutes(6,7) and the effects of single growth modifiers(8,9). Here we examine the molecular mechanisms employed by pairs of inhibitors in blocking the crystallization of haematin, which is a model organic compound with relevance to the physiology of malaria parasites(10,11). We use a combination of scanning probe microscopy and molecular modelling to demonstrate that inhibitor pairs, whose constituents adopt distinct mechanisms of haematin growth inhibition, kink blocking and step pinning(12,13), exhibit both synergistic and antagonistic cooperativity depending on the inhibitor combination and applied concentrations. Synergism between two crystal growth modifiers is expected, but the antagonistic cooperativity of haematin inhibitors is not reflected in current crystal growth models. We demonstrate that kink blockers reduce the line tension of step edges, which facilitates both the nucleation of crystal layers and step propagation through the gates created by step pinners. The molecular viewpoint on cooperativity between crystallization modifiers provides guidance on the pairing of modifiers in the synthesis of crystalline materials. The proposed mechanisms indicate strategies to understand and control crystallization in both natural and engineered systems, which occurs in complex multicomponent media(1-3,8,9). In a broader context, our results highlight the complexity of crystal-modifier interactions mediated by the structure and dynamics of the crystal interface.


  
Improved protein structure prediction using potentials from deep learning 期刊论文
NATURE, 2020, 577 (7792) : 706-+
作者:  Ma, Runze;  Cao, Duanyun;  Zhu, Chongqin;  Tian, Ye;  Peng, Jinbo;  Guo, Jing;  Chen, Ji;  Li, Xin-Zheng;  Francisco, Joseph S.;  Zeng, Xiao Cheng;  Xu, Li-Mei;  Wang, En-Ge;  Jiang, Ying
收藏  |  浏览/下载：143/0  |  提交时间：2020/07/03

Protein structure prediction can be used to determine the three-dimensional shape of a protein from its amino acid sequence(1). This problem is of fundamental importance as the structure of a protein largely determines its function(2)  however, protein structures can be difficult to determine experimentally. Considerable progress has recently been made by leveraging genetic information. It is possible to infer which amino acid residues are in contact by analysing covariation in homologous sequences, which aids in the prediction of protein structures(3). Here we show that we can train a neural network to make accurate predictions of the distances between pairs of residues, which convey more information about the structure than contact predictions. Using this information, we construct a potential of mean force(4) that can accurately describe the shape of a protein. We find that the resulting potential can be optimized by a simple gradient descent algorithm to generate structures without complex sampling procedures. The resulting system, named AlphaFold, achieves high accuracy, even for sequences with fewer homologous sequences. In the recent Critical Assessment of Protein Structure Prediction(5) (CASP13)-a blind assessment of the state of the field-AlphaFold created high-accuracy structures (with template modelling (TM) scores(6) of 0.7 or higher) for 24 out of 43 free modelling domains, whereas the next best method, which used sampling and contact information, achieved such accuracy for only 14 out of 43 domains. AlphaFold represents a considerable advance in protein-structure prediction. We expect this increased accuracy to enable insights into the function and malfunction of proteins, especially in cases for which no structures for homologous proteins have been experimentally determined(7).