Nuclear Space Research Articles

Pulsed Nuclear Space Propulsion and International Law: Some Preliminary

Pulsed Nuclear Space Propulsion, researched in the 1950s and 1960s by such eminent physicists as Freeman Dyson, Ted Taylor, Theodore von Karman, and Hans Bethe, involves propelling large spacecraft using compact nuclear explosions from specialized atomic devices. This technology is often known by the name of the Air Force project in which it was developed: Orion. It has long been believed that the 1962 Limited Test Ban Treaty prohibits the use of nuclear pulse space propulsion. After a survey of the Orion project and its results and a review of the applicable law, this Article concludes that language in the 1967 Outer Space Treaty may override the Test Ban agreement to permit non-weapons use of nuclear explosives for propulsion. With a new space race taking place and with important actors such as China not subject to the Test Ban Treaty at all, the subject of pulsed nuclear space propulsion deserves another look.

SSX2 promotes the formation of a novel type of intranuclear lamin bodies.

SSX proteins are normally restricted to spermatogenic cells, but ectopic expression can be observed in many types of human cancer. We recently demonstrated that SSX family members may contribute to tumorigenesis by modifying chromatin structure and, in specific settings, compromise chromatin stability. Here, we used normal and tumorigenic breast epithelial cell line models to further study the effect of ectopic expression of SSX2 on nuclear organization. We show that SSX2 induces the formation of a novel type of nucleoplasmic lamin bodies. Ectopic expression of SSX2 in various breast epithelial cell lines led to the formation of a previously undescribed type of intranuclear bodies containing both A and B type lamins but no other components of the nuclear lamina. SSX2-expressing cells contained a highly variable number of lamin bodies distributed throughout the nuclear space. SSX2-mediated establishment of intranuclear lamin bodies could not be linked to previous molecular interactions of SSX proteins, including polycomb proteins and the Mediator complex, but was, however, dependent on S-phase progression. These results reveal a novel interaction between SSX2 and lamins in the nucleoplasmic space. They further suggest that SSX2 promotes the formation of chromatin neighborhoods supporting the organization of lamins into nuclear bodies. We speculate that this may have implications for the organization and functional regulation of chromatin in cancer cells. Our study contributes to the further understanding of the biology of SSX proteins in tumorigenesis.

БЕЗПЕКОВА СТРАТЕГІЯ ПРЕЗИДЕНТА ДОНАЛЬДА ТРАМПА

D. Trump's republican administration has substantially modified US strategic estimation of security challenges and threats, facing the country. The "National Security Strategy – 2017" became a fundamental basis of the security policy. The authors of the "Strategy…" believed Russia and China to be the main security policy problems, threatening the world status of the U.S.A. and a challenge for it's interests. The answer to the challenges should include deployment of the ABM system, capable of neutralizing threats, created by N.Korea and Iran. Opposing China and Russia, called "revisionist states", seeking to change the international status-quo, requires building up and modernizing arms and Armed Forces, in particular, security predominance in nuclear forces, space and cyber-space. An active role was designed for diplomacy and reconnaissance community, involving an increase of their efficiency. On the regional level, priorities included Indo-Pacific region, where the United States had to contain Chinese expansion, and Europe, where Washington intended to counter Russian subversive activity and aggression and to support NATO's defense efforts. Nuclear Posture Review (2018) was one of the key foreign policy strategic documents for the administration of 45th US President Donald Trump. In the context of increasing political and economic confrontation with the People's Republic of China and the aggravation of relations with Iran and North Korea, which were caused by the nuclear component itself, this strategy returned to the methods of confrontation and the nuclear deterrence of the Cold War era. It emphasized the complementarity of the power potential of the armed forces and the diplomatic levers of the international struggle. In the period of new aggravation in the international system caused by the full-scale invasion of the Russian Federation into Ukraine, these very components of the doctrine can become prognostically effective for the current and future American administrations. This article is designed to analyze the key aspects of the National Security Strategy-2017 and the 2018 Nuclear Posture Review that relate to foreign policy and highlight the special aspects and tools that are still relevant for application by the current administration of Joseph Biden in the crisis of the international system.

Plant In Situ Hi-C Experimental Protocol and Bioinformatic Analysis.

Hi-C enables the characterization of the 0conformation of the genome in the three-dimensional nuclear space. This technique has revolutionized our ability to detect interactions between linearly distant genomic sites on a genome-wide scale. Here, we detail a protocol to carry out in situ Hi-C in plants and describe a straightforward bioinformatics pipeline for the analysis of such data, in particular for comparing samples from different organs or conditions.

Acupuncture regulates PI3K/Akt/mTOR signaling and up-regulates cell autophagy to protect sy-novial tissue of adjuvant arthritis rats

To observe the effect of acupuncture of "Yinlingquan"(SP9) and "Sanyinjiao"(SP6) on expression of phosphatidylinositol-3 kinase/protein kinase B/mammalian target protein of rapamycin (PI3K/Akt/mTOR) signaling in adjuvant arthritis (AA) rats, so as to explore its mechanism underlying improvement of AA. Forty-eight male Wistar rats were randomly divided into normal control, AA model, acupuncture and medication (tripterygium wilfordii) groups, with 12 rats in each group. The AA model was established by putting the rats in a windy, cold and wet environment for 12 h, once every day for 21 days and injection of Freund's complete adjuvant (CFA) into the sole of the right hindlimb on the 21st day. Manual acupuncture stimulation was applied at SP9 and SP6 for 30 min/time, once a day for 21 days. Rats of the medication group received gavage of tripterygium wilfordii tablets solution (8 mg/kg), once a day for 21 days, and those of the normal control group and model group received gavage of the same amount of normal saline, once a day for 21 days. The degree of joint swelling and arthritis index (AI) were detected 1 day before modeling, 3 days after modeling, and 21 days after the treatment. Twenty-four hours after the last treatment, the contents of serum cytokines interleukin (IL)-17, IL-6 and tumor necrosis factor (TNF)-α were detected by enzyme-linked immunosorbent assay (ELISA); and changes of synovial ultrastructure were observed under electron microscope. Western blot was used to detect the expression levels of PI3K, Akt, phosphorylated protein kinase B (p-Akt), phosphorylated mammalian rapamycin target protein (p-mTOR), mTOR, microtubule associated protein 1 light chain 3B (LC3-Ⅱ) and mammalian atg6 homologous protein (Beclin-1) in the synovial membrane tissue. Compared with the normal control group, the joint swel-ling degree and AI, contents of serum TNF-α, IL-6 and IL-17, and the expression levels of PI3K, Akt, p-Akt, mTOR and p-mTOR in the synovium were increased in the model group (P<0.05), while the expression levels of LC3-Ⅱ and Beclin-1 proteins in the synovium were significantly decreased (P<0.05). Compared with the model group, the joint swelling degree and AI, contents of serum TNF-α, IL-6 and IL-17, and the expression levels of PI3K, Akt, p-Akt, mTOR and p-mTOR were significantly decreased in the acupuncture and medication groups (P<0.05), while the expresion levels of LC3-Ⅱ and Beclin-1 proteins were significantly increased （P<0.05）. Comparison between the two treatment groups showed that the therapeutic effects of acupuncture were obviously weaker than those of medication in down-regulating TNF-α and IL-6, Akt, p-Akt and mTOR levels (P<0.05) and in up-regulating Beclin-1 expression (P<0.05). Outcomes of electron microscope displayed widened nuclear membrane space, some fractured mitochondrial cristae with vacuoles, expanded rough endoplasmic reticulum, reduction of autophagosomes in the cytoplasm and ruptured synovial cell membrane in the model group, and increase of autophagosomes, deformed organelles in the acupuncture and medication groups. Acupuncture can relieve the inflammatory reactions and joint synovial injury of the affected joint in AA rats which may be associated with its effects in inhibiting PI3K/Akt/mTOR signaling and increasing the auto-phagy level of synovial cells.

Circulating tRNA-Derived Small RNAs as Novel Radiation Biomarkers of Heavy Ion, Proton and X-ray Exposure.

The effective and minimally invasive radiation biomarkers are valuable for exposure scenarios in nuclear accidents or space missions. Recent studies have opened the new sight of circulating small non-coding RNA (sncRNA) as radiation biomarkers. The tRNA-derived small RNA (tsRNA) is a new class of sncRNA. It is more abundant than other kinds of sncRNAs in extracellular vesicles or blood, presenting great potential as promising biomarkers. However, the circulating tsRNAs in response to ionizing radiation have not been reported. In this research, Kunming mice were total-body exposed to 0.05–2 Gy of carbon ions, protons, or X-rays, and the RNA sequencing was performed to profile the expression of sncRNAs in serum. After conditional screening and validation, we firstly identified 5 tsRNAs including 4 tRNA-related fragments (tRFs) and 1 tRNA half (tiRNA) which showed a significant level decrease after exposure to three kinds of radiations. Moreover, the radiation responses of these 5 serum tsRNAs were reproduced in other mouse strains, and the sequences of them could be detected in serum of humans. Furthermore, we developed multi-factor models based on tsRNA biomarkers to indicate the degree of radiation exposure with high sensitivity and specificity. These findings suggest that the circulating tsRNAs can serve as new minimally invasive biomarkers and can make a triage or dose assessment from blood sample collection within 4 h in exposure scenarios.

Exceptional uranium(VI)-nitride triple bond covalency from 15N nuclear magnetic resonance spectroscopy and quantum chemical analysis

Determining the nature and extent of covalency of early actinide chemical bonding is a fundamentally important challenge. Recently, X-ray absorption, electron paramagnetic, and nuclear magnetic resonance spectroscopic studies have probed actinide-ligand covalency, largely confirming the paradigm of early actinide bonding varying from ionic to polarised-covalent, with this range sitting on the continuum between ionic lanthanide and more covalent d transition metal analogues. Here, we report measurement of the covalency of a terminal uranium(VI)-nitride by 15N nuclear magnetic resonance spectroscopy, and find an exceptional nitride chemical shift and chemical shift anisotropy. This redefines the 15N nuclear magnetic resonance spectroscopy parameter space, and experimentally confirms a prior computational prediction that the uranium(VI)-nitride triple bond is not only highly covalent, but, more so than d transition metal analogues. These results enable construction of general, predictive metal-ligand 15N chemical shift-bond order correlations, and reframe our understanding of actinide chemical bonding to guide future studies.

Finite-time thermodynamics and exergy analysis of a Stirling engine for space power generation

In recent years, the interest of space agencies and private companies in space exploration has increased, mainly in deep space missions. This type of mission poses great challenges due to the high energy level demanded from the power systems, requiring a more efficient and compact energy conversion system. Thus, this work carried out a finite-time thermodynamic model and exergy analysis of a Stirling cycle for nuclear space power generation. The thermodynamic model was coupled to a simple dynamic Stirling engine model and takes into account several aspects such as the thermal losses between the hot and cold side of the Stirling cycle, finite-time regeneration, temperature drop along heat pipes, and variable compression ratio. The system performance and component irreversibilities were evaluated by varying the nuclear core temperature and the cold side temperature of the cycle. Then, the figure of merit mass per power output (kg.kW-1) of the energy conversion system was computed, enabling the model to find temperature conditions for a system that aligns high efficiency and compactness. The results showed that the component with the greatest irreversibility is the reactor core with a value of 496.14 kJ, representing 68.18% of the total irreversibility. The exergy analysis showed that only 5.15% of the total exergy is used for power generation and 24.33% is rejected to space. Moreover, the cold side temperature of 352 K provided the system with the lowest value of mass per power output (87.69 kg.kW-1).

Chromatin Organization and Function in Drosophila.

Eukaryotic genomes are packaged into high-order chromatin structures organized in discrete territories inside the cell nucleus, which is surrounded by the nuclear envelope acting as a barrier. This chromatin organization is complex and dynamic and, thus, determining the spatial and temporal distribution and folding of chromosomes within the nucleus is critical for understanding the role of chromatin topology in genome function. Primarily focusing on the regulation of gene expression, we review here how the genome of Drosophila melanogaster is organized into the cell nucleus, from small scale histone–DNA interactions to chromosome and lamina interactions in the nuclear space.

Discrete cis-acting element regulates developmentally timed gene-lamina relocation and neural progenitor competence invivo.

SUMMARYThe nuclear lamina is typically associated with transcriptional silencing, and peripheral relocation of genes highly correlates with repression. However, the DNA sequences and proteins regulating gene-lamina interactions are largely unknown. Exploiting the developmentally timed hunchback gene movement to the lamina in Drosophila neuroblasts, we identified a 250 bp intronic element (IE) both necessary and sufficient for relocation. The IE can target a reporter transgene to the lamina and silence it. Endogenously, however, hunchback is already repressed prior to relocation. Instead, IE-mediated relocation confers a heritably silenced gene state refractory to activation in descendent neurons, which terminates neuroblast competence to specify early-born identity. Surprisingly, we found that the Polycomb group chromatin factors bind the IE and are required for lamina relocation, revealing a nuclear architectural role distinct from their well-known function in transcriptional repression. Together, our results uncover in vivo mechanisms underlying neuroblast competence and lamina association in heritable gene silencing.

Prepare or Resist? Cold War Civil Defence and Imaginaries of Nuclear War in Britain and Denmark in the 1980s

The article explores how the global Cold War conflict was made sense of and situated in local political, cultural and physical landscapes and communities during the 1980s in Britain and Denmark. Using civil defence as a prism, the article employs a comparative approach to explore variations within and between countries of how local authorities prepared or resisted the prospect of nuclear war. The article finds that two main imaginaries emerged that shaped shared understandings of society before, during and after the imagined future war: one emphasized the possibility of nuclear survival and even welfare, the other urged resistance and renounced the futility of civil defence preparations. The article argues that local actors used these imaginaries to empower themselves, to define how nuclear space was imagined and lived and to construct desirable (and undesirable) visions of the future. The imaginaries were multiscalar and interacted with developments at global and national levels, and the article sheds light on this three-way dynamic of understanding and articulating the nuclear age.

Circadian rhythm shows potential for mRNA efficiency and self-organized division of labor in multinucleate cells.

Multinucleate cells occur in every biosphere and across the kingdoms of life, including in the human body as muscle cells and bone-forming cells. Data from filamentous fungi suggest that, even when bathed in a common cytoplasm, nuclei are capable of autonomous behaviors, including division. How does this potential for autonomy affect the organization of cellular processes between nuclei? Here we analyze a simplified model of circadian rhythm, a form of cellular oscillator, in a mathematical model of the filamentous fungus Neurospora crassa. Our results highlight a potential role played by mRNA-protein phase separation to keep mRNAs close to the nuclei from which they originate, while allowing proteins to diffuse freely between nuclei. Our modeling shows that syncytism allows for extreme mRNA efficiency-we demonstrate assembly of a robust oscillator with a transcription rate a thousand-fold less than in comparable uninucleate cells. We also show self-organized division of the labor of mRNA production, with one nucleus in a two-nucleus syncytium producing at least twice as many mRNAs as the other in 30% of cycles. This division can occur spontaneously, but division of labor can also be controlled by regulating the amount of cytoplasmic volume available to each nucleus. Taken together, our results show the intriguing richness and potential for emergent organization among nuclei in multinucleate cells. They also highlight the role of previously studied mechanisms of cellular organization, including nuclear space control and localization of mRNAs through RNA-protein phase separation, in regulating nuclear coordination.

Induction of a chromatin boundary in vivo upon insertion of a TAD border.

Mammalian genomes are partitioned into sub-megabase to megabase-sized units of preferential interactions called topologically associating domains or TADs, which are likely important for the proper implementation of gene regulatory processes. These domains provide structural scaffolds for distant cis regulatory elements to interact with their target genes within the three-dimensional nuclear space and architectural proteins such as CTCF as well as the cohesin complex participate in the formation of the boundaries between them. However, the importance of the genomic context in providing a given DNA sequence the capacity to act as a boundary element remains to be fully investigated. To address this question, we randomly relocated a topological boundary functionally associated with the mouse HoxD gene cluster and show that it can indeed act similarly outside its initial genomic context. In particular, the relocated DNA segment recruited the required architectural proteins and induced a significant depletion of contacts between genomic regions located across the integration site. The host chromatin landscape was re-organized, with the splitting of the TAD wherein the boundary had integrated. These results provide evidence that topological boundaries can function independently of their site of origin, under physiological conditions during mouse development.

Abstract 589: CCR5 upregulation in two subtypes of tumor associated circulating cells predict worse prognosis in metastatic breast cancer

Abstract Background: CCR5 is a motility chemokine receptor implicated in tumor progression, whose activation and endocytosis may identify highly aggressive breast cancer (BC) subtypes likely to spread via the circulatory system. We first studied the activation and endocytosis of CCR5 in response to its ligand CCL5 (RANTES) in the model BC cell line MDA-MB231. We then screened two types of circulating tumor-associated cells (TACs) with known negative clinical outcomes, 1) circulating tumor cells (CTCs) and 2) cancer-associated macrophage-like (CAMLs) cells, to evaluate CCR5 upregulation in relation to disease progression in metastatic breast cancer (mBC). Methods: MB231 cells were used to visualize CCR5 activation within the cell's surface and intracellular space using an anti-CCR5 antibody after stimulation with RANTES. MB231 cells were stained with LAMP-1A to verify co-localization of CCR5 and RANTES to endosomes. Anonymized peripheral blood samples from (n=54) mBC patients were obtained in accordance with local IRB regulations and with informed consent. TACs were isolated using a low-flow CellSieve Microfiltration system and stained for Cytokeratin, CD45, and CCR5. CCR5 expression signal and localization were evaluated on all TACs via fluorescence microscopy. Results: CCR5 in MB231 cells appeared as ~1μm clusters known as “CCR5 pools”, which can be found on the cell's surface, within the cytoplasm, and in the nuclear space. CCR5 pools were upregulated in the presence of RANTES, which appears to relate to endocytosis and nuclear translocation. Within the TACs of mBCs, we found similar patterns of CCR5 pooling with 70% of patients (n=38) having CCR5+ CAMLs and 41% (n=22) having CCR5+ CTCs. It was found that higher numbers of CCR5 pools (≥10pools/cell) were correlated to a 2-fold increase in both CTCs and CAMLs in circulation. In the analysis of outcome data, it was determined that patients having ≥10 CCR5 pools on their CAMLs was a highly significant predictor of worse progression free survival (PFS) and overall survival (OS) (PFS HR=4.8, CI 95% 1.9-11.6, p=0.0015) and (OS HR=3.6, CI 95% 1.3-10.0, p=0.0331). In CTCs ≥10 pools/cell was not a significant predictor for worse PFS and OS. However, ≥5 CCR5 pools/cell significantly predicted for worse PFS but not OS (PFS HR=2.9, CI 95% 1.2-7.4, p=0.0418 and OS HR=3.3, CI 95% 1.1-9.3, p= 0.0539). Conclusion: We observed the activation and endocytosis of CCR5 pools using RANTES in MD-MB231 cell lines, and then demonstrated that this upregulated motility pathway appears to be conserved in migratory cells in mBC patients. Further, this upregulation of CCR5 appears to correlate with worse clinical outcomes, which may provide an explanation for how tumor-associated cells move into circulation and acquire metastatic potential. Citation Format: Ashvathi Raghavakaimal, Massimo Cristofanilli, Cha-Mei Tang, R. K. Alpaugh, Kirby P. Gardener, Saranya Chumsri, Daniel L. Adams. CCR5 upregulation in two subtypes of tumor associated circulating cells predict worse prognosis in metastatic breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 589.

Ultra-Structural Imaging Provides 3D Organization of 46 Chromosomes of a Human Lymphocyte Prophase Nucleus.

Three dimensional (3D) ultra-structural imaging is an important tool for unraveling the organizational structure of individual chromosomes at various stages of the cell cycle. Performing hitherto uninvestigated ultra-structural analysis of the human genome at prophase, we used serial block-face scanning electron microscopy (SBFSEM) to understand chromosomal architectural organization within 3D nuclear space. Acquired images allowed us to segment, reconstruct, and extract quantitative 3D structural information about the prophase nucleus and the preserved, intact individual chromosomes within it. Our data demonstrate that each chromosome can be identified with its homolog and classified into respective cytogenetic groups. Thereby, we present the first 3D karyotype built from the compact axial structure seen on the core of all prophase chromosomes. The chromosomes display parallel-aligned sister chromatids with familiar chromosome morphologies with no crossovers. Furthermore, the spatial positions of all 46 chromosomes revealed a pattern showing a gene density-based correlation and a neighborhood map of individual chromosomes based on their relative spatial positioning. A comprehensive picture of 3D chromosomal organization at the nanometer level in a single human lymphocyte cell is presented.

Brief Review of the Results Regarding the Possible Underlying Mechanisms Driving the Neutrinoless Double Beta Decay

Since the experimental discovery of neutrino oscillations, the search for the neutrinoless double beta (0νββ) decay has intensified greatly, as this particular decay mode, if experimentally discovered, could offer a testing ground for Beyond Standard Model (BSM) theories related to the yet hidden fundamental properties of neutrinos and the possibility of violating of some fundamental symmetries. In this work we make a brief review of the nuclear matrix elements and phase space factors calculations performed mainly by our group. Next, using these calculations and the most recent experimental half-life limits, we revise the constraints on the BSM parameters violating the lepton number corresponding to four mechanisms that could contribute to 0νββ decay. Finally, using the values obtained for the BSM parameters from one of the most sensitive double-beta decay experiments, we provide a comparison with the sensitivities of other experiments.

Cerium Doping Double Perovskite Scintillator for Sensitive X-ray Detection and Imaging.

Scintillators are widely used for nondestructive testing, nuclear medicine imaging, space exploration and security inspection. Recently, lead halide perovskite scintillation crystals have been brought into focus due to their effective atomic number, fast scintillation decay time, strong luminous efficiency, and tunable band gap. However, their application is limited by lead toxicity. Here we report that Ce-doping can increase sensitivity in lead-free double perovskite crystals (Cs2 NaTbCl6 ) for X-ray detection and imaging. The introduction of Ce ions as sensitizer can be used to improve the radioluminescence of the crystals. The light output of Ce : Cs2 NaTbCl6 crystals is about 52153 ph/MeV, which is 25 % higher than that of un-doped crystal. The X-ray sensitivity is significantly enhanced. Based on our scintillation film X-ray detector the detection limit is 30 nGy ⋅ s-1 , which is about 1/183 of the typical medical imaging dose. Our scintillating film has excellent imaging ability with spatial resolution of up to 10 lp/mm. This research shows that Ce : Cs2 NaTbCl6 perovskite crystal scintillators are promising materials for X-ray imaging application.

Transcription Factor Dynamics.

To predict transcription, one needs a mechanistic understanding of how the numerous required transcription factors (TFs) explore the nuclear space to find their target genes, assemble, cooperate, and compete with one another. Advances in fluorescence microscopy have made it possible to visualize real-time TF dynamics in living cells, leading to two intriguing observations: first, most TFs contact chromatin only transiently; and second, TFs can assemble into clusters through their intrinsically disordered regions. These findings suggest that highly dynamic events and spatially structured nuclear microenvironments might play key roles in transcription regulation that are not yet fully understood. The emerging model is that while some promoters directly convert TF-binding events into on/off cycles of transcription, many others apply complex regulatory layers that ultimately lead to diverse phenotypic outputs. Cracking this kinetic code is an ongoing and challenging task that is made possible by combining innovative imaging approaches with biophysical models.

Constraining Dense Matter Physics Using f-Mode Oscillations in Neutron Stars

In this paper, an investigation of the role of nuclear saturation parameters on f-mode oscillations in neutron stars is performed within the Cowling approximation. It is found that the uncertainty in the effective nucleon mass plays a dominant role in controlling the f-mode frequencies. The effect of the uncertainties in saturation parameters on previously-proposed empirical relations of the frequencies with astrophysical observables relevant for asteroseismology are also investigated. These results can serve as an important tool for constraining the nuclear parameter space and understand the behaviour of dense nuclear matter from the future detection of f-modes.

Diploid, triploid, tetraploid - chromatin organization in polyploid watermelon.

The first half of the 20th century was an important time for the scientific discipline of genetics in Japan (Iida, 2010). Hithoshi Kihara (1893–1986) was one of the pioneering researchers who helped to develop the field. He was the first to define the genome as the minimal set of chromosomes that is required for the fitness of a species and he also discovered sex chromosomes in plants. However, the achievement that made him internationally renowned was the development of seedless watermelon (Kihara, 1951). Kihara realized that triploid plants produce seedless fruits, which could be a desirable trait for certain crops. Therefore, he set out to create a triploid watermelon. To do this, he first obtained a tetraploid plant by treating a normal diploid with colchicine, a technique that was discovered shortly before Kiara’s watermelon experiment (Nebel, 1937). Next, he pollinated the tetraploid with pollen from a diploid. This yielded triploid progeny that did not produce seeds. Nowadays, seedless watermelons are still produced similarly. However, there is still a lot that we do not understand. The tetraploid progenitor of triploid watermelon exhibits many phenotypic differences as compared with their diploid counterparts. As yet, it remains enigmatic what causes these differences. Duplication of the genome might lead to rearrangements of the chromatin, because the nucleus needs to accommodate a doubled number of chromosomes. Although the exact effect of chromatin organization on gene regulation is not fully unraveled, it is clear that transcriptional activity is affected by the way the genome is folded (Doğan and Liu, 2018). Hence, altered chromatin organization might (partly) underlie the phenotypic differences in polyploids. In this issue, Marleny Garcia-Lozano and colleagues investigated the effect of genome doubling on chromatin conformation in watermelon. To understand the effect of doubling the number of chromosomes, the authors compared diploid watermelon with an isogenic tetraploid line. Compared to their diploid counterparts, the tetraploid plants had bigger seeds, bigger leaves, and a thicker stem with more and larger trichomes (Figure 1), phenotypes often seen in polyploids. To investigate how the chromatin is organized in diploid and tetraploid plants, the authors employed the Hi-C chromosome conformation capture technique. This technique crosslinks and ligates interacting chromatin fragments, followed by high-throughput sequencing, and is used to identify long-range physical interactions. They found that the interactions between genomic regions were different: in the tetraploid the chromosomes showed a higher number of interactions than in the diploid, especially between regions from different chromosomes. In addition to the chromatin interaction differences, the Hi-C results showed that the chromatin of tetraploid watermelon was organized differently than the chromatin in diploid plants. In eukaryotes, chromatin is divided into two spatially segregated compartments. The chromatin that occupies the interior nuclear space forms the transcriptionally active A compartment, whereas chromatin that resides at the nuclear periphery forms the less active B compartment. In tetraploid watermelon, several chromosomal regions had switched compartments. The authors found that chromatin organization also differed at lower levels of organization. Within the A and B compartments, chromatin is organized in megabase-sized clusters called topologically associated domains (TADs). TADs are demarcated by boundaries that function as insulators. As a result, DNA sequences within a TAD physically interact with each other more frequently than with sequences outside the TAD. The authors identified the boundaries of TADs in diploid and tetraploid watermelon and found that of 346 boundaries, 93 were differential between the two watermelon lines. Besides improved traits such as larger leaves, fruits, and flowers, polyploids can better deal with stressful environments. Therefore, polyploidy has played a key role in plant breeding for many years, and as climate change continues, polyploid crops might become increasingly important. Garcia-Lozano and colleagues found that the presence of a greater number of chromosomes alters the three-dimensional structure of the genome and affects interactions between genomic regions in watermelon. However, it is unclear how the altered chromatin organization affects the phenotype of watermelon after genome duplication. In addition to chromatin organization differences, the authors observed differences in the transcriptome and methylome between diploid and tetraploid watermelon. Seventy years after Kihara’s discovery, there is still a lot to learn about polyploid watermelon.