Abstract
The ability of proteins and nucleic acids to undergo liquid–liquid phase separation has recently emerged as an important molecular principle of how cells rapidly and reversibly compartmentalize their components into membrane-less organelles such as the nucleolus, processing bodies or stress granules1,2. How the assembly and turnover of these organelles are controlled, and how these biological condensates selectively recruit or release components are poorly understood. Here we show that members of the large and highly abundant family of RNA-dependent DEAD-box ATPases (DDXs)3 are regulators of RNA-containing phase-separated organelles in prokaryotes and eukaryotes. Using in vitro reconstitution and in vivo experiments, we demonstrate that DDXs promote phase separation in their ATP-bound form, whereas ATP hydrolysis induces compartment turnover and release of RNA. This mechanism of membrane-less organelle regulation reveals a principle of cellular organization that is conserved from bacteria to humans. Furthermore, we show that DDXs control RNA flux into and out of phase-separated organelles, and thus propose that a cellular network of dynamic, DDX-controlled compartments establishes biochemical reaction centres that provide cells with spatial and temporal control of various RNA-processing steps, which could regulate the composition and fate of ribonucleoprotein particles.
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Data availability
The datasets generated in this study are available from the corresponding author upon request.
Code availability
Diatrack is available at www.diatrack.org. Additional Matlab codes used in this study are available from www.diatrack.org/DiatrackMaria.zip.
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Acknowledgements
We would like to thank G. Stojanovski and M. Martinovic for technical assistance. We are grateful to A. Sachs and J. Liphardt for plasmids, S. Jonas, M. Jinek, P. Kimming, E. Dultz, S. Khawaja, C. Weber and M. Zedan for their critical reading of this manuscript, ScopeM and J. Kusch for help with microscopy, M. Linsenmeier and A. Küffner for discussions of image and protein sequence analysis, and members of the Weis laboratory for discussions and comments. M.H. was supported by a Human Frontier Science Program (HFSP) postdoctoral fellowship (LT000914/2015) and an ETH postdoctoral fellowship (FEL-37-14-2). S.H. and M.H. acknowledge support from an EMBO long-term fellowship (ALTF 290-2014, EMBOCOFUND2012, GA-2012-600394 to S.H.; ALTF 870-2014 to M.H.). This work was supported by the Swiss National Science Foundation (SNF 31003A_179275 and 31003A_159731 to K.W.).
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Contributions
M.H. and K.W. conceptualized and organized the project and wrote the manuscript. M.H. analysed protein sequences, designed and performed all in vitro experiments and the E. coli imaging. R.S. designed, performed and analysed yeast experiments in Figs. 1c and 4a. M.H., R.S. and S.H. designed, performed and analysed yeast experiments in Fig. 3a. S.H. designed, performed and analysed yeast experiments in Fig. 3f. J.W. and B.M.A.F. designed, performed and analysed experiments on human cell lines. P.V. and M.H. analysed images for the Dhh1 phase diagram and the bacterial protein expression. K.W. provided experimental input, contributed to fluorescence polarization experiments and supervised the study. All authors contributed to editing the manuscript.
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Extended data figures and tables
Extended Data Fig. 1 Phase separation behaviour of full-length and tail-less (core) Dhh1 in different pH conditions.
a, Example images for the Dhh1 pH phase diagram. Reactions were assembled in 384-well plates; reaction conditions are described in Supplementary Table 5. Reactions were incubated at room temperature for 20 min and imaged at room temperature on a Nikon wide-field microscope using an automated script (four images per well of one replicate). Dhh1 core denotes Dhh1 (residues 48–425), which lacks the low-complexity tails. Scale bars, 50 μm. b, c, For each well, individual droplets in each image were quantified using Diatrack (see Methods) for their area and mean intensity. The sum of the product of area × mean fluorescence intensity (arbitrary unit: A × I) of all droplets in one image was plotted against the Dhh1 concentration (μM). Data are mean (lines) and s.d. (shaded areas) of the four images recorded per well for one replicate. d, Mean values of the sum of (area × mean fluorescence intensity) of the four images recorded per well were plotted against Dhh1 concentration for all pH values tested. Dhh1 core protein concentrations not tested are marked by a cross.
Extended Data Fig. 2 Phase separation behaviour of full-length and tail-less (core) Dhh1 in different salt concentrations.
a, Example images for the Dhh1 salt phase diagram at pH 6.4 and 7.0. Reactions were assembled in 384 well plates; reaction conditions are described in Supplementary Table 5. Reactions were incubated at room temperature for 20 min and imaged at room temperature on a Nikon wide-field microscope using an automated script (nine images per well of one replicate). Scale bars, 50 μm. b, c, For each well, individual droplets in each image were quantified using Diatrack (see Methods) for their area and mean intensity. The sum of the product of area × mean fluorescence intensity (A × I) of all droplets in one image was plotted against the Dhh1 concentration. Data are mean (lines) and s.d. (shaded areas) of the nine images recorded per well for one replicate. d, Mean values of the (area × mean fluorescence intensity) sum of the nine images recorded per well are plotted against the Dhh1 concentration for all conditions tested. Dhh1 core protein concentrations not tested are marked by a cross.
Extended Data Fig. 3 Phase separation behaviour of full-length and tail-less (core) Dhh1 in different ATP concentrations.
a, Example images for the Dhh1 ATP phase diagram at pH 6.4 and 7.0. Reactions were assembled in 384-well plates; reaction conditions are described in Supplementary Table 5. Reactions were incubated at room temperature for 20 min and imaged at room temperature on a Nikon wide-field microscope using an automated script (nine images per well of one replicate). Scale bars, 50 μm. b–e, For each well, individual droplets in each image were quantified using Diatrack (see Methods) for their area and mean intensity. The sum of the product of area × mean fluorescence intensity (A × I) of all droplets in one image was plotted against the Dhh1 concentration. Data are mean (lines) and s.d. (shaded areas) of the nine images recorded per well for one replicate. pH 6.4 (b, d) and pH 7.0 (c, e). f, Mean values of the (area ×mean fluorescence intensity) sum of the nine images recorded per well are plotted against the Dhh1 concentration for all conditions tested. Dhh1 core protein concentrations not tested are marked by a cross.
Extended Data Fig. 4 Phase separation behaviour of full-length and tail-less (core) Dhh1 in different polyU concentrations.
a, Example images for the Dhh1 polyU phase diagram at pH 6.4 and 7.0. Reactions were assembled in 384-well plates; reaction conditions are described in Supplementary Table 5. Reactions were incubated at room temperature for 20 min and imaged at room temperature on a Nikon wide-field microscope using an automated script (nine images per well of one replicate). Scale bars, 50 μm. b, c, For each well, individual droplets in each image were quantified using Diatrack (see Methods) for their area and mean intensity. The sum of the product of area × mean fluorescence intensity (A × I) of all droplets in one image was plotted against the Dhh1 concentration. Data are mean (lines) and s.d. (shaded areas) of the nine images recorded per well for one replicate. d, Mean values of the (area × mean fluorescence intensity) sum of the nine images recorded per well are plotted against the Dhh1 concentration for all conditions tested. Dhh1 core protein concentrations not tested are marked by a cross.
Extended Data Fig. 5 Dhh1, Ded1 and orthologues have unstructured low-complexity sequences in their N- and C-terminal tails.
a, High-magnification images of the samples represented in Fig. 1c. Scale bars, 5 μm. Dcp2, the catalytic subunit of the Dcp1–Dcp2 mRNA decapping complex, is used as a marker of processing bodies. Images are representative of more than four independent experiments. b, Clustal Omega sequence alignment of yeast DDXs (Dhh1 and Ded1) and their human counterparts (DDX6X and DDX3X, respectively). The RecA core is displayed in green; asterisks indicate sequence identity, dots represent sequence similarity. c, Schematic representation of low-complexity sequence distribution in the unstructured tails of Arabidopsis thaliana DDXs. Clustal Omega sequence alignment of yeast Dhh1 with its three A. thaliana orthologues (AT4G00660, AT3G61240 and AT2G45810).
Extended Data Fig. 6 Three of the five E. coli DEAD-box ATPases contain low-complexity sequences, undergo phase separation in vitro and form foci in vivo.
a, Clustal Omega sequence alignment of the five E. coli DEAD-box ATPases. The RecA core is displayed in green; asterisks indicate sequence identity, dots represent sequence similarity. b, In vitro phase separation of E.coli SrmB–mCherry (6 µM) and DbpA–mCherry (6 µM) in the presence of ATP and RNA. Scale bars, 25 μm. Images are representative of three independent experiments. c, Individual imaging channels of the composite images presented in Fig. 2e. Images are representative of more than three independent experiments. Scale bars, 2 μM. d, High-magnification view of expression of E. coli DDX–mCherry samples. Scale bar, 15 µm. Images are representative of three independent experiments. e, Quantification of foci in E. coli samples for four images per construct. Cells were segmented and for each individual cell, the mean fluorescence intensity and number of foci was quantified. Cells with 0 or 1 foci were grouped for technical reasons (see Methods). Cells were binned based on the mean fluorescence intensity, which represents their expression level, and the three highest bins were excluded from further analysis because they contain cells in which fluorescence intensity has reached saturation. The percentage of cells containing 0/1, 2, 3 or more than 3 foci are plotted for each bin. There is no correlation between expression levels and focus formation in the various strains.
Extended Data Fig. 7 The catalytically deficient mutant Ded1DQAD forms constitutive stress granules, without being compromised for RNA or ATP binding.
a, Ded1DQAD–mCherry, but not wild-type Ded1–mCherry, forms stress granules (arrows) in unstressed cells. Images are representative of more than three independent experiments. Scale bars, 5 µm. b, Fluorescence polarization analysis to measure binding of MANT-ATP to either wild-type Ded1 or Ded1DQAD. c, Fluorescence polarization analysis to measure binding of a fluorescein-UTP-labelled, 100-bp-long RNA to either wild-type Ded1 or Ded1DQAD. In b and c, data are mean and s.d. from n = 3 technical replicates. Nonlinear fit (on site-binding curve) calculated using Prism (GraphPad).
Extended Data Fig. 8 The ATPase activity of Ded1 controls disassembly of stress granules.
High-magnification view of the experiment in Fig. 1b, including more time points and dimethylsulfoxide (DMSO)-treated control samples. Scale bars, 5 μm. Images are representative of three biological replicates.
Extended Data Fig. 9 DDX ATPase activity controls the turnover of nuclear compartments in human and yeast.
a, b, Depletion of the DDX ATPase UAP56 leads to an increase in nuclear speckle size. This is consistent with the model that UAP56, which does not contain LCDs and is not an essential ‘building block’ for nuclear speckles, is required for RNA turnover in speckles, and its absence would thus lead to an increased residence time of RNA in the compartment and a subsequent increase in the size of pre-existing compartments. a, A549 cells were transfected with control siRNA or UAP56 siRNA that targets the 3′ untranslated region. After 48 h, cells were infected with influenza virus (strain WSN) at a multiplicity of infection of 10 for 6 h. Cells were subjected to single-molecule RNA FISH to label viral M mRNA, and nuclear speckles were detected by immunostaining with an anti-SON antibody. ‘Viral M RNA’ is an influenza virus transcript that has been described to traffic through nuclear speckles22 and is used as a model to represent poly-adenylated, spliced cellular transcripts. Insets denote enlargements of the white squares. Scale bar, 10 μm. Images are representative of three independent experiments. b, The percentage of viral M mRNA at nuclear speckles was plotted against the nuclear speckle volume (423 nuclear speckles for each condition—control and UAP56 siRNA. c, Stably transfected A549 cells expressing wild-type or UAP56 mutant (E197A) were treated with UAP56 siRNA, and cells were subjected to immunostaining with an anti-SON antibody. Scale bars, 10 μm. Images are representative of three independent experiments. d, e, Selection and characterization of stably transfected A549 cells expressing wild-type or mutant (E197A) UAP56. For gel source data, see Supplementary Fig. 1. Images are representative of three independent experiments. d, Several cell clones stably expressing wild-type or mutant UAP56 were tested by western blot analysis using an anti-Flag antibody. Clone 2 of wild-type UAP56, and clone 3 of mutant UAP56 were selected for further studies. e, Immunofluorescence with an anti-Flag antibody shows similar expression levels of exogenous UAP56 or UAP56(E197A) in the selected stable cell lines. Scale bar, 10 μm. f, Merged images with nuclear envelope marker protein staining for experiments in Fig. 3f. Images are representative images of five (Sub2-degron) or six (Sub2) biological replicates. g, Cells were treated as in Fig. 4g. At time point t = 60 min after induction of reporter, induction cells were treated with either water or 5% 1.6 hexanediol for 20 min. Images are representative of three biological replicates. h, Quantification of the percentage of cells displaying either distinct nuclear RNA foci (transcription foci, TF; up to two to account for mitotic cells) or diffuse nuclear RNA signal in Sub2-depleted cells. Images are representative of five biological replicates with n > 380 cells per replicate. ***P = 0.0009, **** P < 0.0001, two-tailed unpaired t-test. Data are mean and s.e.m. Dots represent the mean of individual replicates.
Extended Data Fig. 10 DDX ATPase activity regulates transfer of RNA molecules between phase-separated compartments in vivo and in vitro.
a, b, In vivo, stress granule assembly after treatment with 0.5% sodium azide was monitored by Ded1–eGFP in cells expressing untagged wild-type Dhh1 or Dhh1DQAD as the sole copy, and in a dhh1Δ background. Quantification of stress granules per cell was performed using Diatrack. Images are representative of four biological replicates, with at least 855 (WT), 755 (dhh1Δ) or 106 (Dhh1DQAD) cells per replicate. Data are mean and s.d. ***P = 0.0003 (dhh1Δ), ***P = 0.0001 (Dhh1DQAD), two-tailed unpaired t-test. Dots represent mean of individual replicates. Scale bars, 5 µm. c, d, RNA transfer between Dhh1 and Ded1 droplets. c, Forward reaction: Dhh1–mCherry droplets were assembled with Cy5-labelled RNA and added to Ded1–GFP droplets. After the addition of Not1MIF4G, Dhh1 droplets dissolve and the Cy5-RNA accumulates in the Ded1 droplets. d, Inverse reaction: Ded1–mCherry droplets were assembled with Cy5-labelled RNA and added to Dhh1–GFP droplets. After addition of recombinant eIF4GC-terminus, Ded1 droplets dissolve, but the Cy5-RNA does not accumulate in the Dhh1 droplets. In contrast to the reaction shown in Fig. 4, no stabilizing agents (such as BSA or PEG) were added in c and d to make the results in the forward and inverse reaction comparable. The fluorescence intensity scaling was adjusted for the first image (before Not1 or eIF4G addition) to account for the sample dilution after the addition of Not1 or eIF4G. However, scaling of the Cy5 channel in the first image, and in the subsequent frames (20–180 s), is identical for the forward and inverse reactions to enable a direct visual comparison. e, Quantification of the reactions presented in c and d. For each experiment, the mean Cy5-RNA intensity accumulating in six Dhh1–GFP droplets is plotted over time after the addition of Not1 or eIF4G. For background correction, six identically sized areas outside of Dhh1–GFP droplets were quantified and subtracted from the intensity measured inside the Dhh1–GFP droplets. These experiments were repeated at least three times, with comparable results. Data are mean (line) and s.d. (shaded area) of six large droplets per movie and forward and inverse reaction. At t = 180 s, 16.7 ± 2.7% of the Cy5-RNA is enriched in Ded1–GFP droplets that occupy 5–7% of the surface area (n = 3 movies). f, Line scan of the Cy5 channel (raw data), at time point t = 180 s through Ded1 droplets shown in c. In the ‘forward’ reaction, Ded1 droplets enrich Cy5-RNA 2–3-fold over background.
Supplementary information
Supplementary Information
This file contains Supplementary Tables 1-5 and the gel source data.
Supplementary Data
Sequence analysis of DDX proteins from human, yeast and E. coli.
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Hondele, M., Sachdev, R., Heinrich, S. et al. DEAD-box ATPases are global regulators of phase-separated organelles. Nature 573, 144–148 (2019). https://doi.org/10.1038/s41586-019-1502-y
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DOI: https://doi.org/10.1038/s41586-019-1502-y
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