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[
Nat Struct Mol Biol,
2019]
RNA granules are subcellular compartments that are proposed to form by liquid-liquid phase separation (LLPS), a thermodynamic process that partitions molecules between dilute liquid phases and condensed liquid phases. The mechanisms that localize liquid phases in cells, however, are not fully understood. P granules are RNA granules that form in the posterior of Caenorhabditis elegans embryos. Theoretical studies have suggested that spontaneous LLPS of the RNA-binding protein PGL-3 with RNA drives the assembly of P granules. We find that the PGL-3 phase is intrinsically labile and requires a second phase for stabilization in embryos. The second phase is formed by gel-like assemblies of the disordered protein MEG-3 that associate with liquid PGL-3 droplets in the embryo posterior. Co-assembly of gel phases and liquid phases confers local stability and long-range dynamics, both of which contribute to localized assembly of P granules. Our findings suggest that condensation of RNA granules can be regulated spatially by gel-like polymers that stimulate LLPS locally in the cytoplasm.
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[
Nat Struct Mol Biol,
2020]
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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[
International C. elegans Meeting,
1989]
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[
Development,
2023]
A hallmark of all germ cells is the presence of germ granules: assemblies of proteins and RNA that lack a delineating membrane and are proposed to form via condensation. Germ granules across organisms share several conserved components, including factors required for germ cell fate determination and maintenance, and are thought to be linked to germ cell development. The molecular functions of germ granules, however, remain incompletely understood. In this Development at a Glance article, we survey germ granules across organisms and developmental stages, and highlight emerging themes regarding granule regulation, dynamics and proposed functions.
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[
Elife,
2021]
Germ granules are protein-RNA condensates that segregate with the embryonic germline. In <i>C. elegans</i> embryos, germ (P) granule assembly requires MEG-3, an intrinsically-disordered protein that forms RNA-rich condensates on the surface of PGL condensates at the core of P granules. MEG-3 is related to the GCNA family and contains an N-terminal disordered region (IDR) and a predicted ordered C-terminus featuring an HMG-like motif (HMGL). We find that MEG-3 is modular protein that uses its IDR to bind RNA and its C-terminus to drive condensation. The HMGL motif mediates binding to PGL-3 and is required for co-assembly of MEG-3 and PGL-3 condensates <i>in vivo</i>. Mutations in HMGL cause MEG-3 and PGL-3 to form separate condensates that no longer co-segregate to the germline or recruit RNA. Our findings highlight the importance of protein-based condensation mechanisms and condensate-condensate interactions in the assembly of RNA-rich germ granules.
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[
Science,
2021]
Biomolecular condensates are cellular compartments that can form by phase separation in the absence of limiting membranes. Studying the P granules of Caenorhabditis elegans, we find that condensate dynamics are regulated by protein clusters that adsorb to the condensate interface. Using in vitro reconstitution, live observations, and theory, we demonstrate that localized assembly of P granules is controlled by MEG-3, an intrinsically disordered protein that forms low dynamic assemblies on P granules. Following classic Pickering emulsion theory, MEG-3 clusters lower surface tension and slow down coarsening. During zygote polarization, MEG-3 recruits the DYRK family kinase MBK-2 to accelerate spatially regulated growth of the P granule emulsion. By tuning condensate-cytoplasm exchange, interfacial clusters regulate the structural integrity of biomolecular condensates, reminiscent of the role of lipid bilayers in membrane-bound organelles.
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[
Elife,
2020]
RNA granules are protein/RNA condensates. How specific mRNAs are recruited to cytoplasmic RNA granules is not known. Here we characterize the transcriptome and assembly of P granules, RNA granules in the <i>C. elegans</i> germ plasm. We find that P granules recruit mRNAs by condensation with the disordered protein MEG-3. MEG-3 traps mRNAs into non-dynamic condensates <i>in vitro</i> and binds to ~500 mRNAs <i>in vivo</i> in a sequence-independent manner that favors embryonic mRNAs with low ribosome coverage. Translational stress causes additional mRNAs to localize to P granules and translational activation correlates with P granule exit for two mRNAs coding for germ cell fate regulators. Localization to P granules is not required for translational repression but is required to enrich mRNAs in the germ lineage for robust germline development. Our observations reveal similarities between P granules and stress granules and identify intrinsically-disordered proteins as drivers of RNA condensation during P granule assembly.
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Barnes JR, Heistad RM, Leary SC, Knudsen KJ, Pennington PR, Quartey MO, Buttigieg J, Maley JM, De Carvalho CE, Mousseau DD, Parsons MP, Nyarko JNK, Bolanos MAC
[
Sci Rep,
2021]
The pool of -Amyloid (A) length variants detected in preclinical and clinical Alzheimer disease (AD) samples suggests a diversity of roles for A peptides. We examined how a naturally occurring variant, e.g. A(1-38), interacts with the AD-related variant, A(1-42), and the predominant physiological variant, A(1-40). Atomic force microscopy, Thioflavin T fluorescence, circular dichroism, dynamic light scattering, and surface plasmon resonance reveal that A(1-38) interacts differently with A(1-40) and A(1-42) and, in general, A(1-38) interferes with the conversion of A(1-42) to a -sheet-rich aggregate. Functionally, A(1-38) reverses the negative impact of A(1-42) on long-term potentiation in acute hippocampal slices and on membrane conductance in primary neurons, and mitigates an A(1-42) phenotype in Caenorhabditis elegans. A(1-38) also reverses any loss of MTT conversion induced by A(1-40) and A(1-42) in HT-22 hippocampal neurons and APOE 4-positive human fibroblasts, although the combination of A(1-38) and A(1-42) inhibits MTT conversion in APOE 4-negative fibroblasts. A greater ratio of soluble A(1-42)/A(1-38) [and A(1-42)/A(1-40)] in autopsied brain extracts correlates with an earlier age-at-death in males (but not females) with a diagnosis of AD. These results suggest that A(1-38) is capable of physically counteracting, potentially in a sex-dependent manner, the neuropathological effects of the AD-relevant A(1-42).
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[
Worm Breeder's Gazette,
2003]
Wormgenes is a new resource for C.elegans offering a detailed summary about each gene and a powerful query system.
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[
Front Pharmacol,
2020]
Oligomeric assembly of Amyloid- (A) is the main toxic species that contribute to early cognitive impairment in Alzheimer's patients. Therefore, drugs that reduce the formation of A oligomers could halt the disease progression. In this study, by using transgenic <i>Caenorhabditis elegans</i> model of Alzheimer's disease, we investigated the effects of frondoside A, a well-known sea cucumber <i>Cucumaria frondosa</i> saponin with anti-cancer activity, on A aggregation and proteotoxicity. The results showed that frondoside A at a low concentration of 1 M significantly delayed the worm paralysis caused by A aggregation as compared with control group. In addition, the number of A plaque deposits in transgenic worm tissues was significantly decreased. Frondoside A was more effective in these activities than ginsenoside-Rg3, a comparable ginseng saponin. Immunoblot analysis revealed that the level of small oligomers as well as various high molecular weights of A species in the transgenic <i>C. elegans</i> were significantly reduced upon treatment with frondoside A, whereas the level of A monomers was not altered. This suggested that frondoside A may primarily reduce the level of small oligomeric forms, the most toxic species of A. Frondoside A also protected the worms from oxidative stress and rescued chemotaxis dysfunction in a transgenic strain whose neurons express A. Taken together, these data suggested that low dose of frondoside A could protect against A-induced toxicity by primarily suppressing the formation of A oligomers. Thus, the molecular mechanism of how frondoside A exerts its anti-A aggregation should be studied and elucidated in the future.