Histone modification and nucleosome assembly play important roles in chromatin-related processes.Histone chaperones form different complexes and coordinate histone transportation and assembly.Various histone chaperone complexes have been identified in different organisms.The ciliate protozoa(ciliates)have various chromatin structures and different nuclear morphology.However,histone chaperone components and functions of different subunits remain unclear in ciliates.Tet-rahymema thermophila contains a transcriptionally active macronucleus(MAC)and a transcriptionally inactive micronu-cleus(MIC)which exhibit multiple replication and various chromatin remodeling progresses during vegetative growth and sexual developmental stages.Here,we found histone chaperone RebL1 not only localized evenly in the transcriptionally active MAC but also dynamically changed in the MIC during vegetative growth and sexual developmental stages.REBL1 knockdown inhibited cellular proliferation.The macronuclear morphology became bigger in growing mutants.The abnormal macronuclear structure also occurred in the starvation stage.Furthermore,micronuclear meiosis was disturbed during sexual development,leading to a failure to generate new gametic nuclei.RebL1 potentially interacted with various factors involved in histone-modifying complexes and chromatin remodeling complexes in different developmental stages.REBL1 knockdown affected expression levels of the genes involved in chromatin organization and transcription.Taken together,RebL1 plays a vital role in maintaining macronuclear structure stability and gametogenesis in T.thermophila.
Huijuan HaoYinjie LianChenhui RenSitong YangMin ZhaoTao BoJing XuWei Wang
Pyraclostrobin(PYR),a widely used fungicide,has negative effects on fish and algae,but its toxicity in protozoa remains unclear.In this study,the effects of PYR on the growth,oxidative stress,and gene expression related to stress and ATP-binding cassette(ABC)transporters in Tetrahymena thermophila were investigated.The result showed that the 96-h IC_(50)of PYR against T.thermophila was 17.2 mg/L.Moreover,PYR inhibited the growth of T.thermophila in concentration-or time-dependent manner.A morphological study revealed that the shape and size of T.thermophila changed,and damage of cell membrane surface was observed by scanning electron microscopy after 96 h of PYR exposure.The activities of superoxide dismutase(SOD)and catalase(CAT)increased throughout the experiment.In contrast,the glutathione(GSH)content was increased at 24 h and 48 h of exposure and decreased at 96 h.Moreover,a significant increase in malondialdehyde(MDA)level was observed in T.thermophila after96 h of exposure.Furthermore,PYR upregulated the HSP703,HSP705,GPx2,and ABAC15 gene expression in the 0.1–5-mg/L groups and downregulated the HSP704,HSP90,TGR,and ABCC52 mRNA levels at 96 h of exposure.These results suggest that PYR may exert adverse effects on T.thermophila by inducing oxidative stress and changing the gene expression related to ABC transporters and stress,which may enrich the understanding of the toxicity mechanism of PYR in aquatic organisms and provide reference data for aquatic ecological risk assessments.
Yang LIUJiale ZHANGPeng XIAOXin LIUYisifu MAJing ZHANGBangjun ZHANG
Meiosis is a critical cell division program that produces haploid gametes for sexual reproduction.Abnormalities in meiosis are often causes of infertility and birth defects(e.g.,Down syndrome).Most organisms use a highly specialized zipper-like protein complex,the synaptonemal complex(SC),to guide and stabilize pairing of homologous chromosomes in meiosis.Although the SC is critical for meiosis in many eukaryotes,there are organisms that perform meiosis without a functional SC.However,such SC-less meiosis is poorly characterized.To understand the features of SC-less meiosis and its adaptive significance,the ciliated protozoan Tetrahymena was selected as a model.Meiosis research in Tetrahymena has revealed intriguing aspects of the regulatory programs utilized in its SC-less meiosis,yet additional efforts are needed for obtaining an in-depth comprehension of mechanisms that are associated with the absence of SC.Here,aiming at promoting a wider application of Tetrahymena for meiosis research,we introduce basic concepts and core techniques for studying meiosis in Tetrahymena and then suggest future directions for expanding the current Tetrahymena meiosis research toolbox.These methodologies could be adopted for dissecting meiosis in poorly characterized ciliates that might reveal novel features.Such data will hopefully provide insights into the function of the SC and the evolution of meiosis from a unique perspective.
Clipping of the histone H3 N-terminal tail has been implicated in multiple fundamental biological processes for a growing list of eukaryotes.H3 clipping,serving as an irreversible process to permanently remove some post-translational modifications(PTMs),may lead to noticeable changes in chromatin dynamics or gene expression.The eukaryotic model organism Tetrahymena thermophila is among the first few eukaryotes that exhibits H3 clipping activity,wherein the first six amino acids of H3 are cleaved off during vegetative growth.Clipping only occurs in the transcriptionally silent micronucleus of the binucleated T.thermophila,thus offering a unique opportunity to reveal the role of H3 clipping in epigenetic regulation.However,the physiological functions of the truncated H3 and its protease(s)for clipping remain elusive.Here,we review the major findings of H3 clipping in T.thermophila and highlight its association with histone modifications and cell cycle regulation.We also summarize the functions and mechanisms of H3 clipping in other eukaryotes,focusing on the high diversity in terms of protease families and cleavage sites.Finally,we predict several protease candidates in T.thermophila and provide insights for future studies.
Fan WeiBo PanJinghan DiaoYuanyuan WangYalan ShengShan Gao
