Cytoophidia coupling adipose architecture and metabolism

Filamentation and inhibition of prokaryotic CTP synthase with ligands

Cytidine triphosphate synthase (CTPS) plays a pivotal role in the de novo synthesis of cytidine triphosphate (CTP), a fundamental building block for RNA and DNA that is essential for life. CTPS is capable of directly binding to all four nucleotide triphosphates: adenine triphosphate, uridine triphosphate, CTP, and guanidine triphosphate. Furthermore, CTPS can form cytoophidia in vivo and metabolic filaments in vitro, undergoing regulation at multiple levels. CTPS is considered a potential therapeutic target for combating invasions or infections by viral or prokaryotic pathogens. Utilizing cryo-electron microscopy, we determined the structure of Escherichia coli CTPS (ecCTPS) filament in complex with CTP, nicotinamide adenine dinucleotide (NADH), and the covalent inhibitor 6-diazo-5-oxo- l-norleucine (DON), achieving a resolution of 2.9 Å. We constructed a phylogenetic tree based on differences in filament-forming interfaces and designed a variant to validate our hypothesis, providing an evolutionary perspective on CTPS filament formation. Our computational analysis revealed a solvent-accessible ammonia tunnel upon DON binding. Through comparative structural analysis, we discern a distinct mode of CTP binding of ecCTPS that differs from eukaryotic counterparts. Combining biochemical assays and structural analysis, we determined and validated the synergistic inhibitory effects of CTP with NADH or adenine on CTPS. Our results expand our comprehension of the diverse regulatory aspects of CTPS and lay a foundation for the design of specific inhibitors targeting prokaryotic CTPS.

Dynamic Cytoophidia during Late-Stage Drosophila Oogenesis

CTP synthase (CTPS) catalyzes the final step of de novo synthesis of CTP. CTPS was first discovered to form filamentous structures termed cytoophidia in Drosophila ovarian cells. Subsequent studies have shown that cytoophidia are widely present in cells of three life domains. In the Drosophila ovary model, our previous studies mainly focused on the early and middle stages, with less involvement in the later stages. In this work, we focus on the later stages of female germline cells in Drosophila. We use live-cell imaging to capture the continuous dynamics of cytoophidia in Stages 10-12. We notice the heterogeneity of cytoophidia in the two types of germline cells (nurse cells and oocytes), manifested in significant differences in morphology, distribution, and dynamics. Surprisingly, we also find that neighboring nurse cells in the same egg chamber exhibit multiple dynamic patterns of cytoophidia over time. Although the described dynamics may be influenced by the in vitro incubation conditions, our observation provides an initial understanding of the dynamics of cytoophidia during late-stage Drosophila oogenesis.

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.

Cytoophidia Influence Cell Cycle and Size in Schizosaccharomyces pombe

Cytidine triphosphate synthase (CTPS) forms cytoophidia in all three domains of life. Here we focus on the function of cytoophidia in cell proliferation using Schizosaccharomyces pombe as a model system. We find that converting His359 of CTPS into Ala359 leads to cytoophidium disassembly. By reducing the level of CTPS protein or specific mutation, the loss of cytoophidia prolongs the G2 phase and expands cell size. In addition, the loss-filament mutant of CTPS leads to a decrease in the expression of genes related to G2/M transition and cell growth, including histone chaperone slm9. The overexpression of slm9 alleviates the G2 phase elongation and cell size enlargement induced by CTPS loss-filament mutants. Overall, our results connect cytoophidia with cell cycle and cell size control in Schizosaccharomyces pombe.

Fat body-specific reduction of CTPS alleviates HFD-induced obesity

Obesity induced by high-fat diet (HFD) is a multi-factorial disease including genetic, physiological, behavioral, and environmental components. Drosophila has emerged as an effective metabolic disease model. Cytidine 5'-triphosphate synthase (CTPS) is an important enzyme for the de novo synthesis of CTP, governing the cellular level of CTP and the rate of phospholipid synthesis. CTPS is known to form filamentous structures called cytoophidia, which are found in bacteria, archaea, and eukaryotes. Our study demonstrates that CTPS is crucial in regulating body weight and starvation resistance in Drosophila by functioning in the fat body. HFD-induced obesity leads to increased transcription of CTPS and elongates cytoophidia in larval adipocytes. Depleting CTPS in the fat body prevented HFD-induced obesity, including body weight gain, adipocyte expansion, and lipid accumulation, by inhibiting the PI3K-Akt-SREBP axis. Furthermore, a dominant-negative form of CTPS also prevented adipocyte expansion and downregulated lipogenic genes. These findings not only establish a functional link between CTPS and lipid homeostasis but also highlight the potential role of CTPS manipulation in the treatment of HFD-induced obesity.

STAMP: Spatio-Temporal Association Mapping of Proteins

We describe a tool, Spatio-Temporal Association Mapping of Proteins (STAMP), for identifying protein interactomes via proximity labeling. For a proof-of-principle study, we use cytidine 5'-triphosphate synthase (CTPS) as an example. CTPS, a metabolic enzyme, forms filamentous structures termed cytoophidia in various tissues. We apply STAMP to a variety of developmental stages and tissues in Drosophila including adult ovaries. Using a cell-specific GAL4 driver, we verify that TurboID can biotinylate the bait protein CTPS, making possible the identification of protein-protein interactions (PPIs) in individual cells. Using the wild-type and mutant CTPS as bait proteins, STAMP results in two distinct sets of proximate proteomes. Our results suggest that STAMP is a feasible tool to catch in vivo PPIs in situ at a defined spatiotemporal resolution.

Cytoophidia safeguard binucleation of Drosophila male accessory gland cells

Although most cells are mononuclear, the nucleus can exist in the form of binucleate or even multinucleate to respond to different physiological processes. The male accessory gland of Drosophila is the organ that produces semen, and its main cells are binucleate. Here we observe that CTP synthase (CTPS) forms filamentous cytoophidia in binuclear main cells, primarily located at the cell boundary. In CTPSH355A, a point mutation that destroys the formation of cytoophidia, we find that the nucleation mode of the main cells changes, including mononucleates and vertical distribution of binucleates. Although the overexpression of CTPSH355A can restore the level of CTPS protein, it will neither form cytoophidia nor eliminate the abnormal nucleation pattern. Therefore, our data indicate that there is an unexpected functional link between the formation of cytoophidia and the maintenance of binucleation in Drosophila main cells.

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.

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.