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Perez RC, Yang X, Familari M, Martinez G, Lovicu FJ, Hime GR, de Iongh RU. TOB1 and TOB2 mark distinct RNA processing granules in differentiating lens fiber cells. J Mol Histol 2024; 55:121-138. [PMID: 38165569 DOI: 10.1007/s10735-023-10177-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Accepted: 11/12/2023] [Indexed: 01/04/2024]
Abstract
Differentiation of lens fiber cells involves a complex interplay of signals from growth factors together with tightly regulated gene expression via transcriptional and post-transcriptional regulators. Various studies have demonstrated that RNA-binding proteins, functioning in ribonucleoprotein granules, have important roles in regulating post-transcriptional expression during lens development. In this study, we examined the expression and localization of two members of the BTG/TOB family of RNA-binding proteins, TOB1 and TOB2, in the developing lens and examined the phenotype of mice that lack Tob1. By RT-PCR, both Tob1 and Tob2 mRNA were detected in epithelial and fiber cells of embryonic and postnatal murine lenses. In situ hybridization showed Tob1 and Tob2 mRNA were most intensely expressed in the early differentiating fibers, with weaker expression in anterior epithelial cells, and both appeared to be downregulated in the germinative zone of E15.5 lenses. TOB1 protein was detected from E11.5 to E16.5 and was predominantly detected in large cytoplasmic puncta in early differentiating fiber cells, often co-localizing with the P-body marker, DCP2. Occasional nuclear puncta were also observed. By contrast, TOB2 was detected in a series of interconnected peri-nuclear granules, in later differentiating fiber cells of the inner cortex. TOB2 did not appear to co-localize with DCP2 but did partially co-localize with an early stress granule marker (EIF3B). These data suggest that TOB1 and TOB2 are involved with different aspects of the mRNA processing cycle in lens fiber cells. In vitro experiments using rat lens epithelial explants treated with or without a fiber differentiating dose of FGF2 showed that both TOB1 and TOB2 were up-regulated during FGF-induced differentiation. In differentiating explants, TOB1 also co-localized with DCP2 in large cytoplasmic granules. Analyses of Tob1-/- mice revealed relatively normal lens morphology but a subtle defect in cell cycle arrest of some cells at the equator and in the lens fiber mass of E13.5 embryos. Overall, these findings suggest that TOB proteins play distinct regulatory roles in RNA processing during lens fiber differentiation.
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Affiliation(s)
- Rafaela C Perez
- Ocular Development Laboratory, Anatomy & Physiology, University of Melbourne, Parkville, VIC, 3010, Australia
| | - Xenia Yang
- Ocular Development Laboratory, Anatomy & Physiology, University of Melbourne, Parkville, VIC, 3010, Australia
| | - Mary Familari
- School of Biosciences, University of Melbourne, Parkville, VIC, 3010, Australia
| | - Gemma Martinez
- Ocular Development Laboratory, Anatomy & Physiology, University of Melbourne, Parkville, VIC, 3010, Australia
| | - Frank J Lovicu
- Molecular and Cellular Biomedicine, School of Medical Sciences and Save Sight Institute, University of Sydney, Sydney, NSW, 2006, Australia
| | - Gary R Hime
- Stem Cell Genetics Laboratory, Anatomy & Physiology, University of Melbourne, Parkville, VIC, 3010, Australia
| | - Robb U de Iongh
- Ocular Development Laboratory, Anatomy & Physiology, University of Melbourne, Parkville, VIC, 3010, Australia.
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Abstract
Ribonucleoprotein (RNP) granules are diverse membrane-less organelles that form through multivalent RNA-RNA, RNA-protein, and protein-protein interactions between RNPs. RNP granules are implicated in many aspects of RNA physiology, but in most cases their functions are poorly understood. RNP granules can be described through four key principles. First, RNP granules often arise because of the large size, high localized concentrations, and multivalent interactions of RNPs. Second, cells regulate RNP granule formation by multiple mechanisms including posttranslational modifications, protein chaperones, and RNA chaperones. Third, RNP granules impact cell physiology in multiple manners. Finally, dysregulation of RNP granules contributes to human diseases. Outstanding issues in the field remain, including determining the scale and molecular mechanisms of RNP granule function and how granule dysfunction contributes to human disease.
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Affiliation(s)
- Nina Ripin
- Department of Biochemistry and Howard Hughes Medical Institute, University of Colorado Boulder, Boulder, CO 80303, USA
| | - Roy Parker
- Department of Biochemistry and Howard Hughes Medical Institute, University of Colorado Boulder, Boulder, CO 80303, USA.
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Eichler CE, Li H, Grunberg ME, Gavis ER. Localization of oskar mRNA by agglomeration in ribonucleoprotein granules. PLoS Genet 2023; 19:e1010877. [PMID: 37624861 PMCID: PMC10484445 DOI: 10.1371/journal.pgen.1010877] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Revised: 09/07/2023] [Accepted: 07/19/2023] [Indexed: 08/27/2023] Open
Abstract
Localization of oskar mRNA to the posterior of the Drosophila oocyte is essential for abdominal patterning and germline development. oskar localization is a multi-step process involving temporally and mechanistically distinct transport modes. Numerous cis-acting elements and trans-acting factors have been identified that mediate earlier motor-dependent transport steps leading to an initial accumulation of oskar at the posterior. Little is known, however, about the requirements for the later localization phase, which depends on cytoplasmic flows and results in the accumulation of large oskar ribonucleoprotein granules, called founder granules, by the end of oogenesis. Using super-resolution microscopy, we show that founder granules are agglomerates of smaller oskar transport particles. In contrast to the earlier kinesin-dependent oskar transport, late-phase localization depends on the sequence as well as on the structure of the spliced oskar localization element (SOLE), but not on the adjacent exon junction complex deposition. Late-phase localization also requires the oskar 3' untranslated region (3' UTR), which targets oskar to founder granules. Together, our results show that 3' UTR-mediated targeting together with SOLE-dependent agglomeration leads to accumulation of oskar in large founder granules at the posterior of the oocyte during late stages of oogenesis. In light of previous work showing that oskar transport particles are solid-like condensates, our findings indicate that founder granules form by a process distinct from that of well-characterized ribonucleoprotein granules like germ granules, P bodies, and stress granules. Additionally, they illustrate how an individual mRNA can be adapted to exploit different localization mechanisms depending on the cellular context.
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Affiliation(s)
- Catherine E. Eichler
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Hui Li
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Michelle E. Grunberg
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America
| | - Elizabeth R. Gavis
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America
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Chukrallah LG, Snyder EM. Modern tools applied to classic structures: Approaches for mammalian male germ cell RNA granule research. Andrology 2023; 11:872-883. [PMID: 36273399 DOI: 10.1111/andr.13320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Revised: 09/20/2022] [Accepted: 10/10/2022] [Indexed: 11/28/2022]
Abstract
First reported in the 1800s, germ cell granules are small nonmembrane bound RNA-rich regions of the cytoplasm. These sites of critical RNA processing and storage in the male germ cell are essential for proper differentiation and development and are present in a wide range of species from Caenorhabditis elegans through mammals. Initially characterized by light and electron microscopy, more modern techniques such as immunofluorescence and genetic models have played a major role in expanding our understanding of the composition of these structures. While these methods have given light to potential granule functions, much work remains to be done. The current expansion of imaging technologies and omics-scale analyses to germ cell granule research will drive the field forward considerably. Many of these methods, both current and upcoming, have considerable caveats and limitations that necessitate a holistic approach to the study of germ granules. By combining and balancing different techniques, the field is poised to elucidate the nature of these critical structures.
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Affiliation(s)
- Lauren G Chukrallah
- Department of Animal Science, Rutgers, the State University of New Jersey, New Brunswick, New Jersey, USA
| | - Elizabeth M Snyder
- Department of Animal Science, Rutgers, the State University of New Jersey, New Brunswick, New Jersey, USA
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Grzejda D, Mach J, Schweizer JA, Hummel B, Rezansoff AM, Eggenhofer F, Panhale A, Lalioti ME, Cabezas Wallscheid N, Backofen R, Felsenberg J, Hilgers V. The long noncoding RNA mimi scaffolds neuronal granules to maintain nervous system maturity. Sci Adv 2022; 8:eabo5578. [PMID: 36170367 PMCID: PMC9519039 DOI: 10.1126/sciadv.abo5578] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Accepted: 08/15/2022] [Indexed: 05/29/2023]
Abstract
RNA binding proteins and messenger RNAs (mRNAs) assemble into ribonucleoprotein granules that regulate mRNA trafficking, local translation, and turnover. The dysregulation of RNA-protein condensation disturbs synaptic plasticity and neuron survival and has been widely associated with human neurological disease. Neuronal granules are thought to condense around particular proteins that dictate the identity and composition of each granule type. Here, we show in Drosophila that a previously uncharacterized long noncoding RNA, mimi, is required to scaffold large neuronal granules in the adult nervous system. Neuronal ELAV-like proteins directly bind mimi and mediate granule assembly, while Staufen maintains condensate integrity. mimi granules contain mRNAs and proteins involved in synaptic processes; granule loss in mimi mutant flies impairs nervous system maturity and neuropeptide-mediated signaling and causes phenotypes of neurodegeneration. Our work reports an architectural RNA for a neuronal granule and provides a handle to interrogate functions of a condensate independently of those of its constituent proteins.
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Affiliation(s)
- Dominika Grzejda
- Max-Planck-Institute of Immunobiology and Epigenetics, Freiburg 79108, Germany
- Faculty of Biology, Albert Ludwig University of Freiburg, Freiburg 79104, Germany
- International Max Planck Research School for Molecular and Cellular Biology (IMPRS- MCB), Freiburg 79108, Germany
| | - Jana Mach
- Max-Planck-Institute of Immunobiology and Epigenetics, Freiburg 79108, Germany
| | - Johanna Aurelia Schweizer
- Friedrich Miescher Institute for Biomedical Research (FMI), Basel 4058, Switzerland
- University of Basel, Basel 4001, Switzerland
| | - Barbara Hummel
- Max-Planck-Institute of Immunobiology and Epigenetics, Freiburg 79108, Germany
| | | | - Florian Eggenhofer
- Department of Computer Science, Albert Ludwig University of Freiburg, Freiburg 79110, Germany
| | - Amol Panhale
- Max-Planck-Institute of Immunobiology and Epigenetics, Freiburg 79108, Germany
| | - Maria-Eleni Lalioti
- Max-Planck-Institute of Immunobiology and Epigenetics, Freiburg 79108, Germany
| | | | - Rolf Backofen
- Department of Computer Science, Albert Ludwig University of Freiburg, Freiburg 79110, Germany
- BIOSS and CIBSS Centres for Biological Signalling Studies, University of Freiburg, Freiburg 79104, Germany
| | - Johannes Felsenberg
- Friedrich Miescher Institute for Biomedical Research (FMI), Basel 4058, Switzerland
| | - Valérie Hilgers
- Max-Planck-Institute of Immunobiology and Epigenetics, Freiburg 79108, Germany
- CIBSS Centre for Integrative Biological Signalling Studies, University of Freiburg, Freiburg 79104, Germany
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Jeon P, Ham HJ, Park S, Lee JA. Regulation of Cellular Ribonucleoprotein Granules: From Assembly to Degradation via Post-translational Modification. Cells 2022; 11:cells11132063. [PMID: 35805146 PMCID: PMC9265587 DOI: 10.3390/cells11132063] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Revised: 06/09/2022] [Accepted: 06/24/2022] [Indexed: 02/04/2023] Open
Abstract
Cells possess membraneless ribonucleoprotein (RNP) granules, including stress granules, processing bodies, Cajal bodies, or paraspeckles, that play physiological or pathological roles. RNP granules contain RNA and numerous RNA-binding proteins, transiently formed through the liquid–liquid phase separation. The assembly or disassembly of numerous RNP granules is strongly controlled to maintain their homeostasis and perform their cellular functions properly. Normal RNA granules are reversibly assembled, whereas abnormal RNP granules accumulate and associate with various neurodegenerative diseases. This review summarizes current studies on the physiological or pathological roles of post-translational modifications of various cellular RNP granules and discusses the therapeutic methods in curing diseases related to abnormal RNP granules by autophagy.
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