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Int Rev Cell Mol Biol,
2012]
In a variety of cell types in plants, animals, and fungi, ribonucleoprotein (RNP) complexes play critical roles in regulating RNA metabolism. These RNP granules include processing bodies and stress granules that are found broadly across cell types, as well as RNP granules unique to the germline, such as P granules, polar granules, sponge bodies, and germinal granules. This review focuses on RNP granules localized in oocytes of the major model systems, Caenorhabditis elegans, Drosophila, Xenopus, mouse, and zebrafish. The signature families of proteins within oocyte RNPs include Vasa and other RNA-binding proteins, decapping activators and enzymes, Argonaute family proteins, and translation initiation complex proteins. This review describes the many recent insights into the dynamics and functions of RNP granules, including their roles in mRNA degradation, mRNA localization, translational regulation, and fertility. The roles of the cytoskeleton and cell organelles in regulating RNP granule assembly are also discussed.
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Biochem Cell Biol,
1999]
The Ro ribonucleoprotein complex (Ro RNP) was initially described as an autoimmune target in human diseases such as systemic lupus erythematosus and Sjogren's syndrome. In Xenopus and human cells, its general structure is composed of one major protein of 60 kDa, Ro60, that binds to one of four small RNA molecules, designated Y RNAs. Although no function has been assigned to the Ro RNP, Ro60 has been shown to bind mutant 5S ribosomal RNA (rRNA) molecules in Xenopus oocytes, suggesting a role for Ro60 in 5S rRNA biogenesis. Ro60 has also been shown to participate in the regulation of the translational fate of the L4 ribosomal protein mRNA by interacting with the 5' untranslated region, again suggesting its possible implication in ribosome biogenesis. To identify the function of Ro RNP, we have taken a genetic approach in the nematode Caenorhabditis elegans. As such, we characterized the gene encoding the protein ROP-1, the homologue of the human Ro60 protein. Here, we review the phenotypic analysis of C. elegans rop-l(-) mutants and integrate these results into a model for the function of the Ro RNP particle.
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Trends Cell Biol,
2009]
Development requires the translation of stored maternal messenger RNAs (mRNAs) in a spatial and temporally specified manner. Maternal mRNAs are often in large RNA-protein (RNP) granules. Recent papers reveal that maternal mRNA granules in Caenorhabditis elegans oocytes and early development are dynamic and related to P-bodies and stress granules, which are conserved RNP granules seen in somatic cells. In addition, a highly conserved putative RNA helicase, termed CGH-1 in C. elegans, is now shown to be important for both for translation repression and the stability of stored mRNAs. The analysis of CGH-1 ortholog functions in somatic cells and its interacting proteins indicate possible mechanisms by which this protein family might stabilize stored maternal mRNAs.
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Mol Cell Endocrinol,
2009]
Germline cells of many animals possess characteristic cytoplasmic structures termed germinal granules or nuage. Germinal granules are ribonucleoprotein (RNP) amorphous aggregates lacking limiting membranes, and their molecular composition is evolutionarily conserved in divergent species. Studies on germinal granules in several model animals, such as Drosophila, C. elegans and Xenopus, have mainly focused on the asymmetric partitioning of the structures to prospective germ cells during early embryogenesis. In mammals, on the other hand, germinal granules become discernible at later stages of germ cell differentiation, such as in spermatogenesis and oogenesis. Interestingly, recent genetic studies indicate that germinal granule components in mice function primarily in postnatal germ cell differentiation in the male, but not in early embryonic stages. While the function(s) of germinal granules shared by divergent species and at different differentiation stages of the germline remain elusive, evidence is accumulating that the characteristic RNP is associated with RNA metabolism, retrotransposon regulation and interplay with mitochondria. Here, we present a brief overview of the structural and molecular characteristics of mammalian germinal granules.
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Genetics,
2022]
The transparency of Caenorhabditis elegans provides a unique window to observe and study the function of germ granules. Germ granules are specialized ribonucleoprotein (RNP) assemblies specific to the germline cytoplasm, and they are largely conserved across Metazoa. Within the germline cytoplasm, they are positioned to regulate mRNA abundance, translation, small RNA production, and cytoplasmic inheritance to help specify and maintain germline identity across generations. Here we provide an overview of germ granules and focus on the significance of more recent observations that describe how they further demix into sub-granules, each with unique compositions and functions.
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Wiley Interdiscip Rev RNA,
2021]
Ribonucleoprotein (RNP) granules are no newcomers in biology. Found in all life forms, ranging across taxa, these membrane-less "organelles" have been classified into different categories based on their composition, structure, behavior, function, and localization. Broadly, they can be listed as stress granules (SGs), processing bodies (PBs), neuronal granules (NGs), and germ cell granules (GCGs). Keeping in line with the topic of this review, RNP granules present in the germ cells have been implicated in a wide range of cellular functions including cellular specification, differentiation, proliferation, and so forth. The mechanisms used by them can be diverse and many of them remain partly obscure and active areas of research. GCGs can be of different types in different organisms and at different stages of development, with multiple types coexisting in the same cell. In this review, the different known subcategories of GCGs have been studied with respect to five distinct model organisms, namely, Drosophila, Caenorhabditis elegans, Xenopus, Zebrafish, and mammals. Of them, the cytoplasmic polar granules in Drosophila, P granules in C. elegans, balbiani body in Xenopus and Zebrafish, and chromatoid bodies in mammals have been specifically emphasized upon. A descriptive account of the same has been provided along with insights into our current understanding of their functional significance with respect to cellular events relating to different developmental and reproductive processes. This article is categorized under: RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Export and Localization > RNA Localization RNA in Disease and Development > RNA in Disease.
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J Androl,
2009]
Germ granules are large, non-membrane-bound, ribonucleoprotein (RNP) organelles found in the germ line cytoplasm of most, if not all, animals. The term germ granule is synonymous with the perinuclear nuage in mouse and human germ cells. These large RNPs are complexed with germ line-specific cytoplasmic structures such as the mitochondrial cloud, intermitochondrial cement, and chromatoid bodies. The widespread presence of germ granules across species and the associated germ line defects when germ granules are compromised suggest that germ granules are key determinants of the identity and special properties of germ cells. The nematode Caenorhabditis elegans has been a very fruitful model system for the study of germ granules, wherein they are referred to as P granules. P granules contain a heterogeneous mixture of RNAs and proteins. To date, most of the known germ granule proteins across species, and all of the known P granule components in C elegans, are associated with RNA metabolism, which suggests that a main function of germ granules is posttranscriptional regulation. Here we review P granule structure and localization, P granule composition, the genetic pathway of P granule assembly, and the consequences in the germ line when P granule components are lost. The findings in C elegans have important implications for the germ granule function during postnatal germ cell differentiation in mammals.