Search Results (153)

Optical density (OD)-based cell growth measurement is commonly used in high-throughput screening (HTS) during drug discovery or when deciphering the pharmaceutical mechanism of action. While resuspending the cells via a mixing step is often assumed to be necessary prior to OD measurement, its essentiality in HTS workflows has not been systematically verified. Here, through the measurement of the growth of several strains of the microbial yeast Schizosaccharomyces pombe cells, we compared the overall growth dynamics between samples that have been mixed and not mixed. Using statistical quantification by a two-tailed paired t-test followed by multiple comparison corrections, we concluded from the comparison of the doubling time of cells growing in the exponential phase that mixing did not significantly affect the biological interpretation compared to unmixed samples. Doubling time quantification between mixed and unmixed samples showed a difference of approximately 10% on average based on the assessment of the growth of eight strains. As such, if the experimental outcome can accommodate this level of variability, incorporating a mixing step before OD determination would not be necessary. These observations support the simplification of HTS processes, improving the cost efficacy and process efficiency of readouts, yet maintaining the accuracy of data acquisition. Full article

Glycerophosphocholine (GPC) and glycerophosphoinositol (GPI) are phospholipid metabolites generated by phospholipase-mediated deacylation. In budding yeast, they enter cells via the Git1 permease; in fission yeast, the homolog is Tgp1. This study investigates why GPC is toxic to asp1-STF mutants, where Tgp1 is upregulated due to loss of Asp1 pyrophosphatase, resulting in elevated inositol pyrophosphate 1,5-IP₈. We show that S. pombe Tgp1 specifically transports GPC, explaining why GPC, but not GPI, impairs growth. Increased GPC uptake slows doubling time but does not reduce viability. Toxicity is relieved by deletion of Gde1, a phosphodiesterase that hydrolyzes GPC to choline and glycerol-3-phosphate. Mutations in either the Gde1 active site or SPX domain also suppress toxicity, and radiolabeling confirms both domains are required for enzymatic activity. GPC is toxic in cells vastly overexpressing Tgp1 even without elevated IP₈, but Gde1 loss does not suppress this effect. Similarly, in S. cerevisiae overexpressing the Candida albicans Git3 transporter, GPC provision causes toxicity independent of Gde1. Loss of Gpc1, the acyltransferase converting GPC to lysophosphatidylcholine, does not alter toxicity in either yeast. These findings highlight a conserved process by which GPC regulates growth and reveal a role for IP₈ in modulating this process. Full article

Long noncoding RNAs (lncRNAs) are transcripts generated by polymerase II, therefore subject to 5′ capping and 3′ polyadenylation, categorized as such when they are at least 200 nt in size and lack coding function. The lncRNAs were initially interpreted as spurious transcription products, but over the last two decades an increasing amount of evidence has accumulated for regulatory functions. They are found in all taxonomic groups, including bacteria, archaea, fungi, animals and plants. In fungi, global analyses anticipate their presence in higher numbers than initially expected considering the simplicity of these organisms. Except for the numerous studies performed in budding and fission yeast, relatively few lncRNAs have been investigated in sufficient detail in the rest of the fungi, but their number has increased steadily in recent years. The lncRNAs can be transcribed from intergenic regions or coincide totally or partially with protein-coding genes, in which case they are most frequently antisense transcripts. Their regulatory functions can be performed by a wide variety of mechanisms, both in cis on neighboring genes and in trans on distant genes or on proteins. Among the most frequent mechanisms are interference on the transcription of neighboring genes and generation of epigenetic modifications in the environment of target genes. Here, we review the most representative cases of global analyses of the presence of lncRNAs in fungal transcriptomes and describe the lncRNAs that have received more detailed attention. Full article

Mitochondria possess their own genome, which encodes subunits of the electron transport chain, rendering mitochondrial protein translation essential for cellular energy metabolism. Mitochondrial dysfunction affects nuclear transcription through the retrograde response. We applied RNA-seq to investigate whether and how the inhibition of mitochondrial translation by chloramphenicol (CAP) affects transcriptome regulation in proliferating or stationary-phase cells of Schizosaccharomyces pombe growing in fermentative or respiratory media. Stationary-phase cells in glucose medium exhibited the strongest transcriptome response to CAP, characterized by expression signatures similar to those observed under other stresses, including the retrograde response. The induced genes were also significantly enriched in cytoplasmic carbon metabolism pathways, reflecting a transcriptional reprogramming from respiration to fermentation. The transcription factors Scr1 and Rst2, regulators of carbon catabolite repression (CCR), controlled a common set of carbon metabolism genes in CAP-treated stationary-phase cells, and they showed opposing effects on the lifespan of these cells. Rst2 was required for the induction of carbon metabolism genes and maintained nuclear localization in CAP-treated stationary-phase cells. A systematic genetic interaction screen revealed functional relationships of Rst2 with processes related to stress and starvation responses. These findings uncover a complex transcriptional program in stationary-phase cells that adapt to inhibited mitochondrial translation, including stress- and retrograde-like responses, contributions of the CCR factors Scr1 and Rst2, and adjustment of carbon metabolism to deal with mitochondrial dysfunction. Full article

Chromosome transmission fidelity is vital for organism fitness. Yet, extrinsic and intrinsic changes can affect this process, leading to aneuploidy, the loss/gain of chromosomes, which is a hallmark of cancer. Here, using a haploid fission yeast Schizosaccharomyces pombe strain with a segmental aneuploidy, we assayed genome stability under different temperatures and altered gene dosage. We find that S. pombe genome stability is temperature-dependent and is unexpectedly modulated by intracellular levels of inorganic polyphosphate polymers (polyP). The vtc4⁺ gene, encoding a subunit of the polyP-generating VTC complex, is present twice due to the segmental aneuploidy resulting in a gene-dosage-coupled increase in polyP. Using strains with different amounts of polyP, we find a direct negative correlation between polyP and chromosome segregation fidelity. PolyP modulates the function of the conserved CCAN kinetochore subcomplex, as the abnormal growth phenotype caused by the mutant CCAN protein Fta2-291 was rescued in the absence of polyP, while extra polyP had the opposite effect. Importantly, this appears to occur in part by modulation of the nucleolin Gar2. Gar2 is the functional homolog of the Saccharomyces cerevisiae Nsr1 protein, whose function is modulated by posttranslational polyP-mediated polyphosphorylation. Thus, polyP modulates genome stability, linking cellular metabolism to chromosome transmission fidelity. Full article

Nucleoside analogues are used as drugs and as labels in laboratory-based research. However, the effect of different nucleoside analogue mechanism(s) on cell sensitivity or mutagenesis is unclear. This is particularly important in cancer treatments where checkpoint proteins and DNA damage factors are often mutated. We tested six nucleoside analogues in fission yeast, Schizosaccharomyces pombe. We found that the mutations in the DNA replication checkpoint cause unique sensitivity profiles towards chemotherapeutic nucleoside analogues (gemcitabine, 5-fluorouracil, cytarabine) and the non-clinical analogue bromodeoxyuridine. Antiretroviral compounds, zidovudine and lamivudine, did not alter cell growth. We compared half-maximal inhibitory concentration (IC50) doses between checkpoint deficient yeast strains, examining culture growth and DNA mis-segregation. Intriguingly, gemcitabine and bromodeoxyuridine doses above the IC50 promoted better growth. Above each compound’s IC50 dose we saw that cells were insensitive to nucleoside analogue re-exposure, particularly in DNA replication checkpoint mutants (cds1∆, rad3∆). Thus, pairing nucleoside analogue use with personal genomics may inform drug choice, dose, and schedule. Finally, these data indicate that resistance may be predictable, informing clinical strategy. Full article

Dormancy is a physiological state that enables cells to survive under adverse conditions by halting their proliferation while retaining the capacity to resume growth when conditions become favorable. This remarkable transition between dormant and proliferative states occurs across a wide range of species, including bacteria, fungi, plants, and tardigrades. Among these organisms, yeast cells have emerged as powerful model systems for elucidating the molecular and biophysical principles governing dormancy and dormancy breaking. In this review, we provide a comprehensive summary of current knowledge on the molecular mechanisms underlying cellular dormancy, with particular focus on the two major model yeasts: Saccharomyces cerevisiae and Schizosaccharomyces pombe. Recent advances in multifaceted approaches—such as single-cell RNA-seq, proteomic analysis, and live-cell imaging—have revealed dynamic changes in gene expression, proteome composition, and viability. Furthermore, insights into the biophysical properties of the cytoplasm have offered new understanding of dormant cell regulation through changes in cytoplasmic fluidity. These properties contribute to both the remarkable stability of dormant cells and their capacity to exit dormancy upon environmental cues, deepening our understanding of fundamental cellular survival strategies across diverse species. Full article

Translation initiation in mitochondria involves unique mechanisms distinct from those in the cytosol or in bacteria. The Schizosaccharomyces pombe mitochondrial translation initiation factor 2 (Mti2) is the ortholog of human MTIF2, which plays a vital role in synthesizing proteins in mitochondria. Here, we investigate the insertion domain of Mti2, which stabilizes its interaction with the ribosome and is crucial for efficient translation initiation. Our results show that the insertion domain is critical for the proper folding and function of Mti2. The absence of the insertion domain disrupts cell growth and affects the expression of genes encoded by mitochondrial DNA. Additionally, we show that Mti2 physically interacts with the small subunits of mitoribosomes (mtSSU), and deletion of the insertion domain dissociates mitochondrial initiation factors from the mitoribosome, reducing the efficiency of mitochondrial translation. Altogether, these findings highlight the conserved role of the insertion domain in facilitating translation initiation in fission yeast and thus reveal shared principles of mitochondrial translation initiation in both fission yeast and humans. Full article

The role of calcium, an essential secondary messenger, in cell division remains an outstanding question in cell biology despite several significant findings over the past few decades. Among them is the landmark discovery of intracellular calcium waves during cytokinesis, the last stage of cell division, in fish cells. Nevertheless, subsequent studies have been largely unable to determine the underlying molecular mechanism of these cytokinetic transients. At the center of this stalemate stands two challenging questions, how these calcium transients rise and what they do during cytokinesis. Yeast, despite its proven prowess as a model organism to study cell cycle, has not drawn much interest in addressing these questions. However, the recent discovery of cytokinetic calcium spikes in the fission yeast Schizosaccharomyces pombe has provided novel insights into how calcium regulates cytokinesis. In this review, I will primarily focus on our current understanding of the molecular mechanism of cytokinetic calcium transients in yeast cells. First, I will briefly recount the discovery of cytokinetic calcium transients in animal cells. This will be followed by an introduction to the intracellular calcium homeostasis. Next, I will discuss yeast cytokinetic calcium spikes, the ion channel Pkd2 that promotes these spikes, and the potential molecular targets of these spikes. I will also compare the calcium regulation of cytokinesis between yeast and animal cells. I will conclude by presenting a few critical questions in our continued quest to understand how calcium regulates cytokinesis. Full article

Mitochondria are involved in a wide array of critical cellular processes from energy production to cell death. The morphology (size and shape) of mitochondrial compartments is highly responsive to both intracellular and extracellular conditions, making these organelles highly dynamic. Nutrient levels and stressors both inside and outside the cell inform the balance of mitochondrial fission and fusion and the recycling of mitochondrial components known as mitophagy. The study of mitochondrial morphology and its implications in human disease and microbial engineering have gained significant attention over the past decade. The yeast Saccharomyces cerevisiae offers a valuable model system for studying mitochondria due to its ability to survive without respiring, its genetic tractability, and the high degree of mitochondrial similarity across eukaryotic species. Here, we review how the interplay between mitochondrial fission, fusion, biogenesis, and mitophagy regulates the dynamic nature of mitochondrial networks in both yeast and mammalian systems with an emphasis on yeast as a model organism. Additionally, we examine the crucial role of inter-organelle interactions, particularly between mitochondria and the endoplasmic reticulum, in regulating mitochondrial dynamics. The dysregulation of any of these processes gives rise to abnormal mitochondrial morphologies, which serve as the distinguishing features of numerous diseases, including Parkinson’s disease, Alzheimer’s disease, and cancer. Notably, yeast models have contributed to revealing the underlying mechanisms driving these human disease states. In addition to furthering our understanding of pathologic processes, aberrant yeast mitochondrial morphologies are of increasing interest to the seemingly distant field of metabolic engineering, following the discovery that compartmentalization of certain biosynthetic pathways within mitochondria can significantly improve chemical production. In this review, we examine the utility of yeast as a model organism to study mitochondrial morphology in both healthy and pathologic states, explore the nascent field of mitochondrial morphology engineering, and discuss the methods available for the quantification and classification of these key mitochondrial morphologies. Full article

(1) Background: Quiescent cells are those that have stopped dividing and show strongly reduced levels of gene expression during dormancy. In response to appropriate signals, the cells can wake up and start growing again. Many histone modifications are regulated in quiescence, but their exact functions remain to be determined. (2) Methods: Here, we map the different histone modifications, H3K4me3, H3K9ac, H3K9me2, and H3K9me3, and the histone variant H2A.Z, comparing vegetative and quiescent fission yeast (S. pombe) cells. We also map histone H3 as a control and RNA polymerase II (phosphorylated at S2 and S5) to enable comparisons of their occupancies within genes. We use ChIP-seq methodology and several different bioinformatics tools. (3) Results: The histone modification mapping data show that H3K4me3 changes stand out as being the most significant. Changes in occupancy of histone variant H2A.Z were also significant, consistent with earlier studies. Regarding gene expression changes in quiescence, we found that changes in mRNA levels were associated with changes in occupancy of RNA polymerase II (S2 and S5). Analysis of quiescence genes showed that increased H3K4me3 levels and RNA polymerase II occupancy were super-significant in a small set of core quiescence genes that are continuously upregulated during dormancy. We demonstrate that several of these genes were require Set1C/COMPASS activity for their strong induction during quiescence. (4) Conclusions: Our results imply that regulation of gene expression in quiescent cells involves epigenome changes with a key role for H3K4me3 in regulation of RNA polymerase II activity, and that different gene activation mechanisms control early and core quiescence genes. Thus, our data give further insights into important epigenome changes in quiescence using fission yeast as an experimental model. Full article

The de novo synthesis of cytidine 5′-triphosphate (CTP) is catalyzed by the enzyme CTP synthase (CTPS), which is known to form cytoophidia across all three domains of life. In this study, we use the budding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe as model organisms to compare cytoophidium assembly under external environmental and intracellular CTPS alterations. We observe that under low and high temperature conditions, cytoophidia in fission yeast gradually disassemble, while cytoophidia in budding yeast remain unaffected. The effect of pH changes on cytoophidia maintenance in the two yeast species is different. When cultured in the yeast-saturated cultured medium, cytoophidia in fission yeast disassemble, while cytoophidia in budding yeast gradually form. Overexpression of CTPS results in the presence and maintenance of cytoophidia in both yeast species from the log phase to the stationary phase. In summary, our results demonstrate differential cytoophidium assembly between Saccharomyces cerevisiae and Schizosaccharomyces pombe, the two most studied yeast species. Full article

We investigated whether the elimination of two major enzymes responsible for triacylglycerol synthesis altered the structure and physical state of organelle membranes under mild heat shock conditions in the fission yeast, Schizosaccharomyces pombe. Our study revealed that key intracellular membrane structures, lipid droplets, vacuoles, the mitochondrial network, and the cortical endoplasmic reticulum were all affected in mutant fission yeast cells under mild heat shock but not under normal growth conditions. We also obtained direct evidence that triacylglycerol-deficient cells were less capable than wild-type cells of adjusting their membrane physical properties during thermal stress. The production of thermoprotective molecules, such as HSP16 and trehalose, was reduced in the mutant strain. These findings suggest that an intact system of triacylglycerol metabolism significantly contributes to membrane protection during heat stress. Full article

Cytokinesis is driven in part by the constriction of a ring of actin filaments, myosin motors and other proteins. In fission yeast, three myosins contribute to cytokinesis including a Myosin-V Myo51. As Myosin-Vs typically carry cargo along actin filaments, the role of Myo51 in cytokinesis remains unclear. The previous work suggests that Myo51 may crosslink actin filaments. We hypothesized that if Myo51 crosslinks actin filaments, cells carrying double deletions of ain1, which encodes the crosslinker alpha-actinin, and myo51 (∆ain1 ∆myo51 cells) will exhibit more severe cytokinesis phenotypes than cells with the single ∆ain1 mutation. Contrary to our expectations, we found that the loss of Myo51 in ∆ain1 cells partially rescued the severity of the node clumping phenotype measured in ∆ain1 cells. Furthermore, we describe a normal process of contractile ring “shedding”, the appearance of fragments of ring material extending away from the contractile ring along the ingressing septum that occurs in the second half of constriction. We measured that ∆ain1 ∆myo51 cells exhibit premature and exaggerated shedding. Our work suggests that Myo51 is not a simple actin filament crosslinker. Instead, a role in effective node motion better recapitulates its function during ring assembly and disassembly. Full article

Recombination hotspot-activating DNA sites (e.g., M26, CCAAT, Oligo-C) and their binding proteins (e.g., Atf1-Pcr1 heterodimer; Php2-Php3-Php5 complex, Rst2, Prdm9) regulate the distribution of Spo11 (Rec12)-initiated meiotic recombination. We sought to create 14 different candidate regulatory DNA sites via bp substitutions in the ade6 gene of Schizosaccharomyces pombe. We used a fission yeast-optimized CRISPR-Cas9 system (SpEDIT) and 196 bp-long dsDNA templates with centrally located bp substitutions designed to ablate the genomic PAM site, create specific 15 bp-long DNA sequences, and introduce a stop codon. After co-transformation with a plasmid that encoded both the guide RNA and Cas9 enzyme, about one-third of colonies had a phenotype diagnostic for DNA sequence changes at ade6. PCR diagnostics and DNA sequencing revealed a diverse collection of alterations at the target locus, including: (A) complete or (B) partial template-directed substitutions; (C) non-homologous end joinings; (D) duplications; (E) bp mutations, and (F) insertions of ectopic DNA. We concluded that SpEDIT can be used successfully to generate a diverse collection of DNA sequence elements within a reporter gene of interest. However, its utility is complicated by low efficiency, incomplete template-directed repair events, and undesired alterations to the target locus. Full article