Nucleolar Dynamics Research Articles

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.

Dynamic Mitotic Localization of the Centrosomal Kinases CDK1, Plk, AurK, and Nek2 in Dictyostelium amoebae.

The centrosome of the amoebozoan model Dictyostelium discoideum provides the best-established model for an acentriolar centrosome outside the Opisthokonta. Dictyostelium exhibits an unusual centrosome cycle, in which duplication is initiated only at the G2/M transition and occurs entirely during the M phase. Little is known about the role of conserved centrosomal kinases in this process. Therefore, we have generated knock-in strains for Aurora (AurK), CDK1, cyclin B, Nek2, and Plk, replacing the endogenous genes with constructs expressing the respective green fluorescent Neon fusion proteins, driven by the endogenous promoters, and studied their behavior in living cells. Our results show that CDK1 and cyclin B arrive at the centrosome first, already during G2, followed by Plk, Nek2, and AurK. Furthermore, CDK1/cyclin B and AurK were dynamically localized at kinetochores, and AurK in addition at nucleoli. The putative roles of all four kinases in centrosome duplication, mitosis, cytokinesis, and nucleolar dynamics are discussed.

The yeast VAPs Scs2 and Scs22 are required for NVJ integrity and micronucleophagy

Microautophagy degrades cargos in the vacuole by direct engulfment of the vacuolar membrane. Micronucleophagy selectively degrades a portion of the nucleus in budding yeast. The vacuole contacts the nucleus via the nucleus–vacuole junction (NVJ), and in micronucleophagy a portion of the nucleus containing nucleolar proteins is made to protrude into the vacuole at the NVJ, followed by abscission and degradation. Microautophagy and micronucleophagy are induced by inactivation of target of rapamycin complex 1 (TORC1) protein kinase after nutrient starvation. Here, we show that the VAMP-associated proteins (VAPs) Scs2 and its paralog Scs22 are required for NVJ integrity and micronucleophagic degradation of nucleolar proteins. On the other hand, nucleolar dynamics prerequisite for micronucleophagy were not impaired in VAP mutant cells. Finally, yeast VAPs were critical for viability during prolonged nutrient starvation. This study sheds light on the emerging role of VAP in adaptation in responses to nutrient starvation.

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.

Prostate epithelial cell intrinsic C3 represses MYC-driven tumorigenesis

Abstract The synthesis of complement component C3 within the tumor microenvironment has been implicated as a pivotal modulator in oncogenesis and is emerging as an attractive therapeutic target. Historically, tumor-infiltrating immune cells have been recognized as principal contributors to intra-tumoral C3, with resultant activation fragments primarily facilitating tumor progression via immunosuppression and induction of angiogenesis. Despite the ubiquity of C3 expression in neoplastic tissues, the implications of cancer cell autonomous C3 during oncogenesis remain inadequately characterized. Here we show that loss of steady-state, endogenous C3 expression, C3a generation, and C3a receptor engagement in human prostate epithelial cells (PECs) mark a salient transition towards malignancy. We reveal that tonic intrinsic C3a-C3aR engagement in non-transformed PECs serves to restrain phosphoinositide 3-kinase delta activity, which inhibits the oncogenic MYC cascade and MYC-driven ribosomal biogenesis and nucleolar dynamics to maintain normal cell homeostasis. Further, comprehensive analyses show that C3 transcript and C3 protein levels are widely suppressed across human prostate cancers. Collectively, these findings ascribe a non-traditional, tumor-suppressor function to cell intrinsic C3 and advocate for dissection of the context-specific roles of complement, a strategy that may inform the development of targeted cancer therapies.

Polyamine Dysregulation and Nucleolar Disruption in Alzheimer's Disease.

A hypothesis of Alzheimer's disease etiology is proposed describing how cellular stress induces excessive polyamine synthesis and recycling which can disrupt nucleoli. Polyamines are essential in nucleolar functions, such as RNA folding and ribonucleoprotein assembly. Changes in the nucleolar pool of anionic RNA and cationic polyamines acting as counterions can cause significant nucleolar dynamics. Polyamine synthesis reduces S-adenosylmethionine which, at low levels, triggers tau phosphorylation. Also, polyamine recycling reduces acetyl-CoA needed for acetylcholine, which is low in Alzheimer's disease. Extraordinary nucleolar expansion and/or contraction can disrupt epigenetic control in peri-nucleolar chromatin, such as chromosome 14 with the presenilin-1 gene; chromosome 21 with the amyloid precursor protein gene; chromosome 17 with the tau gene; chromosome 19 with the APOE4 gene; and the inactive X chromosome (Xi; aka "nucleolar satellite") with normally silent spermine synthase (polyamine synthesis) and spermidine/spermine-N1-acetyltransferase (polyamine recycling) alleles. Chromosomes 17, 19 and the Xi have high concentrations of Alu elements which can be transcribed by RNA polymerase III if positioned nucleosomes are displaced from the Alu elements. A sudden flood of Alu RNA transcripts can competitively bind nucleolin which is usually bound to Alu sequences in structural RNAs that stabilize the nucleolar heterochromatic shell. This Alu competition leads to loss of nucleolar integrity with leaking of nucleolar polyamines that cause aggregation of phosphorylated tau. The hypothesis was developed with key word searches (e.g., PubMed) using relevant terms (e.g., Alzheimer's, lupus, nucleolin) based on a systems biology approach and exploring autoimmune disease tautology, gaining synergistic insights from other diseases.

Anomalous coarsening of coalescing nucleoli in human cells

Coarsening is a ubiquitous phenomenon in droplet systems near thermodynamic equilibrium—as an increase in droplet size lowers the system’s free energy—however, coarsening of droplets in nonequilibrium systems, such as the cell nucleus, is far from understood. Liquid condensates in the cell nucleus, like nucleoli, form by liquid-liquid phase separation and play a key role in the nuclear organization. In human cells, nucleolar droplets are nucleated at the beginning of the cell cycle and coarsen with time by coalescing with each other. Upon coarsening, human nucleoli exhibit an anomalous volume distribution P(V)∼V−1, which cannot be explained by any existing theory. In this work, we investigate physical mechanisms behind the anomalous coarsening of human nucleoli. Using spinning disk confocal microscopy, we simultaneously record dynamic behavior of nucleoli and their surrounding chromatin before their coalescence in live human cells. We find that nucleolar anomalous coarsening persists during the entire cell cycle. We measure chromatin flows and density between and around nucleoli, as well as relative motion of two nucleoli before they coalesce. We find that, before nucleolar coalescence, chromatin concentration decreases in the space between nucleoli and the nucleoli move faster toward each other, resembling an effective depletion attraction between the coalescing nucleoli. Indeed, our computational simulations of nucleolar dynamics show that short-ranged attraction is sufficient to explain the observed anomalous volume distribution of human nucleoli. Overall, our results reveal a potential physical mechanism contributing to coarsening of human nucleoli. Such knowledge expands our picture of the physical behavior of liquid condensates inside the cell nucleus and our understanding of the dynamic nuclear organization.

NOC1 is a direct MYC target, and its protein interactome dissects its activity in controlling nucleolar function.

The nucleolus is a subnuclear compartment critical in ribosome biogenesis and cellular stress responses. These mechanisms are governed by a complex interplay of proteins, including NOC1, a member of the NOC family of nucleolar proteins responsible for controlling rRNA processing and ribosomal maturation. This study reveals a novel relationship between NOC1 and MYC transcription factor, known for its crucial role in controlling ribosomal biogenesis, cell growth, and proliferation. Here, we demonstrate that NOC1 functions as a direct target of MYC, as it is transcriptionally induced through a functional MYC-binding E-box sequence in the NOC1 promoter region. Furthermore, protein interactome analysis reveals that NOC1-complex includes the nucleolar proteins NOC2 and NOC3 and other nucleolar components such as Nucleostemin1 Ns1 transporters of ribosomal subunits and components involved in rRNA processing and maturation. In response to MYC, NOC1 expression and localization within the nucleolus significantly increase, suggesting a direct functional link between MYC activity and NOC1 function. Notably, NOC1 over-expression leads to the formation of large nuclear granules and enlarged nucleoli, which co-localize with nucleolar fibrillarin and Ns1. Additionally, we demonstrate that NOC1 expression is necessary for Ns1 nucleolar localization, suggesting a role for NOC1 in maintaining nucleolar structure. Finally, the co-expression of NOC1 and MYC enhances nucleolus size and maintains their co-localization, outlining another aspect of the cooperation between NOC1 and MYC in nucleolar dynamics. This study also reveals an enrichment with NOC1 with few proteins involved in RNA processing, modification, and splicing. Moreover, proteins such as Ythdc1, Flacc, and splenito are known to mediate N6-methyladenosine (m6A) methylation of mRNAs in nuclear export, revealing NOC1's potential involvement in coordinating RNA splicing and nuclear mRNA export. In summary, we uncovered novel roles for NOC1 in nucleolar homeostasis and established its direct connection with MYC in the network governing nucleolar structure and function. These findings also highlight NOC1's interaction with proteins relevant to specific RNA functions, suggesting a broader role in addition to its control of nucleolar homeostasis and providing new insight that can be further investigated.

Distinct dynamics of the nucleolus in response to nutrient availability and during development in the rice blast fungus.

The nucleolus is a dynamic subnuclear structure that is involved in many fundamental processes of the nucleus. In higher eukaryotic cells, the size and shape of nucleoli correlate with nucleolar activities. For fungi, knowledge of the nucleolus and its functions is primarily gleaned from budding yeast. Whether such correlation is conserved and how nucleolar functions are regulated in filamentous fungi including important human and crop pathogens are largely unknown. Our observations reveal that the dynamics of nucleolus in a model plant pathogenic fungus, Magnaporthe oryzae, is distinct from those of animal and yeast nucleoli under low nutrient availability and during pathogenic development. Our data not only provide new insight into the nucleoli in filamentous fungi but also highlight the need for investigating how nucleolar dynamics is regulated in comparison to other eukaryotes.

The stability of NPM1 oligomers regulated by acidic disordered regions controls the quality of liquid droplets.

The nucleolus is a membrane-less nuclear body that typically forms through the process of liquid-liquid phase separation (LLPS) involving its components. NPM1 drives LLPS within the nucleolus and its oligomer formation and inter-oligomer interactions play a cooperative role in inducing LLPS. However, the molecular mechanism underlaying the regulation of liquid droplet quality formed by NPM1 remains poorly understood. In this study, we demonstrate that the N-terminal and central acidic residues within the intrinsically disordered regions (IDR) of NPM1 contribute to attenuating oligomer stability, although differences in the oligomer stability were observed only under stringent conditions. Furthermore, the impact of the IDRs is augmented by an increase in net negative charges resulting from phosphorylation within the IDRs. Significantly, we observed an increase in fluidity of liquid droplets formed by NPM1 with decreased oligomer stability. These results indicate that the difference in oligomer stability only observed biochemically under stringent conditions has a significant impact on liquid droplet quality formed by NPM1. Our findings provide new mechanistic insights into the regulation of nucleolar dynamics during the cell cycle.

Exportin 1 modulates life span by regulating nucleolar dynamics via the autophagy protein LGG-1/GABARAP.

Altered nucleolar and ribosomal dynamics are key hallmarks of aging, but their regulation remains unclear. Building on the knowledge that the conserved nuclear export receptor Exportin 1 (XPO-1/XPO1) modulates proteostasis and life span, we systematically analyzed the impact of nuclear export on protein metabolism. Using transcriptomic and subcellular proteomic analyses in nematodes, we demonstrate that XPO-1 modulates the nucleocytoplasmic distribution of key proteins involved in nucleolar dynamics and ribosome function, including fibrillarin (FIB-1/FBL) and RPL-11 (RPL11). Silencing xpo-1 led to marked reduction in global translation, which was accompanied by decreased nucleolar size and lower fibrillarin levels. A targeted screen of known proteostatic mediators revealed that the autophagy protein LGG-1/GABARAP modulates nucleolar size by regulating RPL-11 levels, linking specific protein degradation to ribosome metabolism. Together, our study reveals that nucleolar size and life span are regulated by LGG-1/GABARAP via ribosome protein surveillance.

Sorting nexin Mdm1/SNX14 regulates nucleolar dynamics at the NVJ after TORC1 inactivation

The degradation of nucleolar proteins – nucleophagy – is elicited by nutrient starvation or the inactivation of target of rapamycin complex 1 (TORC1) protein kinase in budding yeast. Prior to nucleophagy, nucleolar proteins migrate to the nucleus–vacuole junction (NVJ), where micronucleophagy occurs, whereas rDNA (rRNA gene) repeat regions are condensed and escape towards NVJ-distal sites. This suggests that the NVJ controls nucleolar dynamics from outside of the nucleus after TORC1 inactivation, but its molecular mechanism is unclear. Here, we show that sorting nexin (SNX) Mdm1, an inter-organelle tethering protein at the NVJ, mediates TORC1 inactivation-induced nucleolar dynamics. Furthermore, Mdm1 was required for proper nucleophagic degradation of nucleolar proteins after TORC1 inactivation, where it was dispensable for the induction of nucleophagic flux itself. This indicated that nucleophagy and nucleolar dynamics are independently regulated by TORC1 inactivation. Finally, Mdm1 was critical for survival during nutrient starvation conditions. Mutations of SNX14, a human Mdm1 homolog, cause neurodevelopmental disorders. This study provides a novel insight into relationship between sorting nexin-mediated microautophagy and neurodevelopmental disorders.

The vacuole controls nucleolar dynamics and micronucleophagy via the NVJ

Chromosomes have their own territories and dynamically translocate in response to internal and external cues. However, whether and how territories and the relocation of chromosomes are controlled by other intracellular organelles remains unknown. Upon nutrient starvation and target of rapamycin complex 1 (TORC1) inactivation, micronucleophagy, which preferentially degrades nucleolar proteins, occurs at the nucleus–vacuole junction (NVJ) in budding yeast. Ribosomal DNA (rDNA) is condensed and relocated against the NVJ, whereas nucleolar proteins move towards the NVJ for micronucleophagic degradation, causing dissociation of nucleolar proteins from rDNA. These findings imply that the NVJ is the critical platform in the directional movements of rDNA and nucleolar proteins. Here, we show that cells lacking the NVJ (NVJΔ cells) largely lost rDNA condensation and rDNA–nucleolar protein separation after TORC1 inactivation. The macronucleophagy receptor Atg39, an outer nuclear membrane protein, accumulated at the NVJ and was degraded by micronucleophagy. These suggested that macronucleophagy is also dependent on the presence of the NVJ. However, micronucleophagy, but not macronucleophagy, was abolished in NVJΔ cells. This study clearly demonstrated that vacuoles controls intranuclear events, nucleolar dynamics, from outside of the nucleus via the NVJ under the control of TORC1.

Application of carbon dots in nucleolus imaging to distinguish cancerous cells from normal cells

Fluorescent molecular probes are very critical for detecting the precise location of lesions in fundamental research and clinical applications. Herein, we report a green-emitting carbon dots (m-CDs) with excellent properties including good photostability, high cellular uptake efficiency, low cytotoxicity, and good counterstain compatibility. Digest tests of ribonuclease indicate the significantly higher affinity of m-CDs for nucleolus RNA in both fixed and living cells. Notably, visualizing nucleoli in cells by using m-CDs can accurately achieve its number and morphology information to distinguish cancerous cells from normal cells. In addition, m-CDs can also be used to monitor the nucleolar dynamics during apoptosis of malignant cells induced by doxorubicin (DOX). The m-CDs show great potential as a nucleolus probe, and promising applications in cancerous cells screening and therapeutic efficacy evaluation.

Nucleolar dynamics and interactions with nucleoplasm in living cells.

Liquid-liquid phase separation (LLPS) has been recognized as one of the key cellular organizing principles and was shown to be responsible for formation of membrane-less organelles such as nucleoli. Although nucleoli were found to behave like liquid droplets, many ramifications of LLPS including nucleolar dynamics and interactions with the surrounding liquid remain to be revealed. Here, we study the motion of human nucleoli in vivo, while monitoring the shape of the nucleolus-nucleoplasm interface. We reveal two types of nucleolar pair dynamics: an unexpected correlated motion prior to coalescence and an independent motion otherwise. This surprising kinetics leads to a nucleolar volume distribution, [Formula: see text], unaccounted for by any current theory. Moreover, we find that nucleolus-nucleoplasm interface is maintained by ATP-dependent processes and susceptible to changes in chromatin transcription and packing. Our results extend and enrich the LLPS framework by showing the impact of the surrounding nucleoplasm on nucleoli in living cells.

Nucleolar dynamics and interactions with nucleoplasm in living cells

Liquid-liquid phase separation (LLPS) has been recognized as one of the key cellular organizing principles and was shown to be responsible for formation of membrane-less organelles such as nucleoli. Although nucleoli were found to behave like liquid droplets, many ramifications of LLPS including nucleolar dynamics and interactions with the surrounding liquid remain to be revealed. Here, we study the motion of human nucleoli in vivo, while monitoring the shape of the nucleolus-nucleoplasm interface. We reveal two types of nucleolar pair dynamics: an unexpected correlated motion prior to coalescence and an independent motion otherwise. This surprising kinetics leads to a nucleolar volume distribution, , unaccounted for by any current theory. Moreover, we find that nucleolus-nucleoplasm interface is maintained by ATP-dependent processes and susceptible to changes in chromatin transcription and packing. Our results extend and enrich the LLPS framework by showing the impact of the surrounding nucleoplasm on nucleoli in living cells.

Surface Fluctuations and Coalescence of Nucleolar Droplets in the Human Cell Nucleus

The nucleolus is a membraneless organelle embedded in chromatin solution inside the cell nucleus. It is a site of ribosomal biogenesis, plays a key role in cell cycle progression and stress response, and acts as an indicator in many human diseases and aging. However, the physical nature of the human nucleolus remains an open question. Elucidating nucleolar dynamics, such as their shape fluctuations and fusion, could not only help answer this question, but also provide insight into the material properties of the surrounding nucleoplasm. In this work, we analyze the surface dynamics and fusion kinetics of nucleoli in live human cells[1]. Nucleolar surface fluctuations inform on the nucleolus-nucleoplasm interface, while nucleolar fusion might resolve whether nucleoli aggregate like solid particles or coalesce like liquid droplets. We find that the surface exhibits subtle, but measurable, fluctuations and that the neck connecting two fusing nucleoli grows as r(t)∼t1/2. This is consistent with liquid droplets with low surface tension ∼10−6 Nm−1 coalescing in an outer fluid of higher viscosity ∼103 Pa s, i.e. chromatin solution. We hypothesize that the high viscosity of chromatin solution slows down the nucleolar coalescence kinetics to facilitate transcription inside nucleoli. Interestingly, we find the neck velocity, dr/dt, to be comparable to the velocity of chromatin solution[2]. Surprisingly, nucleolar coalescence occurs in an active fluid, yet can be described by coalescence theory for passive liquid droplets, suggesting that the measured viscosity and surface tension might be effective quantities. Our study presents a noninvasive approach of using natural probes, such as nucleoli, and their dynamics to investigate material properties of the cell and its constituents[1]. 1. Caragine CM et al., Phys. Rev. Lett., In Press, 2018. 2. Zidovska A et al., Proc. Natl. Acad. Sci., 110(39), 15555-60, 2013.

Deep-Red Fluorescent Gold Nanoclusters for Nucleoli Staining: Real-Time Monitoring of the Nucleolar Dynamics in Reverse Transformation of Malignant Cells.

Nucleoli are important subnuclear structures inside cells. We report novel fluorescent gold nanoclusters (K-AuNCs) that are able to stain the nucleoli selectively and make it possible to explore the nucleolar morphology with fluorescence imaging technique. This novel probe is prepared through an easy synthesis method by employing a tripeptide (Lys-Cys-Lys) as the surface ligand. The properties, including deep-red fluorescence emission (680 nm), large Stocks shift, broad excitation band, low cytotoxicity, and good photostability, endow this probe with potential for bioanalytical applications. Because of their small size and their positively charged surface, K-AuNCs are able to accumulate efficiently at the nucleolar regions and provide precise morphological information. K-AuNCs are also used to monitor the nucleolar dynamics along the reverse-transformation process of malignant cells, induced by the agonist of protein A, 8-chloro-cyclic adenosine monophosphate. This gives a novel approach for investigating the working mechanism of antitumor drugs.

Nucleolar protein, Myb-binding protein 1A, specifically binds to nonacetylated p53 and efficiently promotes transcriptional activation

Nucleolar dynamics are important for cellular stress response. We previously demonstrated that nucleolar stress induces nucleolar protein Myb-binding protein 1A (MYBBP1A) translocation from the nucleolus to the nucleoplasm and enhances p53 activity. However, the underlying molecular mechanism is understood to a lesser extent. Here we demonstrate that MYBBP1A interacts with lysine residues in the C-terminal regulatory domain region of p53. MYBBP1A specifically interacts with nonacetylated p53 and induces p53 acetylation. We propose that MYBBP1A dissociates from acetylated p53 because MYBBP1A did not interact with acetylated p53 and because MYBBP1A was not recruited to the p53 target promoter. Therefore, once p53 is acetylated, MYBBP1A dissociates from p53 and interacts with nonacetylated p53, which enables another cycle of p53 activation. Based on our observations, this MYBBP1A–p53 binding property can account for efficient p53-activation by MYBBP1A under nucleolar stress. Our results support the idea that MYBBP1A plays catalytic roles in p53 acetylation and activation.

Differential Effects of High-Temperature Stress on Nuclear Topology and Transcription of Repetitive Noncoding and Coding Rye Sequences

The plant stress response has been extensively characterized at the biochemical and physiological levels. However, knowledge concerning repetitive sequence genome fraction modulation during extreme temperature conditions is scarce. We studied high-temperature effects on subtelomeric repetitive sequences (pSc200) and 45S rDNA in rye seedlings submitted to 40°C during 4 h. Chromatin organization patterns were evaluated through fluorescent in situ hybridization and transcription levels were assessed using quantitative real-time PCR. Additionally, the nucleolar dynamics were evaluated through fibrillarin immunodetection in interphase nuclei. The results obtained clearly demonstrated that the pSc200 sequence organization is not affected by high-temperature stress (HTS) and proved for the first time that this noncoding subtelomeric sequence is stably transcribed. Conversely, it was demonstrated that HTS treatment induces marked rDNA chromatin decondensation along with nucleolar enlargement and a significant increase in ribosomal gene transcription. The role of noncoding and coding repetitive rye sequences in the plant stress response that are suggested by their clearly distinct behaviors is discussed. While the heterochromatic conformation of pSc200 sequences seems to be involved in the stabilization of the interphase chromatin architecture under stress conditions, the dynamic modulation of nucleolar and rDNA topology and transcription suggest their role in plant stress response pathways.