中川 真一 (NAKAGAWA, Shinichi)

中川 真一 (NAKAGAWA, Shinichi)

理化学研究所 中川RNA生物学研究室 准主任研究員
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NEAT1_2 long noncoding RNA (lncRNA) is the molecular scaffold of paraspeckle nuclear bodies. Here, we report an improved RNA extraction method: extensive needle shearing or heating of cell lysate in RNA extraction reagent improved NEAT1_2 extraction by 20‐fold (a property we term “semi‐extractability”), whereas using a conventional method NEAT1_2 was trapped in the protein phase. The improved extraction method enabled us to estimate that approximately 50 NEAT1_2 molecules are present in a single paraspeckle. Another architectural lncRNA, IGS16, also exhibited similar semi‐extractability. A comparison of RNA‐seq data from needle‐sheared and control samples revealed the existence of multiple semi‐extractable RNAs, many of which were localized in subnuclear granule‐like structures. The semi‐extractability of NEAT1_2 correlated with its association with paraspeckle proteins and required the prion‐like domain of the RNA‐binding protein FUS. This observation suggests that tenacious RNA–protein and protein–protein interactions, which drive nuclear body formation, are responsible for semi‐extractability. Our findings provide a foundation for the discovery of the architectural RNAs that constitute nuclear bodies.

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Paraspeckles are nuclear bodies built on the long noncoding RNA Neat1, which regulates a variety of physiological processes including cancer progression and corpus luteum formation. To obtain further insight into the molecular basis of the function of paraspeckles, we performed fine structural analyses of these nuclear bodies using structural illumination microscopy. Notably, paraspeckle proteins are found within different layers along the radially arranged bundles of Neat1 transcripts, forming a characteristic core-shell spheroidal structure. In cells lacking the RNA binding protein Fus, paraspeckle spheroids are disassembled into smaller particles containing Neat1, which are diffusely distributed in the nucleoplasm. Sequencing analysis of RNAs purified from paraspeckles revealed that AG-rich transcripts associate with Neat1, which are distributed along the shell of the paraspeckle spheroids. We propose that paraspeckles sequester core components inside the spheroids, whereas the outer surface associates with other components in the nucleoplasm to fulfill their function.

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The long noncoding RNA Gomafu/MIAT/Rncr2 is thought to function in retinal cell specification, stem cell differentiation and the control of alternative splicing. To further investigate physiological functions of Gomafu, we created mouse knockout (KO) model that completely lacks the Gomafu gene. The KO mice did not exhibit any developmental deficits. However, behavioral tests revealed that the KO mice are hyperactive. This hyperactive behavior was enhanced when the KO mice were treated with the psychostimulant methamphetamine, which was associated with an increase in dopamine release in the nucleus accumbens. RNA sequencing analyses identified a small number of genes affected by the deficiency of Gomafu, a subset of which are known to have important neurobiological functions. These observations suggest that Gomafu modifies mouse behavior thorough a mild modulation of gene expression and/or alternative splicing of target genes.

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This special issue aims to assemble available knowledge on long noncoding RNAs (lncRNAs) and provide future research directions for discovering the molecular functions of this emerging family of molecules. The genomes of eukaryotes, particularly mammalian species including human and mouse, possess large chunks of nonprotein-coding regions. Only 2% of the human genome is dedicated to coding for proteins; the remainder is constituted of noncoding regions, which are for the most part functionally unannotated. At the beginning of the postgenomic era, transcriptome genome-wide analyses in various organisms unexpectedly revealed that large portions of the mammalian genome produce numerous transcripts that lack protein-coding potential. Among these RNAs, noncoding transcripts longer than 200 nt are arbitrary referred to as “lncRNAs”. Many lncRNAs are expressed at low levels, exhibit tissue- or cell type specific expression patterns, and are not as well conserved between species as protein-coding mRNAs. LncRNAs share common features with protein-coding mRNAs; for instance, with few exceptions, they are transcribed by RNA polymerase II, possess the canonical cap structure at their 5′ termini, and their 3′ termini are polyadenylated. Nevertheless, many lncRNAs are not subject to nuclear export and function within the nucleus, which is in sharp contrast to mRNAs that are transported to the cytoplasm and translated into proteins. Notably, a group of lncRNAs, once classified as lncRNAs, have now been found to encode small polypeptides, making it necessary to establish new methods to distinguish lncRNAs from polypeptide-coding RNAs...

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A number of non-membranous cellular bodies have been identified in higher eukaryotes, and these bodies contain a specific set of proteins and RNAs that are used to fulfill their functions. The size of these RNA-containing cellular bodies is usually on a submicron scale, making it difficult to observe fine structures using optical microscopy due to the diffraction limitation of visible light. Recently, microscope companies have released super-resolution microscopes that were developed using different principles, enabling the observation of sub-micron structures not resolvable in conventional fluorescent microscopy. Here, we describe multi-color fluorescent in situ hybridization techniques optimized for the simultaneous detection of RNA and proteins using super-resolution microscopy, namely structured illumination microscopy (SIM).

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Short interspersed elements (SINEs) comprise a significant portion of mammalian genomes and regulate gene expression through a variety of mechanisms. Here, we show that Myodonta clade-specific 4.5S RNAH (4.5SH), an abundant nuclear noncoding RNA that is highly homologous to the retrotransposon SINE B1, controls the expression of reporter gene that contains the antisense insertion of SINE B1 via nuclear retention. The depletion of endogenous 4.5SH with antisense oligonucleotides neutralizes the nuclear retention and changes the subcellular distribution of the reporter transcripts containing the antisense SINE B1 insertion. Importantly, endogenous transcripts with antisense SINE B1 were increased in the cytoplasm after knockdown of 4.5SH, leading to a decrease in cellular growth. We propose a tentative hypothesis that the amplification of the 4.5SH cluster in specific rodent species might delineate their evolutionary direction via the regulation of genes containing the antisense insertion of SINE B1.

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This volume focuses on cytological, biochemical, and molecular biological methods to identify and examine the function of each nuclear body, with an emphasis on the analysis of long non-coding RNAs. Chapters focus on exploring recent studies that reveal how certain long non protein-coding RNAs accumulate in specific nuclear bodies and regulate the function of the bodies by serving as architectural components or controlling the dynamics of associating protein components. Written in the highly successful Methods of Molecular Biology series format, chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible laboratory protocols, and key tips on troubleshooting and avoiding known pitfalls.

Authoritative and practical, Nuclear Bodies and Noncoding RNAs: Methods and Protocols serves as a guideline for further study into the sophisticated regulation of gene expression.

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Neat1 is a non-protein-coding RNA that serves as an architectural component of the nuclear bodies known as paraspeckles. Although cell-based studies indicate that Neat1 is a crucial regulator of gene expression, its physiological relevance remains unclear. Here, we find that Neat1 knockout (KO) mice stochastically fail to become pregnant despite normal ovulation. Unilateral transplantation of wild-type ovaries or the administration of progesterone partially rescued the phenotype, suggesting that corpus luteum dysfunction and concomitant low progesterone were the primary causes of the decreased fertility. In contrast to the faint expression observed in most of the adult tissues, Neat1 was highly expressed in the corpus luteum, and the formation of luteal tissue was severely impaired in nearly half of the Neat1 KO mice. These observations suggest that Neat1 is essential for the formation of the corpus luteum and for the subsequent establishment of pregnancy under a suboptimal condition that has not yet been identified.

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