Nucleolar Research Articles

DEAD-box RNA helicase 10 is required for 18S rRNA maturation by controlling the release of U3 snoRNA from pre-rRNA in embryonic stem cells

Ribosome biogenesis plays a pivotal role in maintaining stem cell homeostasis, yet the precise regulatory mechanisms governing this process in mouse embryonic stem cells (mESCs) remain largely unknown. In this investigation, we ascertain that DEAD-box RNA helicase 10 (DDX10) is indispensable for upholding cellular homeostasis and the viability of mESCs. Positioned predominantly at the nucleolar dense fibrillar component (DFC) and granular component (GC), DDX10 predominantly binds to 45S ribosomal RNA (rRNA) and orchestrates ribosome biogenesis. Degradation of DDX10 prevents the release of U3 snoRNA from pre-rRNA, leading to perturbed pre-rRNA processing and compromised maturation of the 18S rRNA, thereby disrupting the biogenesis of the small ribosomal subunit. Moreover, DDX10 participates in the process of liquid-liquid phase separation (LLPS), which is necessary for efficient ribosome biogenesis. Notably, the NUP98-DDX10 fusion associated with acute myelocytic leukemia (AML) alters the cellular localization of DDX10 and results in loss of ability to regulate pre-rRNA processing. Collectively, this study reveals the critical role of DDX10 as a pivotal regulator of ribosome biogenesis in mESCs.

Bioinspired peptide sensors with tailorable structure for specific and in-situ tracking of Hg2+ biodistribution in living cells upon acute exposure

Metal-biomolecule interactions that are ubiquitous in nature provide fundamental knowledge and rich structural motifs for the development of functional molecules and smart sensors. In this work, inspired by the active sites in metalloproteins, a biomimetic peptide sensor was designed for the selective recognition and activatable sensing of Hg2+ in living biosystems. Tetraphenylethylene (TPE) with typical aggregation-induced emission (AIE) behavior, was introduced as the activatable signal transducer to enable high signal-to-background signaling. The tailorable side chains and flexible peptide linkage were exploited to tune the coordination affinity, selectivity, and fluorescence response toward Hg2+. Benefiting from the rapid response (1 min), high specificity and nanomolar sensitivity, the peptide sensor allows investigating the mechanism of acute toxicity of Hg2+. Capable of penetrating plasma membrane, the peptide sensor revealed the dosage-dependent and dynamic subcellular biodistribution behavior of Hg2+. The finding that Hg2+ preferentially accumulates and rapidly enriches in nucleoli of cells upon short exposure, evidences the adverse effect toward ribosome biogenesis and the resultant genetic deficiencies. These results highlight the peptide sensors as promising tools for not only on-site detection, but also studying the cell biology and toxicology of this metal ion in living biosystems.

Piwi mutant germ cells transmit a form of heritable stress that promotes longevity.

The C. elegans Argonaute protein PRG-1/Piwi and associated piRNAs protect metazoan genomes by silencing transposons and other types of foreign DNA. As prg-1 mutants are propagated, their fertility deteriorates prior to the onset of a reproductive arrest phenotype that resembles a starvation-induced stress response. We found that late-generation prg-1 mutants with substantially reduced fertility were long-lived, whereas early- or mid-generation prg-1 mutants had normal lifespans. Loss of the stress response transcription factor DAF-16 caused mid- or late-generation prg-1 mutants to live very short lives, whereas overexpression of DAF-16 enabled both mid- and late-generation prg-1 mutants to live long. Cytoplasmic P-bodies that respond to stress increased in long-lived late-generation prg-1 mutants and were transmitted to F1 but not F2 cross-progeny. Moreover, moderate levels of heritable stress shorten late-generation prg-1 mutant longevity when DAF-16 or P bodies are deficient. Together, these results suggest that the longevity of late-generation prg-1 mutants is a hormetic stress response. However, dauer larvae that occur in response to stress were not observed in late-generation prg-1 mutants. Small germ cell nucleoli that depended on germline DAF-16 were present in late-generation prg-1 mutants but were not necessary for their longevity. We propose that prg-1 mutant germ cells transmit a form of heritable stress, high levels of which promote longevity and strongly reduce fertility. The heritable stress transmitted by prg-1/Piwi mutant germ cells may be generally relevant to epigenetic inheritance of longevity.

Single-shot quantitative differential phase contrast microscope using a single calcite beam displacer

This paper presents the development of a single-shot, partially spatially coherent quantitative differential phase contrast microscopy (Q-DPCM) system. The optical scheme comprises a polarizer, lenses, calcite beam displacer, and analyzer, which can be seamlessly integrated to an existing bright-field microscopy system, transforming it into a Q-DPCM system. It utilizes a partially spatially coherent light source, enabling single-shot quantitative differential phase recovery of the specimens with high spatial phase sensitivity. It generates highly sensitive quantitative differential phase images of the specimens along one direction, like a gradient light interference microscopy (GLIM) system, using only a single interferogram. First, we validated the differential phase measurement capability of the system through experiments on polystyrene spheres (diameter 5.2 µm) and HeLa cells. Next, the system is utilized to generate quantitative phase maps of human red blood cells using two orthogonal differential interferograms recorded at two orientations of the calcite beam displacer. Further, the Q-DPCM system is implemented for 1-h time-lapse live cell monitoring, revealing the dynamics of intracellular granules such as nucleolus and lipids in U2OS cells.

Spatiotemporal protein interactome profiling through condensation-enhanced photocrosslinking.

Resolving protein-protein interactions (PPIs) inside biomolecular condensates is crucial for elucidating their functions and regulation mechanisms. The transient nature of condensates and the multiple localizations of clients, however, have rendered it challenging to determine compartment-specific PPIs. Here we developed a condensation-enhanced, spatially directed, metabolic incorporation-assisted photocrosslinking strategy-termed DenseMAP-for spatiotemporally resolved dissection of the direct protein interactome within condensates. By leveraging our condensation-enhanced photocrosslinker and the spatially directed biotin tagging, DenseMAP enabled stress-granule-specific interactome mapping of the N6-methyladenosine readers YTHDF1 and YTHDF2, and uncovered the functional role of phosphorylation on the SARS-CoV-2 nucleocapsid protein in regulating virus replication. Further applying DenseMAP for direct interactome mapping of the subcompartmental scaffold protein NPM1 deciphered nucleolar granular component proteome, and unveiled the critical role of SUMOylation in controlling nucleolar proteome homeostasis. DenseMAP provides a platform technology for analysing functional PPI networks within subcellular and subcompartmental condensates under diverse physiological and/or pathological settings.

Cervic cancer classification using quantum fuzzy set

In this sophisticated world living with CIN cervic cancer is much jeopardy. Cancer is a stochastic (random) process. So, in that CIN in initial stage is not jeopardy. It is totally because of hazardous malign cells. Using its modality in image is selected in existing system only automated classification depends on input image. But in proposed methodology the innovative alludes the jeopardy of CIN cancer is found using the size of /area of nucleus or cytoplasm. This proposed methodology was developed with an algorithm to find CIN area/size. This research work establishes a Cervic Cancer Classification Using Contour Based on Area of Nucleolus and Cytoplasm in Cells (CBANC) which classifies noise spread images into any one of five phases. A similarity measure produces 90% efficiency in proposed system as par with inefficient existing system which fetches us 50%. By pragmatic application it is proved that CBANC with fuzzy is better than Baye’s. This can be accomplished by removing well distinct consistency features and choosing preeminent classifier. Proposed work can extend with 3D input images for future research. It produces mightiest parameter shape and intensity which is very essential for 3D approach. The inference of proposed system can extend the latest classifier engines for more accuracy. It can easily predict more than 90% accuracy will be there. And also derive cancer growing and after therapy for cancer shrinking algorithm will be used for 2D or 3D CIN cancer classification. The outcomes of the proposed methodology CBANC shows that better when compared to the existing methodology like Bayes. It can be implemented in the real world environments of the medical field.

Thioflavin-T: application as a neuronal body and nucleolar stain and the blue light photo enhancement effect

Thioflavin-T (THT) is a common and indispensable tool for the study of amyloid pathologies and protein aggregation, both in vitro and for histological samples. In this study we expand the use of THT beyond its canonical usage for staining amyloid plaques and demonstrate its novel use as an easy and rapid stain comparable to fluorescent Nissl staining, allowing for clear discernment of neuronal cell bodies and also nucleoli in fixed tissue and live cells. We believe that this is of value for any lab that studies central nervous system (CNS) tissues. Furthermore, we show that THT could potentially be used as a an alternative to the use of fluorescent reporters or other more costly RNA binding compounds in the study of nucleolar dynamics owing to its ability to clearly stain nucleoli in live cells. We also discovered the previously unreported effect of blue light exposure on the photo enhancement of THT excited by a 488 nm laser in stained tissue sample and how to avoid complications arising from this effect. Finally, we provide a simple protocol that can be easily adjusted either for using THT as a neuronal cell body and nucleoli stain, compatible with antibody based staining methods tested up to 4 fluorophores, or alternatively by using an additional washing step the protocol may be used for amyloid plaque detection in fixed brain tissue.

Active RNA synthesis patterns nuclear condensates.

Biomolecular condensates are membraneless compartments that organize biochemical processes in cells. In contrast to well-understood mechanisms describing how condensates form and dissolve, the principles underlying condensate patterning - including their size, number and spacing in the cell - remain largely unknown. We hypothesized that RNA, a key regulator of condensate formation and dissolution, influences condensate patterning. Using nucleolar fibrillar centers (FCs) as a model condensate, we found that inhibiting ribosomal RNA synthesis significantly alters the patterning of FCs. Physical theory and experimental observations support a model whereby active RNA synthesis generates a non-equilibrium state that arrests condensate coarsening and thus contributes to condensate patterning. Altering FC condensate patterning by expression of the FC component TCOF1 impairs ribosomal RNA processing, linking condensate patterning to biological function. These results reveal how non-equilibrium states driven by active chemical processes regulate condensate patterning, which is important for cellular biochemistry and function.

Valence-Transforming O2-Depleting Nano-Assembly Enable In Situ Tumor Depositional Embolization.

Abnormal metabolism and blood supply/O2 imbalance in tumor cells affect drug transport delivery and increase the difficulty of tumor treatment. Controlling tumor growth by inhibiting tumor cell metabolism and regulating progressive embolization in the tumor region provides an innovative basis for constructing tumor therapeutic models. A highly biocompatible and efficient O2-depleting agent has been investigated to enable in situ precipitation and embolization within the tumor microenvironment. In situ deformation embolizer, Fe-GA@CaCO3 nano-assembly (GA: gallic acid), can convert into the large granular size embolization components of Fe(III) precipitates and affluent Ca2+ within the tumor microenvironment. In situ progressive O2 depletion produces Fe(III) precipitates that embolize tumor regions, isolating O2 and nutrients by blocking supply. Meanwhile, affluent Ca2+ acts on the intracellular, causing mitochondrial dysfunction through calcium overload and contributing to irreversible tumor cell damage. Both internal and external routes work synergistically to produce precise functional inhibition of tumors from the inside out, simultaneously responding to both intracellular and the corresponding tumor regions, providing an innovative solution for anti-tumor therapy.

Nanoscale synchrotron x-ray analysis of intranuclear iron in melanised neurons of Parkinson’s substantia nigra

Neuromelanin-pigmented neurons of the substantia nigra are selectively lost during the progression of Parkinson’s disease. These neurons accumulate iron in the disease state, and iron-mediated neuron damage is implicated in cell death. Animal models of Parkinson’s have evidenced iron loading inside the nucleoli of nigral neurons, however the nature of intranuclear iron deposition in the melanised neurons of the human substantia nigra is not understood. Here, scanning transmission x-ray microscopy (STXM) is used to probe iron foci in relation to the surrounding ultrastructure in melanised neurons of human substantia nigra from a confirmed Parkinson’s case. In addition to the expected neuromelanin-bound iron, iron deposits are also associated with the edge of the cell nucleolus. Speciation analysis confirms these deposits to be ferric (Fe3+) iron. The function of intranuclear iron in these cells remains unresolved, although both damaging and protective mechanisms are considered. This finding shows that STXM is a powerful label-free tool for the in situ, nanoscale chemical characterisation of both organic and inorganic intracellular components. Future applications are likely to shed new light on incompletely understood biochemical mechanisms, such as metal dysregulation and morphological changes to cell nucleoli, that are important in understanding the pathogenesis of Parkinson’s.

To the ring-shaped nucleolus seen by microscopy using human lymphocytes of blood donors and chronic lymphocytic leukemia patients.

The present study was undertaken to provide more information on the peripheral RNA containing ring of ringshaped nucleoli (RSNo). Human lymphocytes of blood donors and patients suffering from B chronic lymphocytic leukemia mostly characterized by RSNo represented very convenient cell models for such study. According to the light microscopy the peripheral RNA ring possessed several highly condensed foci. Such regions represented accumulated dense RNA fibrillar components (DFCs) seen by the electron microscopy. In contrary, the incidence of dense granular RNA-containing components (GCs) in surrounding portions of the RNA ring was small. Thus, the structural and morphological organization of the peripheral RNA ring of RSNo apparently reflects sites of micro-segregated foci of DFCs and a small incidence of GCs. That structural organization of the peripheral RNA ring of RSNo appeared to be a prerequisite for further regressive nucleolar changes resulting in the development of micronucleoli in terminal lymphocytes.

Reduced dynamicity and increased high-order protein assemblies in dense fibrillar component of the nucleolus under cellular senescence

Cellular senescence, which is triggered by various stressors, manifests as irreversible cell cycle arrest, resulting in the disruption of multiple nuclear condensates. One of the affected structures is the nucleolus, whose tripartite layout, separated into distinct liquid phases, allows for the stepwise progression of ribosome biogenesis. The dynamic properties of dense fibrillar components, a sub-nucleolar phase, are crucial for mediating pre-rRNA processing. However, the mechanistic link between the material properties of dense fibrillar components and cellular senescence remains unclear. We established a significant association between cellular senescence and alterations in nucleolar materiality and characteristics, including the number, size, and sphericity of individual subphases of the nucleolus. Senescent cells exhibit reduced fibrillarin dynamics, aberrant accumulation of high-order protein assemblies, such as oligomers and fibrils, and increased dense fibrillar component density. Intriguingly, the addition of RNA-interacting entities mirrored the diminished diffusion of fibrillarin in the nucleolus during cellular senescence. Thus, our findings contribute to a broader understanding of the intricate changes in the materiality of the nucleolus associated with cellular senescence and shed light on nucleolar dynamics in the context of aging and cellular stress.

Homeotic DUX4 Genes Shape Dynamic Inter-Chromosomal Contacts with Nucleoli in Human Cells.

Nucleoli form interchromosomal contacts with genes controlling differentiation and carcinogenesis. DUX4 genes specify transcription factor possessing two homeodomains. Previously, using Circular Chromosome Conformation Capture (4С) approach on population of cells, it was demonstrated that DUX4 gene clusters form frequent contacts with nucleoli. It was found also that these contacts are almost completely abolished after heat shock treatment. 4C approach as all ligation-mediated methods is capable to detect rather close interactions between chromatin loops in nuclei. In order to independently confirm the formation and the frequency of the contacts in single cells we used FISH approach. Here, we show that DUX genes in single cells form stable contacts in all tested HEK293T cells. During heat shock, DUX4 genes reversibly move 1-3 µm away from the nuclei. We conclude that interchromosomal contacts formed by nucleoli are strong, dynamic, and reversible, providing both the initiation and maintenance of a differentiated state.

Polyamines regulate cell fate by altering the activity of histone-modifying enzymes.

Polyamines are polycationic alkyl-amines abundant in proliferating stem and cancer cells. How these metabolites influence numerous cellular functions remains unclear. Here we show that polyamine levels decrease during differentiation and that inhibiting polyamine synthesis leads to a differentiated-like cell state. Polyamines concentrate in the nucleus and are further enriched in the nucleoli of cells in culture and in vivo . Loss of polyamines drives changes in chromatin accessibility that correlate with altered histone post-translational modifications. Polyamines interact electrostatically with DNA on the nucleosome core, stabilizing histone tails in conformations accessible to modifying enzymes. These data reveal a mechanism by which an abundant metabolite influences chromatin structure and function in a non-sequence specific manner, facilitating chromatin remodeling during reprogramming and limiting it during fate commitment.

Measurement of protein concentration in bacteria and small organelles under a light transmission microscope.

Protein concentration (PC) is an essential characteristic of cells and organelles; it determines the extent of macromolecular crowding effects and serves as a sensitive indicator of cellular health. A simple and direct way to quantify PC is provided by brightfield-based transport-of-intensity equation (TIE) imaging combined with volume measurements. However, since TIE is based on geometric optics, its applicability to micrometer-sized particles is not clear. Here, we show that TIE can be used on particles with sizes comparable to the wavelength. At the same time, we introduce a new ImageJ plugin that allows TIE image processing without resorting to advanced mathematical programs. To convert TIE data to PC, knowledge of particle volumes is essential. The volumes of bacteria or other isolated particles can be measured by displacement of an external absorbing dye ("transmission-through-dye" or TTD microscopy), and for spherical intracellular particles, volumes can be estimated from their diameters. We illustrate the use of TIE on Escherichia coli, mammalian nucleoli, and nucleolar fibrillar centers. The method is easy to use and achieves high spatial resolution.

Ribosomal DNA and Neurological Disorders.

Ribosomal DNA (rDNA) is important in the nucleolus and nuclear organization of human cells. Defective rDNA repeat maintenance has been reported to be closely associated with neurological disorders, such as Alzheimer's disease, Huntington's disease, Parkinson's disease, amyotrophic lateral sclerosis, frontotemporal dementia, depression, suicide, etc. However, there has not been a comprehensive review on the role of rDNA in these disorders. In this review, we have summarized the role of rDNA in major neurological disorders to sort out the correlation between rDNA and neurological diseases and provided insights for therapy with rDNA as a target.

Exploration of Giardia small nucleolar RNAs (snoRNAs) and their possible microRNA derivatives.

Small nucleolar RNAs (snoRNAs) are short non-coding RNAs that are abundant in the nucleoli of eukaryotic cells and play a crucial role in various aspects of ribosomal RNA (rRNA) maturation, including modifications such as 2′-O-methylation or pseudouridylation. On the other hand, Giardia duodenalis is a microaerophilic, flagellated, binucleate protozoan responsible for causing giardiasis. Although numerous snoRNAs have been detected in Giardia, their investigation remains limited. Nevertheless, they have been found to play a crucial role in the rRNA precursor processing pathway and influence other cellular functions. In addition, it has been proposed that some microRNAs are generated from these snoRNAs through excision by the Giardia endoribonuclease Dicer. These microRNAs are believed to contribute to the regulation of antigenic variation, which allows the parasite to evade the host immune response. Specifically, they play a role in modulating variant-specific surface proteins (VSPs) and other cysteine-rich surface antigens (CSAs). The main objective of this study was to bring together the available data on snoRNAs in Giardia, uncovering their functions in various processes and their importance on a global scale. In addition, the research delved into potential microRNAs speculated to originate from snoRNAs, exploring their impact on cellular processes.

Myosin VI in the nucleolus of neurosecretory PC12 cells: its involvement in the maintenance of nucleolar structure and ribosome organization.

We have previously shown that unconventional myosin VI (MVI), a unique actin-based motor protein, shuttles between the cytoplasm and nucleus in neurosecretory PC12 cells in a stimulation-dependent manner and interacts with numerous proteins involved in nuclear processes. Among the identified potential MVI partners was nucleolin, a major nucleolar protein implicated in rRNA processing and ribosome assembly. Several other nucleolar proteins such as fibrillarin, UBF (upstream binding factor), and B23 (also termed nucleophosmin) have been shown to interact with MVI. A bioinformatics tool predicted the presence of the nucleolar localization signal (NoLS) within the MVI globular tail domain, and immunostaining confirmed the presence of MVI within the nucleolus. Depletion of MVI, previously shown to impair PC12 cell proliferation and motility, caused disorganization of the nucleolus and rough endoplasmic reticulum (rER). However, lack of MVI does not affect nucleolar transcription. In light of these data, we propose that MVI is important for nucleolar and ribosome maintenance but not for RNA polymerase 1-related transcription.

Detecting material state changes in the nucleolus by label-free digital holographic microscopy

Ribosome biogenesis is initiated in the nucleolus, a multiphase biomolecular condensate formed by liquid-liquid phase separation. The nucleolus is a powerful disease biomarker and stress biosensor whose morphology reflects function. Here we have used digital holographic microscopy (DHM), a label-free quantitative phase contrast microscopy technique, to detect nucleoli in adherent and suspension human cells. We trained convolutional neural networks to detect and quantify nucleoli automatically on DHM images. Holograms containing cell optical thickness information allowed us to define a novel index which we used to distinguish nucleoli whose material state had been modulated optogenetically by blue-light-induced protein aggregation. Nucleoli whose function had been impacted by drug treatment or depletion of ribosomal proteins could also be distinguished. We explored the potential of the technology to detect other natural and pathological condensates, such as those formed upon overexpression of a mutant form of huntingtin, ataxin-3, or TDP-43, and also other cell assemblies (lipid droplets). We conclude that DHM is a powerful tool for quantitatively characterizing nucleoli and other cell assemblies, including their material state, without any staining.

Biomolecular condensates form spatially inhomogeneous network fluids.

The functions of biomolecular condensates are thought to be influenced by their material properties, and these will be determined by the internal organization of molecules within condensates. However, structural characterizations of condensates are challenging, and rarely reported. Here, we deploy a combination of small angle neutron scattering, fluorescence recovery after photobleaching, and coarse-grained molecular dynamics simulations to provide structural descriptions of model condensates that are formed by macromolecules from nucleolar granular components (GCs). We show that these minimal facsimiles of GCs form condensates that are network fluids featuring spatial inhomogeneities across different length scales that reflect the contributions of distinct protein and peptide domains. The network-like inhomogeneous organization is characterized by a coexistence of liquid- and gas-like macromolecular densities that engenders bimodality of internal molecular dynamics. These insights suggest that condensates formed by multivalent proteins share features with network fluids formed by systems such as patchy or hairy colloids.