mTOR-S6K1 pathway mediates cytoophidium assembly

Cytoophidia: a conserved yet promising mode of enzyme regulation in nucleotide metabolism

Nucleotide biosynthesis encompasses both de novo and salvage synthesis pathways, each characterized by significant material and procedural distinctions. Despite these differences, cells with elevated nucleotide demands exhibit a preference for the more intricate de novo synthesis pathway, intricately linked to modes of enzyme regulation. In this study, we primarily scrutinize the biological importance of a conserved yet promising mode of enzyme regulation in nucleotide metabolism-cytoophidia. Cytoophidia, comprising cytidine triphosphate synthase or inosine monophosphate dehydrogenase, is explored across diverse biological models, including yeasts, Drosophila, mice, and human cancer cell lines. Additionally, we delineate potential biomedical applications of cytoophidia. As our understanding of cytoophidia deepens, the roles of enzyme compartmentalization and polymerization in various biochemical processes will unveil, promising profound impacts on both research and the treatment of metabolism-related diseases.

Connecting Hippo Pathway and Cytoophidia in Drosophila Posterior Follicle Cells

CTP synthase (CTPS), the rate-limiting enzyme in the de novo synthesis of CTP, assembles into a filamentous structure termed the cytoophidium. The Hippo pathway regulates cell proliferation and apoptosis. The relationship of the nucleotide metabolism with the Hippo pathway is little known. Here, we study the impact of the Hippo pathway on the cytoophidium in Drosophila melanogaster posterior follicle cells (PFCs). We find that the inactivation of the Hippo pathway correlates with reduced cytoophidium length and number within PFCs. During the overexpression of CTPS, the presence of Hippo mutations also reduces the length of cytoophidia in PFCs. In addition, we observe that knocking down CTPS mitigates hpo (Hippo)-associated over-proliferation. In summary, our results suggest that there is a connection between the Hippo pathway and the nucleotide biosynthesis enzyme CTPS in PFCs.

Differential roles of CTP synthetases CTPS1 and CTPS2 in cell proliferation

The CTP nucleotide is a key precursor of nucleic acids metabolism essential for DNA replication. De novo CTP production relies on CTP synthetases 1 and 2 (CTPS1 and CTPS2) that catalyze the conversion of UTP into CTP. CTP synthetase activity is high in proliferating cells including cancer cells; however, the respective roles of CTPS1 and CTPS2 in cell proliferation are not known. By inactivation of CTPS1 and/or CTPS2 and complementation experiments, we showed that both CTPS1 and CTPS2 are differentially required for cell proliferation. CTPS1 was more efficient in promoting proliferation than CTPS2, in association with a higher intrinsic enzymatic activity that was more resistant to inhibition by 3-deaza-uridine, an UTP analog. The contribution of CTPS2 to cell proliferation was modest when CTPS1 was expressed but essential in absence of CTPS1. Public databases analysis of more than 1,000 inactivated cancer cell lines for CTPS1 or CTPS2 confirmed that cell growth is highly dependent of CTPS1 but less or not of CTPS2. Therefore, our results demonstrate that CTPS1 is the main contributor to cell proliferation.

Retracted: Britannin mediates apoptosis and glycolysis of T-cell lymphoblastic lymphoma cells by AMPK-dependent autophagy

The above article, published online on 19 September 2022 in Wiley Online Library (https://onlinelibrary.wiley.com/doi/abs/10.1002/jbt.23211), has been retracted by agreement between the authors, the journal Editor in Chief, Hari Bhat, and Wiley Periodicals, LLC. The article is being retracted at the authors' request because some of the data underlying this article refer to a different cell line from the one reported in it. As a result, the article's conclusions do not accurately reflect the full data and cannot be considered reliable.

Structural basis of human PRPS2 filaments

BACKGROUND

PRPP synthase (PRPS) transfers the pyrophosphate groups from ATP to ribose-5-phosphate to produce 5-phosphate ribose-1-pyrophosphate (PRPP), a key intermediate in the biosynthesis of several metabolites including nucleotides, dinucleotides and some amino acids. There are three PRPS isoforms encoded in human genome. While human PRPS1 (hPRPS1) and human PRPS2 (hPRPS2) are expressed in most tissues, human PRPS3 (hPRPS3) is exclusively expressed in testis. Although hPRPS1 and hPRPS2 share 95% sequence identity, hPRPS2 has been shown to be less sensitive to allosteric inhibition and specifically upregulated in certain cancers in the translational level. Recent studies demonstrate that PRPS can form a subcellular compartment termed the cytoophidium in multiple organisms across prokaryotes and eukaryotes. Forming filaments and cytoophidia is considered as a distinctive mechanism involving the polymerization of the protein. Previously we solved the filament structures of Escherichia coli PRPS (ecPRPS) using cryo-electron microscopy (cryo-EM) ¹.

RESULTS

Order to investigate the function and molecular mechanism of hPRPS2 polymerization, here we solve the polymer structure of hPRPS2 at 3.08 Å resolution. hPRPS2 hexamers stack into polymers in the conditions with the allosteric/competitive inhibitor ADP. The binding modes of ADP at the canonical allosteric site and at the catalytic active site are clearly determined. A point mutation disrupting the inter-hexamer interaction prevents hPRPS2 polymerization and results in significantly reduced catalytic activity.

CONCLUSION

Findings suggest that the regulation of hPRPS2 polymer is distinct from ecPRPS polymer and provide new insights to the regulation of hPRPS2 with structural basis.

Cytoophidia Maintain the Integrity of Drosophila Follicle Epithelium

CTP synthase (CTPS) forms a filamentous structure termed the cytoophidium in all three domains of life. The female reproductive system of Drosophila is an excellent model for studying the physiological function of cytoophidia. Here, we use CTPS^H355A, a point mutation that destroys the cytoophidium-forming ability of CTPS, to explore the in vivo function of cytoophidia. In CTPS^H355A egg chambers, we observe the ingression and increased heterogeneity of follicle cells. In addition, we find that the cytoophidium-forming ability of CTPS, rather than the protein level, is the cause of the defects observed in CTPS^H355A mutants. To sum up, our data indicate that cytoophidia play an important role in maintaining the integrity of follicle epithelium.

Ubiquitination regulates cytoophidium assembly in Schizosaccharomyces pombe

CTP synthase (CTPS), a metabolic enzyme responsible for the de novo synthesis of CTP, can form filamentous structures termed cytoophidia, which are evolutionarily conserved from bacteria to humans. Here we used Schizosaccharomyces pombe to study the cytoophidium assembly regulation by ubiquitination. We tested the CTP synthase's capacity to be post-translationally modified by ubiquitin or be affected by the ubiquitination state of the cell and showed that ubiquitination is important for the maintenance of the CTPS filamentous structure in fission yeast. We have identified proteins which are in complex with CTPS, including specific ubiquitination regulators which significantly affect CTPS filamentation, and mapped probable ubiquitination targets on CTPS. Furthermore, we discovered that a cohort of deubiquitinating enzymes is important for the regulation of cytoophidium's filamentous morphology. Our study provides a framework for the analysis of the effects that ubiquitination and deubiquitination have on the formation of cytoophidia.

Super-Resolution Imaging Reveals Dynamic Reticular Cytoophidia

CTP synthase (CTPS) can form filamentous structures termed cytoophidia in cells in all three domains of life. In order to study the mesoscale structure of cytoophidia, we perform fluorescence recovery after photobleaching (FRAP) and stimulated emission depletion (STED) microscopy in human cells. By using an EGFP dimeric tag as a tool to explore the physical properties of cytoophidia, we find that cytoophidia are dynamic and reticular. The reticular structure of CTPS cytoophidia may provide space for other components, such as IMPDH. In addition, we observe CTPS granules with tentacles.

Cytoophidia coupling adipose architecture and metabolism

Tissue architecture determines its unique physiology and function. How these properties are intertwined has remained unclear. Here we show that the metabolic enzyme CTP synthase (CTPS) form filamentous structures termed cytoophidia along the adipocyte cortex in Drosophila adipose tissue. Loss of cytoophidia, whether due to reduced CTPS expression or a point mutation that specifically abrogates its polymerization ability, causes impaired adipocyte adhesion and defective adipose tissue architecture. Moreover, CTPS influences integrin distribution and dot-like deposition of type IV collagen (Col IV). Col IV-integrin signaling reciprocally regulates the assembly of cytoophidia in adipocytes. Our results demonstrate that a positive feedback signaling loop containing both cytoophidia and integrin adhesion complex couple tissue architecture and metabolism in Drosophila adipose tissue.

Recent advances of the mammalian target of rapamycin signaling in mesenchymal stem cells

Mammalian target of rapamycin (mTOR) is a serine/threonine kinase involved in a variety of cellular functions, such as cell proliferation, metabolism, autophagy, survival and cytoskeletal organization. Furthermore, mTOR is made up of three multisubunit complexes, mTOR complex 1, mTOR complex 2, and putative mTOR complex 3. In recent years, increasing evidence has suggested that mTOR plays important roles in the differentiation and immune responses of mesenchymal stem cells (MSCs). In addition, mTOR is a vital regulator of pivotal cellular and physiological functions, such as cell metabolism, survival and ageing, where it has emerged as a novel therapeutic target for ageing-related diseases. Therefore, the mTOR signaling may develop a large impact on the treatment of ageing-related diseases with MSCs. In this review, we discuss prospects for future research in this field.

Molecular crowding facilitates bundling of IMPDH polymers and cytoophidium formation

The cytoophidium is a unique type of membraneless compartment comprising of filamentous protein polymers. Inosine monophosphate dehydrogenase (IMPDH) catalyzes the rate-limiting step of de novo GTP biosynthesis and plays critical roles in active cell metabolism. However, the molecular regulation of cytoophidium formation is poorly understood. Here we show that human IMPDH2 polymers bundle up to form cytoophidium-like aggregates in vitro when macromolecular crowders are present. The self-association of IMPDH polymers is suggested to rely on electrostatic interactions. In cells, the increase of molecular crowding with hyperosmotic medium induces cytoophidia, while the decrease of that by the inhibition of RNA synthesis perturbs cytoophidium assembly. In addition to IMPDH, CTPS and PRPS cytoophidium could be also induced by hyperosmolality, suggesting a universal phenomenon of cytoophidium-forming proteins. Finally, our results indicate that the cytoophidium can prolong the half-life of IMPDH, which is proposed to be one of conserved functions of this subcellular compartment.

Filamentation modulates allosteric regulation of PRPS

Phosphoribosyl pyrophosphate (PRPP) is a key intermediate in the biosynthesis of purine and pyrimidine nucleotides, histidine, tryptophan, and cofactors NAD and NADP. Abnormal regulation of PRPP synthase (PRPS) is associated with human disorders, including Arts syndrome, retinal dystrophy, and gouty arthritis. Recent studies have demonstrated that PRPS can form filamentous cytoophidia in eukaryotes. Here, we show that PRPS forms cytoophidia in prokaryotes both in vitro and in vivo. Moreover, we solve two distinct filament structures of E. coli PRPS at near-atomic resolution using Cryo-EM. The formation of the two types of filaments is controlled by the binding of different ligands. One filament type is resistant to allosteric inhibition. The structural comparison reveals conformational changes of a regulatory flexible loop, which may regulate the binding of the allosteric inhibitor and the substrate ATP. A noncanonical allosteric AMP/ADP binding site is identified to stabilize the conformation of the regulatory flexible loop. Our findings not only explore a new mechanism of PRPS regulation with structural basis, but also propose an additional layer of cell metabolism through PRPS filamentation.

CTP synthase does not form cytoophidia in Drosophila interfollicular stalks

CTP synthase (CTPS) catalyzes the final step of de novo synthesis of the nucleotide CTP. In 2010, CTPS has been found to form filamentous structures termed cytoophidia in Drosophila follicle cells and germline cells. Subsequently, cytoophidia have been reported in many species across three domains of life: bacteria, eukaryotes and archaea. Forming cytoophidia appears to be a highly conserved and ancient property of CTPS. To our surprise, here we find that polar cells and stalk cells, two specialized types of cells composing Drosophila interfollicular stalks, do not possess obvious cytoophidia. We show that Myc level is low in these two types of cells. Treatment with a glutamine analog, 6-diazo-5-oxo-l-norleucine (DON), increases cytoophidium assembly in main follicle cells, but not in polar cells or stalk cells. Moreover, overexpressing Myc induces cytoophidium formation in stalk cells. When CTPS is overexpressed, cytoophidia can be observed both in stalk cells and polar cells. Our findings provide an interesting paradigm for the in vivo study of cytoophidium assembly and disassembly among different populations of follicle cells.

Combined Inactivation of CTPS1 and ATR Is Synthetically Lethal to MYC-Overexpressing Cancer Cells

The "undruggable" oncogene MYC supports cancer cell proliferation and survival through parallel induction of multiple anabolic processes. Here we find that inhibiting CTP synthase (CTPS) selectively decreases cell viability and induces DNA replication stress in MYC-overexpressing cells. MYC-driven rRNA synthesis caused the selective DNA replication stress upon CTPS inhibition. Combined inhibition of CTPS and ataxia telangiectasia and Rad3-related protein (ATR) is synthetically lethal in MYC-overexpressing cells, promoting cell death in vitro and decreasing tumor growth in vivo. Unexpectedly, interfering with CTPS1 but not CTPS2 is required to induce replication stress in MYC-deregulated cancer cells and consequent cell death in the presence of an ATR inhibitor. These results highlight a specific and key role of CTPS1 in MYC-driven cancer, suggesting that selectively inhibiting CTPS1 in combination with ATR could be a promising strategy to combat disease progression.

SIGNIFICANCE

Inhibition of CTPS in MYC-overexpressing cells blocks pyrimidine synthesis while maintaining ribosome synthesis activity to create an anabolic imbalance that induces replication stress, providing a new approach to selectively target MYC-driven cancer. See related commentary by Chabanon and Postel-Vinay, p. 969.

CTP synthase: the hissing of the cellular serpent

CTP biosynthesis is carried out by two pathways: salvage and de novo. CTPsyn catalyzes the latter. The study of CTPsyn activity in mammalian cells began in the 1970s, and various fascinating discoveries were made regarding the role of CTPsyn in cancer and development. However, its ability to fit into a cellular serpent-like structure, termed 'cytoophidia,' was only discovered a decade ago by three independent groups of scientists. Although the self-assembly of CTPsyn into a filamentous structure is evolutionarily conserved, the enzyme activity upon this self-assembly varies in different species. CTPsyn is required for cellular development and homeostasis. Changes in the expression of CTPsyn cause developmental changes in Drosophila melanogaster. A high level of CTPsyn activity and formation of cytoophidia are often observed in rapidly proliferating cells such as in stem and cancer cells. Meanwhile, the deficiency of CTPsyn causes severe immunodeficiency leading to immunocompromised diseases caused by bacteria, viruses, and parasites, making CTPsyn an attractive therapeutic target. Here, we provide an overview of the role of CTPsyn in cellular and disease perspectives along with its potential as a drug target.

Drosophila intestinal homeostasis requires CTP synthase

CTP synthase (CTPS) senses all four nucleotides and forms filamentous structures termed cytoophidia in all three domains of life. How CTPS and cytoophidia function in a developmental context, however, remains underexplored. We report that CTPS forms cytoophidia in a subset of cells in the Drosophila midgut. We found that cytoophidia exist in intestinal stem cells (ISC) and enteroblasts in similar proportions. Both refeeding after starvation and feeding with dextran sulfate sodium (DSS) induce ISC proliferation and elongate cytoophidia. Knockdown of CTPS inhibits ISC proliferation. Remarkably, disruption of CTPS cytoophidia inhibits DSS-induced ISC proliferation. Taken together, these data suggest that both the expression level and the filament-form property of CTPS are crucial for intestinal homeostasis in Drosophila.

Functionalized Gadofullerene Ameliorates Impaired Glycolipid Metabolism in Type 2 Diabetic Mice

The soaring global prevalence of diabetes makes it urgent to explore new drugs with high efficacy and safety. Nanomaterial-derived bioactive agents are emerging as one of the most promising candidates for biomedical application. In the present study, we investigated the anti-diabetic effects of a functionalized gadofullerene (GF) using obese db/db and non-obese MKR mouse T2DM models. In both mouse models, the diabetic phenotypes including hyperglycemia, impaired glucose tolerance and insulin sensitivity were ameliorated following 2 or 4 weeks of i.p. administration of GF. GF lowered blood glucose levels in a dose-dependent manner. Importantly, the restored blood glucose levels could persist 10 days after withdrawal of GF treatment. The hepatic AKT/GSK3β/FoxO1 pathway is shown to be the main target of GF for re-balancing gluconeogenesis and glycogen synthesis in vivo and in vitro. In addition, GF treatment significantly reduced weight gain of db/db mice with reduced hepatic fat storage by the inhibition of de novo lipogenesis through mTOR/S6K/SREBP1 pathway. Our data provide compelling evidence to support the promising application of GF for the treatment of T2DM.

Highly effective proximate labeling in Drosophila

The protein-protein interaction (PPI) is a basic strategy for life to operate. The analysis of PPIs in multicellular organisms is very important but extremely challenging because PPIs are particularly dynamic and variable among different development stages, tissues, cells, and even organelles. Therefore, understanding PPI needs a good resolution of time and space. More importantly, understanding in vivo PPI needs to be realized in situ. Proximity-based biotinylation combined with mass spectrometry (MS) has emerged as a powerful approach to study PPI networks and protein subcellular compartmentation. TurboID, the newly engineered promiscuous ligase, has been reported to label proximate proteins effectively in various species. In Drosophila, we systematically apply TurboID-mediated biotinylation in a wide range of developmental stages and tissues, and demonstrate the feasibility of TurboID-mediated labeling system in desired cell types. For a proof-of-principle, we use the TurboID-mediated biotinylation coupled with MS to distinguish CTP synthase with or without the ability to form filamentous cytoophidia, retrieving two distinct sets of proximate proteomes. Therefore, this makes it possible to map PPIs in vivo and in situ at a defined spatiotemporal resolution, and demonstrates a referable resource for cytoophidium proteome in Drosophila.

ASNS disruption shortens CTPS cytoophidia in Saccharomyces cerevisiae

Asparagine synthetase (ASNS) and CTP synthase (CTPS) are two metabolic enzymes that catalyze the biosynthesis of asparagine and CTP, respectively. Both CTPS and ASNS have been identified to form cytoophidia in Saccharomyces cerevisiae. Glutamine is a common substrate for both these enzymes, and they play an important role in glutamine homeostasis. Here, we find that the ASNS cytoophidia are shorter than the CTPS cytoophidia, and that disruption of ASNS shortens the length of CTPS cytoophidia. However, the deletion of CTPS has no effect on the formation and length of ASNS cytoophidia, or on the ASNS protein level. We also find that Asn1 overexpression induces the formation of a multi-dot structure in diauxic phase which suggests that the increased protein level may trigger cytoophidia formation. Collectively, our results reveal a connection between ASNS cytoophidia and CTPS cytoophidia.

CTPS forms the cytoophidium in zebrafish

Cytidine triphosphate synthase (CTPS) catalyzes the rate-limiting step of de novo CTP biosynthesis. An intracellular structure of CTPS, the cytoophidium, has been found in many organisms including prokaryotes and eukaryotes. Formation of the cytoophidium has been suggested to regulate the activity and stability of CTPS and may participate in certain physiological events. Herein, we demonstrate that both CTPS1a and CTPS1b in zebrafish are able to form the cytoophidium in cultured cells. A point mutation, H355A, abrogates cytoophidium assembly of zebrafish CTPS1a and CTPS1b. In addition, we show the presence of CTPS cytoophidia in multiple tissues of larval and adult fish under normal conditions, while treatment with a CTPS inhibitor 6-diazo-5-oxo-l-norleucine (DON) can induce more cytoophidia in some tissues. Our findings reveal that forming the CTPS cytoophidium is a natural phenomenon of zebrafish and provide valuable information for future research on the physiological importance of this intracellular structure in vertebrates.

Freedom of assembly: metabolic enzymes come together

Many different enzymes in intermediate metabolism dynamically assemble filamentous polymers in cells, often in response to changes in physiological conditions. Most of the enzyme filaments known to date have only been observed in cells, but in a handful of cases structural and biochemical studies have revealed the mechanisms and consequences of assembly. In general, enzyme polymerization functions as a mechanism to allosterically tune enzyme kinetics, and it may play a physiological role in integrating metabolic signaling. Here, we highlight some principles of metabolic filaments by focusing on two well-studied examples in nucleotide biosynthesis pathways—inosine-5’-monophosphate (IMP) dehydrogenase and cytosine triphosphate (CTP) synthase.

CTPS and IMPDH form cytoophidia in developmental thymocytes

The cytoophidium, a filamentous structure formed by metabolic enzymes, has emerged as a novel regulatory machinery for certain proteins. The rate-limiting enzymes of de novo CTP and GTP synthesis, cytidine triphosphate synthase (CTPS) and inosine monophosphate dehydrogenase (IMPDH), are the most characterized cytoophidium-forming enzymes in mammalian models. Although the assembly of CTPS cytoophidia has been demonstrated in various organisms including multiple human cancers, a systemic survey for the presence of CTPS cytoophidia in mammalian tissues in normal physiological conditions has not yet been reported. Herein, we examine major organs of adult mouse and observe that CTPS cytoophidia are displayed by a specific thymocyte population ranging between DN3 to early DP stages. Most of these cytoophidium-presenting cells have both CTPS and IMPDH cytoophidia and undergo rapid cell proliferation. In addition, we show that cytoophidium formation is associated with active glycolytic metabolism as the cytoophidium-presenting cells exhibit higher levels of c-Myc, phospho-Akt and PFK. Inhibition of glycolysis with 2DG, however, disrupts most of cytoophidium structures and impairs cell proliferation. Our findings not only indicate that the regulation of CTPS and IMPDH cytoophidia are correlated with the metabolic switch triggered by pre-TCR signaling, but also suggest physiological roles of the cytoophidium in thymocyte development.

Histone transcription regulator Slm9 is required for cytoophidium biogenesis

The cytoophidium, a subcellular structure composed of CTP synthase, can be observed during the division of Schizosaccharomyces pombe. Cytoophidium formation changes periodically with the cell cycle of yeast cells. Here, we find that histone chaperone Slm9 is required for the integrity of cytoophidia in fission yeast. When the slm9 gene is knocked out, we observe that morphological characteristics, the abundance of cytoophidia and the division of the yeast cells are significantly affected. Fragmented cytoophidia occur in slm9 mutant cells, a phenomenon rarely observed in wild-type cells. Our study reveals a potential link between a chromosomal regulatory factor and cytoophidium biogenesis.

Polarised maintenance of cytoophidia in Drosophila follicle epithelia

The metabolic enzyme CTP synthase (CTPS) can form filamentous structures named cytoophidia in numerous types of cells, including follicle cells. However, the regulation of cytoophidium assembly remains elusive. The apicobasal polarity, a defining characteristic of Drosophila follicle epithelium, is established and regulated by a variety of membrane domains. Here we show that CTPS can form cytoophidia in Drosophila epithelial follicle cells. Cytoophidia localise to the basolateral side of follicle cells. If apical polarity regulators are knocked down, cytoophidia become unstable and distribute abnormally. Knockdown of basolateral polarity regulators has no significant effect on cytoophidia, even though the polarity is disturbed. Our results indicate that cytoophidia are maintained via polarised distribution on the basolateral side of Drosophila follicle epithelia, which is primarily achieved through the apical polarity regulators.

A Path toward SARS-CoV-2 Attenuation: Metabolic Pressure on CTP Synthesis Rules the Virus Evolution

In the context of the COVID-19 pandemic, we describe here the singular metabolic background that constrains enveloped RNA viruses to evolve toward likely attenuation in the long term, possibly after a step of increased pathogenicity. Cytidine triphosphate (CTP) is at the crossroad of the processes allowing SARS-CoV-2 to multiply, because CTP is in demand for four essential metabolic steps. It is a building block of the virus genome, it is required for synthesis of the cytosine-based liponucleotide precursors of the viral envelope, it is a critical building block of the host transfer RNAs synthesis and it is required for synthesis of dolichol-phosphate, a precursor of viral protein glycosylation. The CCA 3'-end of all the transfer RNAs required to translate the RNA genome and further transcripts into the proteins used to build active virus copies is not coded in the human genome. It must be synthesized de novo from CTP and ATP. Furthermore, intermediary metabolism is built on compulsory steps of synthesis and salvage of cytosine-based metabolites via uridine triphosphate that keep limiting CTP availability. As a consequence, accidental replication errors tend to replace cytosine by uracil in the genome, unless recombination events allow the sequence to return to its ancestral sequences. We document some of the consequences of this situation in the function of viral proteins. This unique metabolic setup allowed us to highlight and provide a raison d'être to viperin, an enzyme of innate antiviral immunity, which synthesizes 3'-deoxy-3',4'-didehydro-CTP as an extremely efficient antiviral nucleotide.

The atlas of cytoophidia in Drosophila larvae

In 2010, cytidine 5'-triphosphate synthase (CTPS) was reported to form the filamentous or serpentine structure in Drosophila, which we termed the cytoophidium. In the last decade, CTPS filaments/cytoophidia have been found in bacteria, budding yeast, human cells, mice, fission yeast, plants, and archaea, indicating that this mechanism is highly conserved in evolution. In addition to CTPS, other metabolic enzymes have been identified to have the characteristics of forming cytoophidia or similar advanced structures, demonstrating that this is a basic strategy of cells. Nevertheless, our understanding of the physiological function of the cytoophidium remains incomplete and elusive. Here, we took the larva of Drosophila melanogaster as a model to systematically describe the localization and distribution of cytoophidia in different tissues during larval development. We found that the distribution pattern of CTPS cytoophidia is dynamic and heterogenic in larval tissues. Our study provides a road map for further understanding of the function and regulatory mechanism of cytoophidia.

The proline synthesis enzyme P5CS forms cytoophidia in Drosophila

Compartmentation of enzymes via filamentation has arisen as a mechanism for the regulation of metabolism. In 2010, three groups independently reported that CTP synthase (CTPS) can assemble into a filamentous structure termed the cytoophidium. In searching for CTPS-interacting proteins, here we perform a yeast two-hybrid screening of Drosophila proteins and identify a putative CTPS-interacting protein, △¹-pyrroline-5-carboxylate synthase (P5CS). Using the Drosophila follicle cell as the in vivo model, we confirm that P5CS forms cytoophidia, which are associated with CTPS cytoophidia. Overexpression of P5CS increases the length of CTPS cytoophidia. Conversely, filamentation of CTPS affects the morphology of P5CS cytoophidia. Finally, in vitro analyses confirm the filament-forming property of P5CS. Our work links CTPS with P5CS, two enzymes involved in the rate-limiting steps in pyrimidine and proline biosynthesis, respectively.

Distinct effects of thermal treatments after lengthening contraction on mechanical hyperalgesia and exercise-induced physiological changes in rat muscle

Delayed-onset muscle soreness (DOMS) is a common but displeasing event induced by excessive muscle use or unaccustomed exercise and characterized by tenderness and movement-related pain in the exercised muscle. Thermal therapies, either icing or heating applied to muscles immediately after exercise, have been used as therapeutic interventions for DOMS. However, the mechanisms of their analgesic effects, and physiological and metabolic changes in the muscle during thermal therapy, remain unclear. In the present study, we investigated the effects of both thermal treatments on mechanical hyperalgesia of DOMS and physiological and muscle metabolite changes using the rat DOMS model induced by lengthening contraction (LC) to the gastrocnemius muscle. Heating treatment just after LC induced analgesic effects, while rats with icing treatment showed mechanical hyperalgesia similar to that of the LC group. Furthermore, increased physiological responses (e.g., muscle temperature and blood flow) following the LC were significantly kept high only in the rats with heating treatment. In addition, heating treatment increased metabolites involved in the improvement of blood flow and oxidative metabolisms in the exercised muscle. The results indicated that heating treatment just after LC has analgesic effects on DOMS, which might be mediated partly through the improvement of muscle oxidative metabolisms by changes in metabolites and elevated physiological responses.NEW & NOTEWORTHY Physiological effects of thermal therapy in the muscle and its mechanisms of analgesic effects remain unclear. The results indicated that heating, but not icing, treatment just after lengthening contractions induced analgesic effects in the rat muscle. Increases in hemodynamics, muscle temperature, and metabolites such as nicotinamide were more prominent in heating treatment, consistent with improvement of muscle oxidative metabolisms, which might reduce chemical factors to induce mechanical hyperalgesia.

The TOR pathway modulates cytoophidium formation in Schizosaccharomyces pombe

CTP synthase (CTPS) has been demonstrated to form evolutionarily-conserved filamentous structures termed cytoophidia whose exact cellular functions remain unclear, but they may play a role in intracellular compartmentalization. We have previously shown that the mammalian target of rapamycin complex 1 (mTORC1)-S6K1 pathway mediates cytoophidium assembly in mammalian cells. Here, using the fission yeast Schizosaccharomyces pombe as a model of a unicellular eukaryote, we demonstrate that the target of rapamycin (TOR)-signaling pathway regulates cytoophidium formation (from the S. pombe CTPS ortholog Cts1) also in S. pombe Conducting a systematic analysis of all viable single TOR subunit-knockout mutants and of several major downstream effector proteins, we found that Cts1 cytoophidia are significantly shortened and often dissociate when TOR is defective. We also found that the activities of the downstream effector kinases of the TORC1 pathway, Sck1, Sck2, and Psk1 S6, as well as of the S6K/AGC kinase Gad8, the major downstream effector kinase of the TORC2 pathway, are necessary for proper cytoophidium filament formation. Interestingly, we observed that the Crf1 transcriptional corepressor for ribosomal genes is a strong effector of Cts1 filamentation. Our findings connect TOR signaling, a major pathway required for cell growth, with the compartmentalization of the essential nucleotide synthesis enzyme CTPS, and we uncover differences in the regulation of its filamentation among higher multicellular and unicellular eukaryotic systems.