Current Biology Magazine has not yet been applied to all Primer cytoplasm and the distribution of breeding programs, and there are these macromolecules is subject to still some major crop species (e.g., Phase separation constant change. Early concepts to soybean, tomato, sunfl ower) that are explain these density fl uctuations recalcitrant to the currently available in biology proposed a role for local synthesis, procedures, or for which present anchoring or active transport. Yet these protocols are not effi cient enough. Simon Alberti concepts are insuffi cient to explain The understanding of the maize in the complex organization of cells. situ system should help to extend Cells have to organize their complex We now realize that cells can only be the DH technology to more species biochemistry to regulate their properly understood if we also consider or breeding programs by either metabolism and respond to changes the collective properties of biological directly knocking out the functional in the environment. Traditionally, macromolecules. ortholog of the maize gene, or if intracellular organization has been Chemists have known for a long needed by transferring the cellular associated with compartments that time that macromolecules can have and molecular knowledge acquired are surrounded by lipid membranes. collective properties. The science of on maize. In addition to these However, in recent years, phase macromolecular collectives is called applications, the identifi cation of transitions have emerged as a novel colloidal chemistry. One example of a the NLD/MTL/ZmPLA1 gene offers form of cellular organization. Phase colloid is Jell-O, which is composed a unique opportunity to explore the transition is a physical process of colored water and gelatin, a large, many mysteries of double fertilization whereby a substance changes string-like protein. Gelatin dissolves in plants. from one physical state to another. well in hot water; however, when the Examples are provided by the freezing water is cooled, the gelatin molecules Where can I fi nd out more? of water into ice (liquid to solid) or the become insoluble and sticky and then Britt, A.B., and Kuppu, S. (2016). Cenh3: heating of water to generate water form a cross-linked network. The result an emerging player in haploid induction vapor (liquid to gas). of this process is a hydrogel. Technology. Front. Plant Sci. 7, 357. Dunwell, J.M. (2010). Haploids in fl owering plants: Liquid–liquid phase separation is The concept of viewing cells as origins and exploitation. Plant Biotechnol. J. a special form of a phase transition colloidal systems was fi rst proposed 8, 377–424. Dwivedi, S.L., Britt, A.B., Tripathi, L., Sharma, that is particularly relevant for living in the late 19th century by Edmund S., Upadhyaya, H.D., and Ortiz, R. (2015). organisms. Here, a homogenous Wilson. Wilson pointed out that cells Haploids: Constraints and opportunities in solution of molecules spontaneously appear as if they are densely packed plant breeding. Biotechnol. Adv. 33, 812–829. Forster, B.P., Heberle-Bors, E., Kasha, K.J., separates (‘demixes’) into two with macromolecular phases or liquid and Touraev, A. (2007). The resurgence of coexisting liquid phases, a dense phase ‘coacervates’. Alexander Oparin haploids in higher plants. Trends Plant Sci. 12, that is enriched for these molecules and later considered these coacervates 368–375. Gilles, L.M., Khaled, A., Laffaire, J.-B., a phase that is depleted (Figure 1). The an essential constituent of the Chaignon, S., Gendrot, G., Laplaige, J., interface of these dense droplets forms primordial soup. However, these initial Bergès, H., Beydon, G., Bayle, V., Barret, P., et al. (2017). Loss of pollen-specifi c a boundary that allows the selective concepts of cellular organization were phospholipase NOT LIKE DAD triggers passage of some molecules but not eclipsed by the enormous success of gynogenesis in maize. EMBO J. 36, 707–717. others. The presence of this interface reductionist molecular biology. Very Ishii, T., Karimi-Ashtiyani, R., and Houben, A. (2016). Haploidization via chromosome makes it possible that liquid droplets recently, however, we have seen a elimination: Means and mechanisms. Annu. can function as compartments. Once revival of colloidal biochemistry. Key Rev. Plant Biol. 67, 421–438. formed, liquid droplet compartments was the realization that cells contain Jackson, D. (2017). No sex please, we’re (in) breeding. EMBO J. 36, 703–704. can also adopt different physical states; compartments that lack membranes. Kelliher, T., Starr, D., Richbourg, L., Chintamanani, they can, for example, harden into gel- S., Delzer, B., Nuccio, M.L., Green, J., Chen, Z., McCuiston, J., Wang, W., et al. or glass-like states or they can turn into Membrane-less organelles (2017). MATRILINEAL, a sperm-specifi c solid crystals. Thus, phase separation Membrane-less organelles are micron- phospholipase, triggers maize haploid allows the formation of a wide range of sized cellular structures that consist of induction. Nature 542, 105–109. Liu, C., Li, X., Meng, D., Zhong, Y., Chen, C., compartments with different physical large collections of macromolecules, Dong, X., Xu, X., Chen, B., Li, W., Li, L., et al. properties. such as RNAs and proteins. Modern (2017). A 4-bp insertion at ZmPLA1 encoding a putative phospholipase A generates haploid In this Primer, I introduce the imaging approaches are revealing an induction in maize. Mol. Plant 10, 520–522. emerging topic of biological phase increasing number of these structures Ren, J., Wu, P., Trampe, B., Tian, X., transitions. I further discuss how cells (Figure 2). One prominent example is Lübberstedt, T., and Chen, S. (2017). Novel technologies in doubled haploid line use phase transitions to regulate provided by the centrosome, which development. Plant Biotechnol. J., http:// biological functions and activities in organizes the microtubule network of dx.doi.org/10.1111/pbi.1280. order to increase their fi tness and cells. Another example is provided by chances of survival. processing bodies or P bodies, which 1Laboratoire Reproduction et store and degrade RNA. Then there Dé veloppement des Plantes, Univ Lyon, The colloidal nature of cells is the example of the nucleolus, an ENS de Lyon, UCB Lyon 1, CNRS, INRA, The cellular interior is not a well- assembly line for ribosomes: it has a F-69342, Lyon, France; 2Limagrain, Limagrain Field Seeds, Research Centre, mixed collection of molecules. fi brillar center, where the ribosomal F-63360 Gerzat, France. Macromolecules are enriched or RNA is produced, and two additional *E-mail: [email protected] depleted in certain areas of the intranucleolar compartments, which

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In a key paper in 2012, Mike Phase separation Protein Rosen and colleagues provided conc. the fi rst experimental evidence that multivalency — the availability of many different binding sites on a molecule — is the crucial parameter that determines whether or not a protein will undergo phase separation. C Critical Many proteins, especially those functioning in signaling or gene expression, contain tandem arrays of modular domains. Each of these interaction modules binds a particular Time ligand, often with relatively weak affi nity. The number of these different modules determines the valency of Protein Phase separation the molecule. Importantly, multivalent conc. proteins have a critical threshold for phase separation that depends on the number of modules and available ligands. Increasing the number of the modules promotes the formation of increasingly larger complexes that CCritical PTMs, temperature, manifest macroscopically as phase- ionic strength separated droplets. Thus, although the C Critical composition of cellular bodies appears to be complex, their formation may be governed by very simple rules, such as Time protein valency and the availability of Current Biology ligands. Another feature that strongly affects Figure 1. Protein phase separation. the phase behavior of proteins is their

Top: A protein forms dense liquid droplets above the critical concentration (Ccritical) for phase separa- solubility. Many phase-separating tion. The liquid droplets are stable as long as the total concentration is above the critical threshold. proteins have poor solubility in water. The droplets form a compartment that allows the diffusion of molecules within the compartment and Burying such insoluble proteins in a promotes the dynamic exchange of molecules with the dilute surrounding phase. Once the total protein concentration drops below the critical concentration again, the compartments dissolve and the system growing phase-separating structure relapses back to a one-phase state where the molecules are evenly distributed. The insets above show is energetically more favorable than original data from a phase separation experiment with purifi ed GFP-tagged FUS (a prion-like RNA- exposing these proteins to water. As binding protein). Bottom: Post-translational modifi cations (PTMs) or changes in temperature or ionic a consequence, solubility changes strength can increase the affi nity of protein–protein interactions, thus lowering the critical threshold for and phase separation are often phase separation and allowing compartment formation at a much lower protein concentration. coupled. This is particularly relevant for multidomain proteins that are assemble ribosomes from molecular protein–nucleic acid interactions connected by fl exible linkers. These components. is emerging as the key organizing linker sequences often have poor These examples illustrate that, principle of cellular condensates. solubility and can undergo weak despite the absence of membranes, Using this physical framework, we can interactions among themselves that these organelles can be very large in now study the assembly, composition can further drive the phase separation size and have a complex, multilayered and properties of membrane-less process. Thus, linker regions between organization. Recently, the term organelles. Early concepts to explain modular domains can make a strong ‘biomolecular condensate’ has been the formation of membrane-less contribution to the driving force of proposed to refer to these different organelles invoked a role for strong, phase separation. structures. Biomolecular condensates stereospecifi c interactions, but more Besides multidomain proteins, are highly abundant in eukaryotic recent work has emphasized the intrinsically disordered proteins (IDPs) cells. But how can these condensates importance of very weak interactions. have been implicated in promoting concentrate so many molecules in the It appears that both weak and phase separation. Unlike globular absence of membranes? strong interactions can contribute to proteins, these proteins do not have condensate formation, but what is a fi xed conformation and they are Molecular features driving biological most important is that many of these often characterized by low sequence phase transitions interactions take place at the same time complexity. This means that these Liquid–liquid phase separation driven to allow the formation of a network of IDPs use only a small subset of by collective protein–protein and interactions. the 20 available amino acids. The

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exact sequence of IDPs is often not important, but what matters for phase separation are simple charge patterns and the overall sequence composition. Several different types of IDPs with low sequence complexity have been identifi ed. One type is known as prion- Cajal bodies like because proteins with similar amino acid compositions have also been shown to form heritable aggregates, or prions. These proteins are composed of mostly polar amino acids, such Stress granules PML bodies as serine, tyrosine, glutamine, Membrane-less asparagine, and glycine. This sequence organelles composition often reduces the solubility of these proteins in water and promotes multivalent interactions. A second class of low-complexity IDPs contains high numbers of positively and/or negatively charged residues arranged in characteristic charge patterns. Such charged IDPs undergo electrostatic P bodies Nucleoli interactions that are highly sensitive Current Biology to the pH and ionic strength of the solution. Figure 2. Membrane-less organelles in HeLa cells. Phase separation can occur with The cells shown express different GFP-tagged marker proteins from bacterial artifi cial chromosomes one, two or multiple proteins. Phase (BACs) that localize to different membrane-less organelles. The marker proteins used are: coilin (Cajal separation of a single protein is also bodies), DCP1A (P bodies), MKI67 (nucleoli), G3BP1 (stress granules), and PML (PML bodies). Stress granules were induced with 1 mM arsenate for 30 minutes. The nucleus was stained with DAPI and known as simple coacervation; phase the red signal is the result of co-staining with an anti-tubulin antibody. Images courtesy of Ina Poser separation that requires complex (MPI-CBG). formation by two or more proteins is known as complex coacervation. experiments have taught us that has been reported to occur during the One protein that drives compartment different proteins have different critical DNA damage response. DNA damage formation by complex coacervation concentrations at which they undergo breaks lead to the recruitment of PAR is the nephrin intracellular domain phase separation (Figure 1). This polymerase 1 and the subsequent (NICD). NICD is a disordered, negatively suggests that condensate formation local formation of elaborate PAR charged protein that co-assembles could be initiated by the protein with structures in proximity to the DNA with positively charged protein partners the lowest critical concentration; other lesion. Proteins such as the prion- to form liquid droplets. Another proteins with a higher threshold could like protein FUS can subsequently example of complex coacervation is be recruited into droplets formed by bind to PAR and this increases their the interaction of arginine/glycine-rich proteins with a lower critical threshold. local protein concentration above RNA-binding proteins with RNA. In this This further implies that regulation the critical concentration for phase case, polyvalent interactions between of the protein with the lowest critical separation, resulting in the formation the positively charged arginine residues concentration could be the rate-limiting of a compartment that promotes the and the negatively charged RNA step for condensate formation in the recruitment of important DNA repair drive the phase separation process. cellular environment. enzymes. Many PAR polymerases are Our increasing understanding of the Besides protein nucleators, there present in eukaryotic cells and, while molecular mechanisms of phase also is evidence that polyvalent we do not know their exact functions, separation now allows us to unravel the polymers promote nucleation, as it is conceivable that each one of them principles underlying the formation of has been described for RNA and a promotes the formation of specifi c cellular bodies. molecule that is chemically related to nuclear or cytoplasmic bodies. RNA, called PAR or polyADP-ribose. Cells have to regulate where and Principles of condensate formation RNAs have been shown to lower when phase separation occurs. In and growth the critical concentration for phase principle, there are four ways in which The formation of phase-separated separation of RNA-binding proteins. this can be achieved (Figure 1): cells compartments is often impeded by a A seeding role for RNAs has also can regulate the protein concentration, kinetic barrier that has to be overcome been suggested by a study showing the solubility, the affi nity or the by nucleation. How condensates are that transcription is required for the valency of a phase-separating protein. nucleated in the cellular environment assembly of the nucleolus. Regulation Changes in protein concentration is largely unknown. However, in vitro of phase separation by PAR molecules could be induced by bursts of

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Active state The size of phase-separated bodies often changes with time, and liquid bodies can grow in two different ways. One possibility is Ostwald ripening, which describes the physical phenomenon of diffusion-limited A A B + movement of molecules from small to large droplets. Another possibility is growth by coalescence, which is when two small droplets come into close proximity, touch and then fuse into a larger droplet. A prerequisite [B] [B] for coalescence is that the cellular bodies can move freely by Brownian motion, although this is not always possible; for example, many nuclear bodies seem to be anchored to DNA or RNA, which restricts their movement and thus the ability to grow by coalescence. However, there also t t is evidence for active coalescence in cells. Cytoplasmic stress granules Repressed state undergo fusion events that are dependent on microtubules and motor proteins. This suggests that in living cells there are important links between phase separation — a thermodynamic Release equilibrium process — and non- A + B C equilibrium phenomena, such as directed transport.

Regulating the material properties of condensates Phase separation leads to the formation of dense liquid droplets [C] [C] that often exhibit a very high protein concentration. As we know from protein crystallization studies, a high protein concentration can favor nucleation and the formation of a crystal. It is also possible that proteins in the dense liquid phase become kinetically arrested with the droplet t t adopting a glass- or gel-like state. Current Biology Recent in vitro studies indeed indicate that reconstituted liquid droplets are Figure 3. Activation or repression of biological activities by phase separation. metastable and convert into a more Top: Two proteins A react to form a product B. In the absence of phase separation, the concentra- solid-like state with time. In the case tion of A is low, thus leading to a low reaction rate. Phase separation allows enrichment of A in a of the prion-like RNA-binding protein liquid droplet compartment, thus increasing the local concentration of A and accelerating the reac- FUS, the liquid droplets fi rst harden into tion rate. Protein A could for example be tubulin monomers that are enriched in a droplet compart- gels and then form crystal-like, fi brillar ment to promote nucleation into microtubules (B). Bottom: A factor A is sequestered in a gel-like compartment in a repressed state. Release of A from the compartment allows A to react with B, aggregates. This maturation process resulting in the formation of the product C. The factor A could for example be mRNAs that are stored has been called molecular aging and in RNP granules. When the mRNA is released, it is bound by translation factors (B) to synthesize it seems to affect a large fraction of new protein (C). reconstituted liquid droplets formed by different proteins. This time-dependent transcription or the release of a protein In fact, there now is increasing change of the material properties is from a storage depot. The solubility, evidence for regulation of membrane- now known as the continuum model of valency or affi nity of a protein could less compartments through post- phase separation. be regulated through ligand binding translational modifi cations, such as Evidence for molecular aging of or post-translational modifi cations. phosphorylation and methylation. compartments in cells is scarce.

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This suggests that cells use energy Phase separation has also been can envision that such emergent to regulate the material properties of shown to organize and facilitate properties are frequently associated their compartments to keep them in a signaling. This has been reported for with condensates. Condensates could, dynamic, liquid-like state. Moreover, the T-cell receptor, which can organize for example, provide mechanical recent studies suggest that phase into membrane-associated phase- stability by forming gels, they could separation alone is insuffi cient to separated clusters. Reconstitution generate molecular sieves that fi lter explain the distribution of proteins experiments revealed that these out molecules, or they could bend in membrane-less organelles. clusters promote the recruitment of membranes to promote membrane For example, the assembly of the specifi c sets of signaling proteins. fusion events. The theoretical functional nucleolus is dependent on active, Importantly, the clusters were enriched repertoire of biomolecular condensates energy-consuming processes, such for kinases but excluded phosphatases. seems vast. as transcription. How condensate Thus, phase separation could be an formation is regulated by energy- effective way to amplify signals and Phase separation and stress consuming enzymes in living cells will perform simple forms of computation. adaptation be an important area of research in the Cellular bodies are particularly Phase separation is extremely sensitive future. abundant in the nucleus. The key to changes in physico-chemical Recent studies aided by high- biological processes that take place conditions, suggesting that phase resolution imaging approaches in the nucleus are transcription separation could play an important have provided evidence that phase- and splicing, suggesting that role in stress adaptation. Cells put a lot separated cellular bodies have a phase separation could be used to of effort and energy into maintaining very complex internal organization. regulate these processes. Indeed, stable internal conditions. They It appears that many proteins heterochromatin has recently been have transporters and pumps that within these bodies localize to their shown to be a phase-separated keep the osmotic conditions, salt own territories or phases. A recent compartment. The presence concentration and pH in a range that study focused on the nucleolus to of a compartment boundary in is favorable for rapid growth. However, unravel the molecular basis of this heterochromatin may be necessary to when challenged with stress, cells multiphase organization. The authors sterically exclude certain factors, such are no longer able to maintain these could show that the multilayered as RNA polymerases. Furthermore, stable conditions. This could lead to organization of the nucleolus is the a phase separation model has been sudden changes in physico-chemical result of differences in the biophysical postulated for transcriptional control. conditions, which could in principle be properties of the nucleolar phases, Super-enhancer formation by phase read out by phase separation. If this most importantly the droplet surface separation was proposed to explain phase separation process is coupled to tension. Thus, the multilayered the bursting behavior of genes and changes in protein function, it could be structure of many cellular bodies may the simultaneous activation of multiple used to mount an adaptive response. be explained by the immiscibility of genes. However, experimental evidence In agreement with this idea, their different phases. for this model is still lacking. fl uctuations in cytosolic pH promote Although there now is increasing widespread condensate formation The functional repertoire of phase evidence that droplet compartments during stress. Recent studies indeed transitions can promote biochemical reactions, it is suggest that these condensates It is now clear that phase separation also conceivable that phase separation have adaptive roles. For example, gel is a key principle for organizing the can repress biochemical reactions formation by the RNA-binding protein intracellular environment. But what are (Figure 3). One example is provided by Pab1 has been proposed to regulate the functions of these cellular bodies? ribonucleoprotein (RNP) granules. RNP the availability of certain stress- One function may be to concentrate granules often store mRNAs, which are protective RNAs. It seems very likely biomolecules in a confi ned space and then transported in a silenced state to that stress adaptation through protein thus promote biochemical reactions diverse locations. By doing so, RNP phase separation is a widespread (Figure 3). Cells seem to use this granules promote the distribution of phenomenon in nature. principle for regulating the formation of information in cells. In neurons, this The sensitivity of phase-separating cytoskeletal structures. For example, allows the local synthesis of proteins in proteins to changing physico-chemical reconstituted pericentriolar material synapses and in dendrites upon demand. conditions also comes with a cost can drive microtubule formation by Are there other functions associated because many phase-separating raising the concentration of tubulin with condensates? Because phase- proteins are associated with age- above the critical concentration for separated compartments are collectives related diseases. In fact, aberrant nucleation. The nucleation of actin of many interacting molecules, they can phase transitions may be a key driver fi laments also seems to be promoted in principle have emergent properties. of aging and disease, given that aging by phase separation. A multivalent As an analogy, many water molecules cells often lose control over their system of at least three interacting can assemble into a droplet, which internal conditions. Thus, the concept proteins drives the recruitment of displays the emergent property of of biological phase transitions may the actin nucleator Arp2/3, which wetness. Importantly, wetness is a also lead to new insights into diseases subsequently leads to the formation of collective property that is absent and create new opportunities for actin fi laments on membranes. from individual water molecules. One therapeutic interventions.

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Outlook Correspondence weaker dissociation levels [2]. The framework of biological phase Generally inspired by the comparator transitions has revolutionized our Distinct locomotor framework [3], such paradigms understanding of cells and organisms. quantify participants’ motor awareness But this emerging fi eld is still young. control and and performance when exposed to Questions that we need to address are: different spatiotemporal mismatches what is the molecular grammar of phase awareness in awake concerning auditory or visual feedback separation? How do cells regulate phase sleepwalkers about on-going movements [4,5]. Such separation? How do cells generate paradigms have recently been adapted compartments with different identities? to locomotion, and in combination To what extent are phase transitions Oliver A. Kannape1,2, with dual tasking [6] have illustrated able to explain the complexity of cells, Stephen Perrig3, Andrea O. Rossetti4, an increased dissociation between and how are phase transitions coupled and Olaf Blanke2,5,6,* locomotor control and awareness under to active processes? How do cells use cognitive load [7,8]. phase separation to adapt to different Sleepwalkers’ complex nocturnal To investigate both locomotor control environments, and how do different behaviors have inspired fi ctional and awareness in sleepwalkers, we environments shape the evolution of characters from Shakespeare’s Lady asked a group of clinically diagnosed phase-separating proteins? Can the Macbeth to Polidori’s Vampyre to sleepwalkers and a group of age- and concept of phase separation help Cesare, the homicidal somnambulist in gender-matched control participants to us understand and treat age-related The Cabinet of Dr Caligari. Yet although move their tracked, virtual body into a diseases such as neurodegeneration the underlying pathophysiology of virtual target cylinder by performing the and cancer? sleepwalking, i.e. the partial arousal corresponding goal-directed movement from slow-wave sleep, is today well- in the tracking arena (Figure 1A, FURTHER READING documented, the detailed sensorimotor see Experimental Procedures in mechanisms permitting locomotion Supplemental Information, published Alberti, S., and Hyman, A.A. (2016). Are aberrant and further complex behaviors to with this article online). Feedback of phase transitions a driver of cellular aging? Bioessays 38, 959–968. occur outside of conscious control walking trajectories could be veridical Banani, S.F., Lee, H.O., Hyman, A.A., and Rosen, remain poorly understood [1]. Further, or randomly deviated to the left/right M.K. (2017). Biomolecular condensates: organizers of cellular biochemistry. Nat. Rev. Mol. the paroxysmal character, nocturnal by 5°–30° such that participants had to Cell Biol. 18, 285–298. pattern, and spontaneous onset have compensate for the deviation in order Brangwynne, C.P., Eckmann, C.R., Courson, D.S., made it nigh on impossible to study to reach the target [8]. Participants Rybarska, A., Hoege, C., Gharakhani, J., Jülicher, F., and Hyman, A.A. (2009). Germline somnambulism behaviorally during rated the veracity of the received P granules are liquid droplets that localize by wakefulness. The goal-directed walking feedback after each trial (yes/no). controlled dissolution/condensation. Science 324, 1729–1732. paradigm reported here, based on full- The secondary task was articulated Feric, M., Vaidya, N., Harmon, T.S., Mitrea, D.M., Zhu, body motion capture and virtual reality backwards counting (steps of 7), a L., Richardson, T.M., Kriwacki, R.W., Pappu, R.V., feedback, directly addresses this issue task reliably shown to interfere with and Brangwynne, C.P. (2016). Coexisting liquid phases underlie nucleolar subcompartments. Cell and provides unique insights into the locomotor control (independent of 165, 1686–1697. functional mechanisms of this common errors in arithmetic) [6]. Hyman, A.A., Weber, C.A., and Jülicher, F. (2014). Liquid-liquid phase separation in biology. Annu. parasomnia: sleepwalkers exhibited All participants correctly performed Rev. Cell Dev. Biol. 30, 39–58. improved movement automation the task and accurately identifi ed Li, P., Banjade, S., Cheng, H.-C., Kim, S., Chen, B., and a stronger dissociation between that the virtual body refl ected their Guo, L., Llaguno, M., Hollingsworth, J.V., King, D.S., Banani, S.F., et al. (2012). Phase locomotor control and awareness than own movements in control trials transitions in the assembly of multivalent matched controls when challenged with (93 ± 2% µ ± SEM self-attribution, cf. signalling proteins. Nature 483, 336–340. Patel, A., Lee, H.O., Jawerth, L., Maharana, S., a cognitive load. Our data therefore Table S1) and correctly rejected strongly Jahnel, M., Hein, M.Y., Stoynov, S., Mahamid, J., suggest that behavioral markers exist deviated trials (4 ± 2% self-attribution for Saha, S., Franzmann, T.M., et al. (2015). A in awake sleepwalkers, characterized 30º mismatch, main effect of Deviation: liquid-to-solid phase transition of the ALS protein FUS accelerated by disease mutation. Cell 162, by their ability to perform complex P < 0.001), closely replicating previous 1066–1077. locomotor actions in the absence results [7,8] (Bayes factor analysis Rabouille, C., and Alberti, S. (2017). Cell adaptation upon stress: the emerging role of membrane-less of full consciousness. Our fi ndings BF = 4.58, half-normal prior derived from compartments. Curr. Opin. Cell Biol. 47, 34–42. are important as they fi rmly link [8]). As illustrated in Figure 1D, there Riback, J.A., Katanski, C.D., Kear-Scott, J.L., sleepwalking to the neuroscience of were no overt differences in locomotor Pilipenko, E.V., Rojek, A.E., Sosnick, T.R., and Drummond, D.A. (2017). Stress-triggered phase motor control and motor awareness awareness thresholds (controls: separation is an adaptive, evolutionarily tuned and may complement formal diagnosis 13.4° ± 1.5, sleepwalkers: 13.2° ± 1.7) or response. Cell 168, 1028–1040.e19. Su, X., Ditlev, J.A., Hui, E., Xing, W., Banjade, S., procedures (normally requiring time, walking performance (accuracy, velocity) Okrut, J., King, D.S., Taunton, J., Rosen, M.K., cost-intensive sleep studies and between the groups in the single task and Vale, R.D. (2016). Phase separation of polysomnographic recordings). condition. signaling molecules promotes T cell receptor signal transduction. Science 352, 595–599. Dissociations between automated However, under cognitive load, our motor control and awareness, so study reveals two key fi ndings that Max Planck Institute of Molecular Cell Biology striking in each sleepwalking episode, link sleepwalking to motor control and Genetics, 01307 Dresden, Germany. have been extensively studied in and motor awareness in wakefulness. E-mail: [email protected] healthy populations, albeit at much The fi rst important fi nding is the

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