Morphology and function of membrane-bound organelles

Heald, Rebecca; Cohen-Fix, Orna

doi:10.1016/j.ceb.2013.10.006

Cited by 67 publications

(55 citation statements)

References 46 publications

(32 reference statements)

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“…Living cells are divided into functional compartments called organelles. In eukaryotes, lipid membranes create a diffusion barrier between organelles and the cytoplasm, such that each compartment maintains a distinct biochemical composition that is tailored to its function (1).…”

Section: Introductionmentioning

confidence: 99%

Clusters of bacterial RNA polymerase are biomolecular condensates that assemble through liquid-liquid phase separation

Ladouceur

Parmar

Biedzinski

et al. 2020

Preprint

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Once described as mere "bags of enzymes", bacterial cells are in fact highly organized, with many macromolecules exhibiting non-uniform localization patterns. Yet the physical and biochemical mechanisms that govern this spatial heterogeneity remain largely unknown. Here, we identify liquid-liquid phase separation (LLPS) as a mechanism for organizing clusters of RNA polymerase (RNAP) in E. coli. Using fluorescence imaging, we show that RNAP quickly transitions from a dispersed to clustered localization pattern as cells enter log phase in nutrientrich media. RNAP clusters are sensitive to hexanediol, a chemical that dissolves liquid-like compartments in eukaryotic cells. In addition, we find that the transcription antitermination factor NusA forms droplets in vitro and in vivo, suggesting that it may nucleate RNAP clusters. Finally, we use single-molecule tracking to characterize the dynamics of cluster components.Our results indicate that RNAP and NusA molecules move inside clusters, with mobilities faster than a DNA locus but slower than bulk diffusion through the nucleoid. We conclude that RNAP clusters are biomolecular condensates that assemble through LLPS. This work provides direct evidence for LLPS in bacteria and suggests that this process serves as a universal mechanism for intracellular organization across the tree of life. SignificanceBacterial cells are small and were long thought to have little to no internal structure. However, advances in microscopy have revealed that bacteria do indeed contain subcellular compartments. But how these compartments form has remained a mystery. Recent progress in larger, more complex eukaryotic cells has identified a novel mechanism for intracellular organization known as liquid-liquid phase separation. This process causes certain types of molecules to concentrate within distinct compartments inside the cell. Here, we demonstrate that the same process also occurs in bacteria. This work, together with a growing body of literature, suggests that liquidliquid phase separation is a universal mechanism for intracellular organization that extends across the tree of life.

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Section: Introductionmentioning

confidence: 99%

Clusters of bacterial RNA polymerase are biomolecular condensates that assemble through liquid-liquid phase separation

Ladouceur

Parmar

Biedzinski

et al. 2020

Preprint

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“…Fundamental questions in cell biology concern the regulation of both cell size and sizes of intracellular organelles. The fact that size is regulated within specific ranges suggests that size is important for function (Heald and Cohen-Fix, 2014;Heald and Gibeaux, 2018;Levy and Heald, 2012;Marshall, 2015Marshall, , 2016. Nuclear size control is of particular interest.…”

Section: Introductionmentioning

confidence: 99%

Cytoplasmic volume and limiting nucleoplasmin scale nuclear size duringXenopus laevisdevelopment

Chen

Tomschik

Nelson

et al. 2019

Preprint

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How nuclear size is regulated relative to cell size is a fundamental cell biological question. Reductions in both cell and nuclear sizes during Xenopus laevis embryogenesis provide a robust scaling system to study mechanisms of nuclear size regulation. To test if the volume of embryonic cytoplasm is limiting for nuclear growth, we encapsulated gastrula stage embryonic cytoplasm and nuclei in droplets of defined volume using microfluidics. Nuclei grew and reached new steady-state sizes as a function of cytoplasmic volume, supporting a limiting component mechanism of nuclear size control. Through biochemical fractionation, we identified the histone chaperone nucleoplasmin (Npm2) as a putative nuclear size-scaling factor. Cellular amounts of Npm2 decrease over development, and nuclear size was sensitive to Npm2 levels both in vitro and in vivo, affecting nuclear histone levels and chromatin organization. Thus, reductions in cell volume with concomitant decreases in Npm2 amounts represent a developmental mechanism of nuclear size-scaling that may also be relevant to cancers with increased nuclear size.

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“…One way in which this can be achieved are shape changes, because all deviations from a spherical shape will decrease the volume-to-surface ratio. Non-spherical shapes of membranes can be dictated by proteins or by changes in lipid distribution (Derganc et al, 2013;Frolov et al, 2011;Heald and Cohen-Fix, 2014;Rafelski and Marshall, 2008). Manipulation of the balance of membrane influx and efflux pathways can also increase or decrease the volume of the organellar envelope.…”

Section: Introductionmentioning

confidence: 99%

“…It appears to retain a well-inflated appearance, which suggests that the volume-to-surface ratio of the organelle envelope might be controlled. This can help to maintain the membrane tension and the concentration of lumenal macromolecules that are crucial for organelle function (Ellis, 2001;García-Pérez et al, 1999;Heald and Cohen-Fix, 2014;Upadhyaya and Sheetz, 2004).…”

Section: Introductionmentioning

confidence: 99%

Organelle size control – increasing vacuole content activates SNAREs to augment organelle volume through homotypic fusion

Desfougères

Neumann²,

Mayer

2016

Journal of Cell Science

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Cells control the size of their compartments relative to cell volume, but there is also size control within each organelle. Yeast vacuoles neither burst nor do they collapse into a ruffled morphology, indicating that the volume of the organellar envelope is adjusted to the amount of content. It is poorly understood how this adjustment is achieved. We show that the accumulating content of yeast vacuoles activates fusion of other vacuoles, thus increasing the volume-to-surface ratio. Synthesis of the dominant compound stored inside vacuoles, polyphosphate, stimulates binding of the chaperone Sec18/NSF to vacuolar SNAREs, which activates them and triggers fusion. SNAREs can only be activated by lumenal, not cytosolic, polyphosphate ( polyP). Control of lumenal polyP over SNARE activation in the cytosol requires the cytosolic cyclin-dependent kinase Pho80-Pho85 and the R-SNARE Nyv1. These results suggest that cells can adapt the volume of vacuoles to their content through feedback from the vacuole lumen to the SNAREs on the cytosolic surface of the organelle.

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Morphology and function of membrane-bound organelles

Cited by 67 publications

References 46 publications

Clusters of bacterial RNA polymerase are biomolecular condensates that assemble through liquid-liquid phase separation

Clusters of bacterial RNA polymerase are biomolecular condensates that assemble through liquid-liquid phase separation

Cytoplasmic volume and limiting nucleoplasmin scale nuclear size duringXenopus laevisdevelopment

Organelle size control – increasing vacuole content activates SNAREs to augment organelle volume through homotypic fusion

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