LF4/MOK and a CDK-related kinase regulate the number and length of cilia in Tetrahymena

The length of cilia is controlled by a poorly understood mechanism that involves members of the conserved RCK kinase group, and among them, the LF4/MOK kinases. The multiciliated protist model, Tetrahymena, carries two types of cilia (oral and locomotory) and the length of the locomotory cilia is dependent on their position with the cell. In Tetrahymena, loss of an LF4/MOK ortholog, LF4A, lengthened the locomotory cilia, but also reduced their number. Without LF4A, cilia assembled faster and showed signs of increased intraflagellar transport (IFT). Consistently, overproduced LF4A shortened cilia and downregulated IFT. GFP-tagged LF4A, expressed in the native locus and imaged by total internal reflection microscopy, was enriched at the basal bodies and distributed along the shafts of cilia. Within cilia, most LF4A-GFP particles were immobile and a few either diffused or moved by IFT. We suggest that the distribution of LF4/MOK along the cilium delivers a uniform dose of inhibition to IFT trains that travel from the base to the tip. In a longer cilium, the IFT machinery may experience a higher cumulative dose of inhibition by LF4/MOK. Thus, LF4/MOK activity could be a readout of cilium length that helps to balance the rate of IFT-driven assembly with the rate of disassembly at steady state. We used a forward genetic screen to identify a CDK-related kinase, CDKR1, whose loss-of-function suppressed the shortening of cilia caused by overexpression of LF4A, by reducing its kinase activity. Loss of CDKR1 alone lengthened both the locomotory and oral cilia. CDKR1 resembles other known ciliary CDK-related kinases: LF2 of Chlamydomonas, mammalian CCRK and DYF-18 of C. elegans, in lacking the cyclin-binding motif and acting upstream of RCKs. The new genetic tools we developed here for Tetrahymena have potential for further dissection of the principles of cilia length regulation in multiciliated cells.

DNA double-strand break formation and repair in Tetrahymena meiosis

The molecular details of meiotic recombination have been determined for a small number of model organisms. From these studies, a general picture has emerged that shows that most, if not all, recombination is initiated by a DNA double-strand break (DSB) that is repaired in a recombinogenic process using a homologous DNA strand as a template. However, the details of recombination vary between organisms, and it is unknown which variant is representative of evolutionarily primordial meiosis or most prevalent among eukaryotes. To answer these questions and to obtain a better understanding of the range of recombination processes among eukaryotes, it is important to study a variety of different organisms. Here, the ciliate Tetrahymena thermophila is introduced as a versatile meiotic model system, which has the additional bonus of having the largest phylogenetic distance to all of the eukaryotes studied to date. Studying this organism can contribute to our understanding of the conservation and diversification of meiotic recombination processes.

Autophagy prevents autophagic cell death in Tetrahymena in response to oxidative stress

Autophagy is a major cellular pathway used to degrade long-lived proteins or organelles that may be damaged due to increased reactive oxygen species (ROS) generated by cellular stress. Autophagy typically enhances cell survival, but it may also act to promote cell death under certain conditions. The mechanism underlying this paradox, however, remains unclear. We showed that Tetrahymena cells exerted increased membrane-bound vacuoles characteristic of autophagy followed by autophagic cell death (referred to as cell death with autophagy) after exposure to hydrogen peroxide. Inhibition of autophagy by chloroquine or 3-methyladenine significantly augmented autophagic cell death induced by hydrogen peroxide. Blockage of the mitochondrial electron transport chain or starvation triggered activation of autophagy followed by cell death by inducing the production of ROS due to the loss of mitochondrial membrane potential. This indicated a regulatory role of mitochondrial ROS in programming autophagy and autophagic cell death in Tetrahymena. Importantly, suppression of autophagy enhanced autophagic cell death in Tetrahymena in response to elevated ROS production from starvation, and this was reversed by antioxidants. Therefore, our results suggest that autophagy was activated upon oxidative stress to prevent the initiation of autophagic cell death in Tetrahymena until the accumulation of ROS passed the point of no return, leading to delayed cell death in Tetrahymena.

Biased assembly of the nuclear pore complex is required for somatic and germline nuclear differentiation in Tetrahymena

Ciliates have two functionally distinct nuclei, a somatic macronucleus (MAC) and a germline micronucleus (MIC) that develop from daughter nuclei of the last postzygotic division (PZD) during the sexual process of conjugation. Understanding this nuclear dimorphism is a central issue in ciliate biology. We show, by live-cell imaging of Tetrahymena, that biased assembly of the nuclear pore complex (NPC) occurs immediately after the last PZD, which generates anterior-posterior polarized nuclei: MAC-specific NPCs assemble in anterior presumptive MACs but not in posterior presumptive MICs. MAC-specific NPC assembly in the anterior nuclei occurs much earlier than transport of Twi1p, which is required for MAC genome rearrangement. Correlative light-electron microscopy shows that addition of new nuclear envelope (NE) precursors occurs through the formation of domains of redundant NE, where the outer double membrane contains the newly assembled NPCs. Nocodazole inhibition of the second PZD results in assembly of MAC-specific NPCs in the division-failed zygotic nuclei, leading to failure of MIC differentiation. Our findings demonstrate that NPC type switching has a crucial role in the establishment of nuclear differentiation in ciliates.

Msh4 and Msh5 function in SC-independent chiasma formation during the streamlined meiosis of Tetrahymena

ZMM proteins have been defined in budding yeast as factors that are collectively involved in the formation of interfering crossovers (COs) and synaptonemal complexes (SCs), and they are a hallmark of the predominant meiotic recombination pathway of most organisms. In addition to this so-called class I CO pathway, a minority of crossovers are formed by a class II pathway, which involves the Mus81-Mms4 endonuclease complex. This is the only CO pathway in the SC-less meiosis of the fission yeast. ZMM proteins (including SC components) were always found to be co-occurring and hence have been regarded as functionally linked. Like the fission yeast, the protist Tetrahymena thermophila does not possess a SC, and its COs are dependent on Mus81-Mms4. Here we show that the ZMM proteins Msh4 and Msh5 are required for normal chiasma formation, and we propose that they have a pro-CO function outside a canonical class I pathway in Tetrahymena. Thus, the two-pathway model is not tenable as a general rule.

Abandoning sex: multiple origins of asexuality in the ciliate Tetrahymena

BACKGROUND

By segregating somatic and germinal functions into large, compound macronuclei and small diploid micronuclei, respectively, ciliates can explore sexuality in ways other eukaryotes cannot. Sex, for instance, is not for reproduction but for nuclear replacement in the two cells temporarily joined in conjugation. With equal contributions from both conjugants, there is no cost of sex which theory predicts should favor asexuality. Yet ciliate asexuality is rare. The exceptional Tetrahymena has abandoned sex through loss of the micronucleus; its amicronucleates are abundant in nature where they reproduce by binary fission but never form conjugating pairs. A possible reason for their abundance is that the Tetrahymena macronucleus does not accumulate mutations as proposed by Muller's ratchet. As such, Tetrahymena amicronucleates have the potential to be very old. This study used cytochrome oxidase-1 barcodes to determine the phylogenetic origin and relative age of amicronucleates isolated from nature.

RESULTS

Amicronucleates constituted 25% of Tetrahymena-like wild isolates. Of the 244 amicronucleates examined for cox1 barcodes, 237 belonged to Tetrahymena, seven to other genera. Sixty percent originated from 12 named species or barcoded strains, including the model Tetrahymena thermophila, while the remaining 40% represent 19 putative new species, eight of which have micronucleate counterparts and 11 of which are known only as amicronucleates. In some instances, cox1 haplotypes were shared among micronucleate and amicronucleates collected from the same source. Phylogenetic analysis showed that most amicronucleates belong to the "borealis" clade in which mating type is determined by gene rearrangement. Some amicronucleate species were clustered on the SSU phylogenetic tree and had longer branch lengths, indicating more ancient origin.

CONCLUSIONS

Naturally occurring Tetrahymena amicronucleates have multiple origins, arising from numerous species. Likely many more new species remain to be discovered. Shared haplotypes indicate that some are of contemporary origin, while phylogeny indicates that others may be millions of years old. The apparent success of amicronucleate Tetrahymena may be because macronuclear assortment and recombination allow them to avoid Muller's ratchet, incorporate beneficial mutations, and evolve independently of sex. The inability of amicronucleates to mate may be the result of error(s) in mating type gene rearrangement.

A single cohesin complex performs mitotic and meiotic functions in the protist tetrahymena

The cohesion of sister chromatids in the interval between chromosome replication and anaphase is important for preventing the precocious separation, and hence nondisjunction, of chromatids. Cohesion is accomplished by a ring-shaped protein complex, cohesin; and its release at anaphase occurs when separase cleaves the complex's α-kleisin subunit. Cohesin has additional roles in facilitating DNA damage repair from the sister chromatid and in regulating gene expression. We tested the universality of the present model of cohesion by studying cohesin in the evolutionarily distant protist Tetrahymena thermophila. Localization of tagged cohesin components Smc1p and Rec8p (the α-kleisin) showed that cohesin is abundant in mitotic and meiotic nuclei. RNAi knockdown experiments demonstrated that cohesin is crucial for normal chromosome segregation and meiotic DSB repair. Unexpectedly, cohesin does not detach from chromosome arms in anaphase, yet chromosome segregation depends on the activity of separase (Esp1p). When Esp1p is depleted by RNAi, chromosomes become polytenic as they undergo multiple rounds of replication, but fail to separate. The cohesion of such bundles of numerous chromatids suggests that chromatids may be connected by factors in addition to topological linkage by cohesin rings. Although cohesin is not detected in transcriptionally active somatic nuclei, its loss causes a slight defect in their amitotic division. Notably, Tetrahymena uses a single version of α-kleisin for both mitosis and meiosis. Therefore, we propose that the differentiation of mitotic and meiotic cohesins found in most other model systems is not due to the need of a specialized meiotic cohesin, but due to additional roles of mitotic cohesin.

Effects of the aquatic contaminant human pharmaceuticals and their mixtures on the proliferation and migratory responses of the bioindicator freshwater ciliate Tetrahymena

An increasing attention is paid to the potential harmful effects of aquatic contaminant pharmaceuticals exerted on both biosystems and humans. In the present work the effects of 14 pharmaceuticals including NSAIDs, antibiotics, β-blockers and a frequently used X-ray contrast media on the proliferation and migratory behavior of the freshwater ciliate Tetrahymena pyriformis was investigated. Moreover, the mixture toxicity of four selected pharmaceuticals (diclofenac, ibuprofen, metoprolol and propranolol) was evaluated in binary mixtures using full factorial experimental design. Our results showed that the sensitivity of Tetrahymena to NSAIDs and β-blockers (EC(50) ranged from 4.8 mg L(-1) to 308.1 mg L(-1)) was comparable to that of algal or Daphnia bioassays. Based on these elevated EC(50) values acute toxic effects of these pharmaceuticals to T. pyriformis are unlikely. Antibiotics and the contrast agent sodium-diatrizoate had no proliferation inhibiting effect. Chemotactic response of Tetrahymena was more sensible than proliferation as significant chemorepellent action was observed in the environmentally realistic concentration range for acetylsalicylic acid, diclofenac, fenoprofen, paracetamol, metoprolol, propranolol, timolol and trimethoprim (Chemotaxis Index ranged from 63% to 88%). Mixture toxicity experiments resulted in a complex, concentration dependent interaction type pattern with antagonism being the predominant interaction type (59%) followed by additivity (37%) and synergism (4%). Hence the concept of concentration addition validated for NSAIDs in other organisms cannot be adopted for this ciliate. In summary authors suggest Tetrahymena as a sensible model of testing aquatic contaminants as well as underline the significance using more specific endpoints to understand the complex mechanisms investigated.

Predation influences the structure of biofilm developed on ultrafiltration membranes

This study investigates the impact of predation by eukaryotes on the development of specific biofilm structures in gravity-driven dead-end ultrafiltration systems. Filtration systems were operated under ultra-low pressure conditions (65 mbar) without the control of biofilm formation. Three different levels of predation were evaluated: (1) inhibition of eukaryotic organisms, (2) addition of cultured protozoa (Tetrahymena pyriformis), and (3) no modification of microbial community as a control. The system performance was evaluated based on permeate flux and structures of the biofilm. It was found that predation had a significant influence on both the total amount and also the structure of the biofilm. An open and heterogeneous structure developed in systems with predation whereas a flat, compact, and thick structure that homogeneously covered the membrane surface developed in absence of predation. Permeate flux was correlated with the structure of the biofilm with increased fluxes for smaller membrane coverage. Permeate fluxes in the presence or absence of the predators was 10 and 5 L m(-2) h(-1), respectively. It was concluded that eukaryotic predation is a key factor influencing the performance of gravity-driven ultrafiltration systems.

A simple microscopy assay to teach the processes of phagocytosis and exocytosis

Phagocytosis and exocytosis are two cellular processes involving membrane dynamics. While it is easy to understand the purpose of these processes, it can be extremely difficult for students to comprehend the actual mechanisms. As membrane dynamics play a significant role in many cellular processes ranging from cell signaling to cell division to organelle renewal and maintenance, we felt that we needed to do a better job of teaching these types of processes. Thus, we developed a classroom-based protocol to simultaneously study phagocytosis and exocytosis in Tetrahymena pyriformis. In this paper, we present our results demonstrating that our undergraduate classroom experiment delivers results comparable with those acquired in a professional research laboratory. In addition, students performing the experiment do learn the mechanisms of phagocytosis and exocytosis. Finally, we demonstrate a mathematical exercise to help the students apply their data to the cell. Ultimately, this assay sets the stage for future inquiry-based experiments, in which the students develop their own experimental questions and delve deeper into the mechanisms of phagocytosis and exocytosis.

The recombinases Rad51 and Dmc1 play distinct roles in DNA break repair and recombination partner choice in the meiosis of Tetrahymena

Repair of programmed DNA double-strand breaks (DSBs) by meiotic recombination relies on the generation of flanking 3' single-stranded DNA overhangs and their interaction with a homologous double-stranded DNA template. In various common model organisms, the ubiquitous strand exchange protein Rad51 and its meiosis-specific homologue Dmc1 have been implicated in the joint promotion of DNA-strand exchange at meiotic recombination sites. However, the division of labor between these two recombinases is still a puzzle. Using RNAi and gene-disruption experiments, we have studied their roles in meiotic recombination and chromosome pairing in the ciliated protist Tetrahymena as an evolutionarily distant meiotic model. Cytological and electrophoresis-based assays for DSBs revealed that, without Rad51p, DSBs were not repaired. However, in the absence of Dmc1p, efficient Rad51p-dependent repair took place, but crossing over was suppressed. Immunostaining and protein tagging demonstrated that only Dmc1p formed strong DSB-dependent foci on meiotic chromatin, whereas the distribution of Rad51p was diffuse within nuclei. This suggests that meiotic nucleoprotein filaments consist primarily of Dmc1p. Moreover, a proximity ligation assay confirmed that little if any Rad51p forms mixed nucleoprotein filaments with Dmc1p. Dmc1p focus formation was independent of the presence of Rad51p. The absence of Dmc1p did not result in compensatory assembly of Rad51p repair foci, and even artificial DNA damage by UV failed to induce Rad51p foci in meiotic nuclei, while it did so in somatic nuclei within one and the same cell. The observed interhomologue repair deficit in dmc1Δ meiosis is consistent with a requirement for Dmc1p in promoting the homologue as the preferred recombination partner. We propose that relatively short and/or transient Rad51p nucleoprotein filaments are sufficient for intrachromosomal recombination, whereas long nucleoprotein filaments consisting primarily of Dmc1p are required for interhomolog recombination.

Adaptive regulation of membrane lipids and fluidity during thermal acclimation in Tetrahymena

The free-living eukaryotic protozoan Tetrahymena is a potentially useful model for the thermoadaptive membrane regulation because of easy growth in the axenic culture, systematic isolation of subcellular organelles, and quick response to temperature stress. Exposure of Tetrahymena cells to the cold temperature induces marked alterations in the lipid composition and the physical properties (fluidity) of various membranes. The increase in fatty acid unsaturation of membrane phospholipids is required to preserve the proper fluidity. In this homeoviscous adaptive response, acyl-CoA desaturase plays a pivotal role and its activity is regulated by induction of the enzyme via transcriptional activation.

CCTalpha and CCTdelta chaperonin subunits are essential and required for cilia assembly and maintenance in Tetrahymena

Background

The eukaryotic cytosolic chaperonin CCT is a hetero-oligomeric complex formed by two rings connected back-to-back, each composed of eight distinct subunits (CCTα to CCTζ). CCT complex mediates the folding, of a wide range of newly synthesised proteins including tubulin (α, β and γ) and actin, as quantitatively major substrates.

Methodology/Principal Findings

We disrupted the genes encoding CCTα and CCTδ subunits in the ciliate Tetrahymena. Cells lacking the zygotic expression of either CCTα or CCTδ showed a loss of cell body microtubules, failed to assemble new cilia and died within 2 cell cycles. We also show that loss of CCT subunit activity leads to axoneme shortening and splaying of tips of axonemal microtubules. An epitope-tagged CCTα rescued the gene knockout phenotype and localized primarily to the tips of cilia. A mutation in CCTα, G346E, at a residue also present in the related protein implicated in the Bardet Biedel Syndrome, BBS6, also caused defects in cilia and impaired CCTα localization in cilia.

Conclusions/Significance

Our results demonstrate that the CCT subunits are essential and required for ciliary assembly and maintenance of axoneme structure, especially at the tips of cilia.

Tetrahymena meiotic nuclear reorganization is induced by a checkpoint kinase-dependent response to DNA damage

In the ciliate Tetrahymena, meiotic micronuclei (MICs) undergo extreme elongation, and meiotic pairing and recombination take place within these elongated nuclei (the "crescents"). We have previously shown that elongation does not occur in the absence of Spo11p-induced DNA double-strand breaks (DSBs). Here we show that elongation is restored in spo11Delta mutants by various DNA-damaging agents including ones that may not cause DSBs to a notable extent. MIC elongation following Spo11p-induced DSBs or artificially induced DNA lesions is probably a DNA-damage response mediated by a phosphokinase signal transduction pathway, since it is suppressed by the ATM/ATR kinase inhibitors caffeine and wortmannin and by knocking out Tetrahymena's ATR orthologue. MIC elongation occurs concomitantly with the movement of centromeres away from the telomeric pole of the MIC. This DNA damage-dependent reorganization of the MIC helps to arrange homologous chromosomes alongside each other but is not sufficient for exact pairing. Thus, Spo11p contributes to bivalent formation in two ways: by creating a favorable spatial disposition of homologues and by stabilizing pairing by crossovers. The polarized chromosome orientation inside the crescent resembles the conserved meiotic bouquet, and crescent and bouquet also share the putative function of aiding meiotic pairing. However, they are regulated differently because in Tetrahymena, DSBs are required for entering rather than exiting this stage.

Abnormal micronuclear telomeres lead to an unusual cell cycle checkpoint and defects in Tetrahymena oral morphogenesis

Telomere mutants have been well studied with respect to telomerase and the role of telomere binding proteins, but they have not been used to explore how a downstream morphogenic event is related to the mutated telomeric DNA. We report that alterations at the telomeres can have profound consequences on organellar morphogenesis. Specifically, a telomerase RNA mutation termed ter1-43AA results in the loss of germ line micronuclear telomeres in the binucleate protozoan Tetrahymena thermophila. These cells also display a micronuclear mitotic arrest, characterized by an extreme delay in anaphase with an elongated, condensed chromatin and a mitotic spindle apparatus. This anaphase defect suggests telomere fusions and consequently a spindle rather than a DNA damage checkpoint. Most surprisingly, these mutants exhibit unique, dramatic defects in the formation of the cell's oral apparatus. We suggest that micronuclear telomere loss leads to a "dynamic pause" in the program of cortical development, which may reveal an unusual cell cycle checkpoint.

An overview of techniques for immobilizing and viewing living cells

Microscopists making observations on living cells are often faced with the challenge of getting those cells to hold still for extended observation times. This paper presents an overview/summary of a range of techniques for non-destructive immobilization of living cells (with an emphasis on protozoa), permitting microscopic observations and photography. A variety of chemical and physical immobilization techniques are discussed, but particular attention is paid to a comparative discussion of the mechanical devices (rotocompressors or microcompressors) used for reversible trapping of living cells.

TIF1 activates the intra-S-phase checkpoint response in the diploid micronucleus and amitotic polyploid macronucleus of Tetrahymena

The ribosomal DNA origin binding protein Tif1p regulates the timing of rDNA replication and is required globally for proper S-phase progression and division of the Tetrahymena thermophila macronucleus. Here, we show that Tif1p safeguards chromosomes from DNA damage in the mitotic micronucleus and amitotic macronucleus. TIF1p localization is dynamically regulated as it moves into the micro- and macronucleus during the respective S phases. TIF1 disruption mutants are hypersensitive to hydroxyurea and methylmethanesulfonate, inducers of DNA damage and intra-S-phase checkpoint arrest in all examined eukaryotes. TIF1 mutants incur double-strand breaks in the absence of exogenous genotoxic stress, destabilizing all five micronuclear chromosomes. Wild-type Tetrahymena elicits an intra-S-phase checkpoint response that is induced by hydroxyurea and suppressed by caffeine, an inhibitor of the apical checkpoint kinase ATR/MEC1. In contrast, hydroxyurea-challenged TIF1 mutants fail to arrest in S phase or exhibit caffeine-sensitive Rad51 overexpression, indicating the involvement of TIF1 in checkpoint activation. Although aberrant micro- and macronuclear division occurs in TIF1 mutants and caffeine-treated wild-type cells, TIF1p bears no similarity to ATR or its substrates. We propose that TIF1 and ATR function in the same epistatic pathway to regulate checkpoint responses in the diploid mitotic micronucleus and polyploid amitotic macronucleus.

Microbial exopolymers link predator and prey in a model yeast biofilm system

Protistan grazing on biofilms is potentially an important conduit enabling energy flow between microbial trophic levels. Contrary to the widely held assumption that protistan feeding primarily involves ingestion of biofilm cells, with negative consequences for the biofilm, this study demonstrated preferential grazing on the noncellular biofilm matrix by a ciliate, with selective ingestion of yeast and bacterial cells of planktonic origin over attached and biofilm-derived planktonic cells. Introducing a ciliate to two biofilm-forming Cryptococcus species, as well as two bacterial species in a model biofilm system, fluorescent probes were applied to determine ingestion of cellular and noncellular biofilm fractions. Fluoromicroscopy, as well as photometric quantification, confirmed that protistan grazing enhanced yeast biofilm metabolism, and an increase in biofilm biomass and viability. We propose that the extracellular polymeric matrix of biofilms may act as an interface regulating interaction between predator and prey, while serving as source of nutrients and energy for protists.

RNA reprogramming of α-mannosidase mRNA sequencesin vitroby myxomycete group IC1 and IE ribozymes

Trans-splicing group I ribozymes have been introduced in order to mediate RNA reprogramming (including RNA repair) of therapeutically relevant RNA transcripts. Efficient RNA reprogramming depends on the appropriate efficiency of the reaction, and several attempts, including optimization of target recognition and ribozyme catalysis, have been performed. In most studies, the Tetrahymena group IC1 ribozyme has been applied. Here we investigate the potential of group IC1 and group IE intron ribozymes, derived from the myxomycetes Didymium and Fuligo, in addition to the Tetrahymena ribozyme, for RNA reprogramming of a mutated alpha-mannosidase mRNA sequence. Randomized internal guide sequences were introduced for all four ribozymes and used to select accessible sites within isolated mutant alpha-mannosidase mRNA from mammalian COS-7 cells. Two accessible sites common to all the group I ribozymes were identified and further investigated in RNA reprogramming by trans-splicing analyses. All the myxomycete ribozymes performed the trans-splicing reaction with high fidelity, resulting in the conversion of mutated alpha-mannosidase RNA into wild-type sequence. RNA protection analysis revealed that the myxomycete ribozymes perform trans-splicing at approximately similar efficiencies as the Tetrahymena ribozyme. Interestingly, the relative efficiency among the ribozymes tested correlates with structural features of the P4-P6-folding domain, consistent with the fact that efficient folding is essential for group I intron trans-splicing.

Optimization and validation of a colorimetric assay for Tetrahymena sp. survival

A colorimetric assay based on the reduction of 3-(4,5-dimethyl-2-thiazol-2-yl)-2,5-diphenyl-2h-tetrazolium bromide (MTT), for the quantification of Tetrahymena sp. survival is described. An increase in the concentration of Tetrahymena sp. cells from 0 to 1 x 10(6) cells/ml produced a linear (R(2)=0.9965) increase in the optical density (OD, 570-630 nm), and dead cells (pre-exposed to 250 mg/l formalin for 4 h) did not produce a background reading. Cells exposed to sublethal concentrations to formalin (100 mg/l or less for 4 h) recovered their growth. Using the MTT assay, we determined that Tetrahymena sp. is sensitive to formalin, chloramine-T, hydrogen peroxide, copper sulfate and NaCl. The sensitivity increased with increasing chemical concentrations and exposure time. Tetrahymena sp. was resistant to bromex and malachite green. The use of this assay in drug screening for the development of treatments for tetrahymenosis and as a bioassay to evaluate the toxicity of environmental toxicants is discussed.

Multiple tubulin forms in ciliated protozoan Tetrahymena and Paramecium species

Tetrahymena and Paramecium species are widely used representatives of the phylum Ciliata. Ciliates are particularly suitable model organisms for studying the functional heterogeneity of tubulins, since they provide a wide range of different microtubular structures in a single cell. Sequencing projects of the genomes of members of these two genera are in progress. Nearly all members of the tubulin superfamily (alpha-, beta-, gamma-, delta-, epsilon-, eta-, theta-, iota-, and kappa-tubulins) have been identified in Paramecium tetraurelia. In Tetrahymena spp., the functional consequences of different posttranslational tubulin modifications (acetylation, tyrosination and detyrosination, phosphorylation, glutamylation, and glycylation) have been studied by different approaches. These model organisms provide the opportunity to determine the function of tubulins found in ciliates, as well as in humans, but absent in some other model organisms. They also give us an opportunity to explore the mechanisms underlying microtubule diversity. Here we review current knowledge concerning the diversity of microtubular structures, tubulin genes, and posttranslational modifications in Tetrahymena and Paramecium species.

Core formation and the acquisition of fusion competence are linked during secretory granule maturation in Tetrahymena

The formation of dense core secretory granules is a multistage process beginning in the trans Golgi network and continuing during a period of granule maturation. Direct interactions between proteins in the membrane and those in the forming dense core may be important for sorting during this process, as well as for organizing membrane proteins in mature granules. We have isolated two mutants in dense core granule formation in the ciliate Tetrahymena thermophila, an organism in which this pathway is genetically accessible. The mutants lie in two distinct genes but have similar phenotypes, marked by accumulation of a set of granule cargo markers in intracellular vesicles resembling immature secretory granules. Sorting to these vesicles appears specific, since they do not contain detectable levels of an extraneous secretory marker. The mutants were initially identified on the basis of aberrant proprotein processing, but also showed defects in the docking of the immature granules. These defects, in core assembly and docking, were similarly conditional with respect to growth conditions, and therefore are likely to be tightly linked. In starved cells, the processing defect was less severe, and the immature granules could dock but still did not undergo stimulated exocytosis. We identified a lumenal protein that localizes to the docking-competent end of wildtype granules, but which is delocalized in the mutants. Our results suggest that dense cores have functionally distinct domains that may be important for organizing membrane proteins involved in docking and fusion.

A Dicer-like protein in Tetrahymena has distinct functions in genome rearrangement, chromosome segregation, and meiotic prophase

Previous studies indicated that genome rearrangement involving DNA sequence elimination that occurs at late stages of conjugation in Tetrahymena is epigenetically controlled by siRNA-like scan (scn) RNAs produced from nongenic, heterogeneous, bidirectional, micronuclear transcripts synthesized at early stages of conjugation. Here, we show that Dcl1p, one of three Tetrahymena Dicer-like enzymes, is required for processing the micronuclear transcripts to scnRNAs. DCL1 is also required for methylation of histone H3 at Lys 9, which, in wild-type cells, specifically occurs on the sequences (IESs) being eliminated. These results argue that Dcl1p processes nongenic micronuclear transcripts to scnRNAs and is required for IES elimination. This is the first evidence linking nongenic micronuclear transcripts, scnRNAs, and genome rearrangement. Dcl1p also is required for proper mitotic and meiotic segregation of micronuclear chromosomes and for normal chromosome alignment in meiotic prophase, suggesting that DCL1 has multiple functions in regulating chromosome dynamics.

Localization by indirect immunofluorescence of tetrin, actin, and centrin to the oral apparatus and buccal cavity of the macrostomal form of Tetrahymena vorax

We have taken advantage of the size of the macrostomal oral apparatus of Tetrahymena vorax to investigate the immunofluorescent localization of three cytoskeletal proteins--tetrin, actin, and centrin. Tetrin and actin antibodies co-localize to cross-connectives that anchor the membranelles. These antibodies also recognize the coarse filamentous reticulum, a filament associated with the undulating membrane. Actin-specific localization extends beyond the coarse filamentous reticulum-undulating membrane complex into a region called the specialized cytoplasm. A centrin antibody localizes to the fine filamentous reticulum which, along with microtubules of the oral ribs, circumscribes the cytostomal opening. Models of phagocytic contraction based on these data are presented.

Caspase-like activity in programmed nuclear death during conjugation of Tetrahymena thermophila

Apoptosis, or programmed cell death, is common in a variety of eucaryotes, from unicellular protozoa to vertebrates. The ciliated protozoan Tetrahymena thermophila has a unique apoptosis-like nuclear death during conjugation, called programmed nuclear death. This death program involves nuclear condensation (pyknosis) and oligonucleosomal DNA fragmentation in the parental macronucleus. Subsequently, the condensed nucleus is entirely resorbed in the autophagosome. Here we demonstrate that caspase-8- and -9-like activity was detected, but no caspase-3-like activity, by in vitro assay during the nuclear resorption process, suggesting that caspase-like activity is associated with both programmed cell death and apoptosis-like nuclear death in Tetrahymena. The use of indicator dye to detect the loss of mitochondrial membrane potential suggested the uptake of mitochondria and the degenerating macronucleus by the autophagosome. An involvement of mitochondria in the programmed nuclear death is discussed.

Novel cytoskeletal proteins in the cortex of Tetrahymena

An important unsolved problem lies in the mechanisms that determine overall size, shape, and the localization of subcellular structures in eukaryotic cells. The membrane skeleton must play a central role in these processes in many cell types, and the ciliate membrane skeleton, or epiplasm, offers favorable opportunities for exploring the molecular determinants of cortical organization. Among the ciliates, Tetrahymena is well suited for the application of a wide range of molecular and cellular approaches. Progress has been made in the identification and sequencing of genes and proteins that encode epiplasmic and cortical proteins. The amino acid sequences of these proteins suggest that they define new classes of cytoskeletal proteins, distinct from the articulin and epiplasmin proteins. We will also discuss recent in vivo and in vitro studies of the regulation of assembly of these cortical proteins. This will include information regarding the down-regulation of epiplasmic proteins during cleavage, their topographic regulation in the cell cycle, and the results of in vitro assembly and binding studies of the epiplasmic C protein.

Inner arm dynein 1 is essential for Ca++-dependent ciliary reversals in Tetrahymena thermophila

Cilia in many organisms undergo a phenomenon called ciliary reversal during which the cilia reverse the beat direction, and the cell swims backwards. Ciliary reversal is typically caused by a depolarizing stimulus that ultimately leads to a rise in intraciliary Ca++ levels. It is this increase in intraciliary Ca++ that triggers ciliary reversal. However, the mechanism by which an increase in intraciliary Ca++ causes ciliary reversal is not known. We have previously mutated the DYH6 gene of Tetrahymena thermophila by targeted gene knockout and shown that the knockout mutants (KO6 mutants) are missing inner arm dynein 1 (I1). In this study, we show that KO6 mutants do not swim backward in response to depolarizing stimuli. In addition to being unable to swim backwards, KO6 mutants swim forward at approximately one half the velocity of wild-type cells. However, the ciliary beat frequency in KO6 mutants is indistinguishable from that of wild-type cells, suggesting that the slow forward swimming of KO6 mutants is caused by an altered waveform rather than an altered beat frequency. Live KO6 cells are also able to increase and decrease their swim speeds in response to stimuli, suggesting that some aspects of their swim speed regulation mechanisms are intact. Detergent-permeabilized KO6 mutants fail to undergo Ca++-dependent ciliary reversals and do not show Ca++-dependent changes in swim speed after MgATP reactivation, indicating that the axonemal machinery required for these responses is insensitive to Ca++ in KO6 mutants. We conclude that Tetrahymena inner arm dynein 1 is not only an essential part of the Ca++-dependent ciliary reversal mechanism but it also may contribute to Ca++-dependent changes in swim speed and to the formation of normal waveform during forward swimming.

High mortality due to Tetrahymena sp. infection in laboratory-maintained zebrafish (Brachydanio rerio)

A large colony of laboratory zebrafish (Brachydanio rerio) used in the study of early vertebrate embryogenesis began experiencing acute, unexplained mortality that approached 100% among approximately 30-day-old resident fry. The initial differential diagnosis included ammonia, nitrite, or chlorine toxicosis, as well as iatrogenically induced toxicosis associated with improper sanitation procedures of laboratory equipment. Necropsy of dead and moribund fry prior to fixation revealed swarms of ovoid-shaped, motile, ciliated protozoa with a "spiraling football" motion. Wet mount preparations of various water samples also contained high numbers of similar protozoa. Histologic examination of affected fry revealed numerous, periodic acid-Schiff-positive forms within the body coelom, and epithelial and muscle tissues. The protozoa were consistent morphologically with members of the genus Tetrahymena, which is usually a free-living, nonpathogenic ciliated protozoa in fresh and saltwater environments. Relevant disease associated with Tetrahymena spp. in viviparous fish has been reported as a result of concurrent disease, immunosuppression, or poor water quality conditions. To the authors' knowledge, this is the first report of an epizootic involving laboratory maintained zebrafish, and the diagnostic course and therapeutic interventions undertaken to alleviate Tetrahymena species-associated clinical disease.

Phenotype switching in polymorphic Tetrahymena: a single-cell Jekyll and Hyde

For nearly half a century, phenotype switching in the group of polymorphic species of the ciliate genus Tetrahymena has been the subject of investigations of the underlying mechanisms, the accompanying biochemical and structural changes, and the evolution of polymorphic survival strategy. Beginning with the pioneering systematic studies by Furgason in 1940 of hymenostome ciliates, the experimental approach rapidly expanded to include investigations of growth, nutrition, physiology, morphology, and morphogenesis in the polymorphic species. Recently, with progress in elucidation of the novel signaling ligand and identification of elements of the subsequent signal transduction cascade, in addition to the growing catalog of intracellular events associated with differentiation in these unicellular eukaryotes, we have begun to address the mechanistic basis of polymorphism. This review summarizes and integrates the history and recent discoveries concerning Tetrahymena polymorphic cells. We are now poised to answer fundamental questions about this interesting pathway of cell differentiation.

Cisplatin induces modifications in the development of cell surface patterns of ciliates

Cisplatin [cis-dichlorodiammineplatinum (II)] brings about significant quantitative modifications in the development of cell surface patterns in two unrelated ciliates: Stylonychia and Tetrahymena. Cells cultured in the presence of cisplatin exhibit the formation of supernumerary surface structures in the form of extra cilia/cirri (fused cilia) and other organized ciliary organelles. The metal-induced formation of extra primordia and their differentiation into supernumerary ciliary structures is governed by the normal rules of development. Additional structures are accommodated within the framework of a defined pattern, suggesting the existence of an overall global control of pattern formation. The modified pattern is rectified to its normal state during post-treatment fission cycles, suggesting the role of the cell membrane in correcting developmental errors.

p85 binds to G-actin in a Ca(2+)/calmodulin-dependent manner, thus regulating the initiation of cytokinesis in tetrahymena

Tetrahymena p85 is localized to the presumptive division plane before the formation of contractile ring microfilaments. p85 binds to calmodulin in a Ca(2+)-dependent manner and both proteins colocalize to the division furrow. Inhibition of the binding of p85 and Ca(2+)/calmodulin prevents both the localization of p85 and calmodulin to the division plane and the formation of the contractile ring, suggesting that the interaction of p85 and Ca(2+)/calmodulin is important in the formation of the contractile ring. We investigated the mechanisms of the formation of contractile ring, and the relationship among p85, CaM, and actin using co-sedimentation assay: p85 binds to G-actin in a Ca(2+)/calmodulin-dependent manner, but does not bind to F-actin. Therefore, we propose that a Ca(2+)/calmodulin signal and its target protein p85 are cooperatively involved in the recruitment of G-actin to the division plane and the formation of the contractile ring.

Determination of division plane and organization of contractile ring in Tetrahymena

In the molecular mechanism of division plane determination and contractile ring formation, Tetrahymena 85kDa protein (p85) is localized to the presumptive division plane before the formation of the contractile ring. p85 directly interacts with Tetrahymena calmodulin (CaM) in a Ca2+-dependent manner, and p85 and CaM colocalize in the division furrow. A Ca2+/CaM inhibitor N-(6-Aminohexyl)-5-chloro-1-naphthalenesulfonamide HCI (W7) inhibits the direct interaction between p85 and Ca2+/CaM. W7 also inhibits the localization of p85 and CaM to the division plane, and the formation of the contractile ring and division furrow. In addition, p85 binds to G-actin in a Ca2+/CaM dependent manner, but does not bind F-actin. Tetrahymena profilin is localized to division furrow and binds Tetrahymena elongation factor-1alpha (EF-1alpha). EF-1alpha, which induces bundling of Tetrahymena F-actin, is also localized to the division furrow during cytokinesis. The evidence also indicates that Ca2+/CaM inhibits the F-actin-bundling activity of EF-1alpha, and that EF-1alpha and CaM colocalize in the division furrow. In this review, we propose that the Ca2+/CaM signal and its target protein p85 cooperatively regulate the determination of the division plane and the initiation of the contractile ring formation, and that profilin and a Ca2+/CaM-sensitive actin-bundling protein, EF-1alpha, play pivotal roles in regulating the organization of the contractile ring microfilaments.

Development in electrofused conjugants of tetrahymena thermophila

Electric shock can create parabiotic fusions of living Tetrahymena cells. In this study, cells were mated and successful pairs were electrofused with either vegetatively growing cells or other mating pairs. In particular, we electrofused pairs from normal [diploid x diploid] matings with vegetatively dividing cells in G- or M-phase of the cell cycle. We also fused [diploid x diploid] conjugants with mating pairs involving an aneuploid partner [diploid x "star"], which typically undergo an abortive conjugal pathway termed genomic exclusion. Using such parabiotic fusions we identified and characterized two developmentally critical landmarks: 1) the "abort" signal, which is initiated in pairs with nuclear defects (this first becomes evident soon after the completion of Meiosis I or the beginning of Meiosis II); and 2) the "terminal commitment point", a developmental stage in normal [diploid x diploid] pairs after which conjugation no longer responds to a parabiotically transmitted abort signal (this correlates with the onset of the second postzygotic nuclear division). Finally we demonstrate that a conjugal-arrest-activity varies with the vegetative cell cycle, reaching its highest level of activity during M-phase and dropping just after cytokinesis.

A family of developmentally excised DNA elements in Tetrahymena is under selective pressure to maintain an open reading frame encoding an integrase-like protein

Tlr1 is a member of a family of approximately 20-30 DNA elements that undergo developmentally regulated excision during formation of the macronucleus in the ciliated protozoan TETRAHYMENA: Analysis of sequence internal to the right boundary of Tlr1 revealed the presence of a 2 kb open reading frame (ORF) encoding a deduced protein with similarity to retrotransposon integrases. The ORFs of five unique clones were sequenced. The ORFs have 98% sequence conservation and align without frameshifts, although one has an additional trinucleotide at codon 561. Nucleotide changes among the five clones are highly non-random with respect to the position in the codon and 93% of the nucleotide changes among the five clones encode identical or similar amino acids, suggesting that the ORF has evolved under selective pressure to preserve a functional protein. Nineteen T/C transitions in T/CAA and T/CAG codons suggest selection has occurred in the context of the TETRAHYMENA: genome, where TAA and TAG encode Gln. Similarities between the ORF and those encoding retrotransposon integrases suggest that the Tlr family of elements may encode a polynucleotide transferase. Possible roles for the protein in transposition of the elements within the micronuclear genome and/or their developmentally regulated excision from the macronucleus are discussed.

DNA methylation in ciliates: implications in differentiation processes

Much experimental evidence on the role of DNA methylation in gene expression has been reported. Here we review reports on DNA methylation in ciliated protozoa, emphasizing its implications in cell differentiation processes. Both types of methylated bases (adenine and cytosine) can be found in macronuclear DNA. The division cycle and conjugation have been studied with regard to adenine methylation, and several different functions have been assigned to the methylation changes detected in these processes. Cytosine methylation changes were analyzed during stomatogenesis of Paramecium and encystment of Colpoda inflata. A comparative analysis with other similar microbial eukaryotic differentiation processes is carried out.

A complex of iron and nucleic acid catabolites is a signal that triggers differentiation in a freshwater protozoan

The polymorphic ciliated protozoan Tetrahymena vorax can undergo differentiation from the microstomal form, which normally feeds on bacteria and other particulate matter, into the macrostomal cell type, which is capable of ingesting prey ciliates. The process is triggered by exposure of the microstome to an inducer contained in stomatin, an exudate of the prey. To establish the identity of the signal, stomatin was fractionated by combinations of cation exchange, HPLC, and TLC, and the fractions were assayed for biological activity. Although no single active fraction of purified inducer was obtained, all fractions with activity contained ferrous iron and the nucleic acid catabolites hypoxanthine (6-oxypurine) and uracil (2, 4-dioxopyrimidine), probably in a chelated form. The activity of synthetic complexes containing these three components is equivalent to stomatin. These results indicate a role for ferrous iron and its potential in chelated form to signal differentiation in certain protozoa and, perhaps, in other organisms as well.

Macronuclear division and cytokinesis in Tetrahymena

Tetrahymena contains a micronucleus and a macronucleus. The micronucleus divides with typical mitosis, while the macronucleus divides amitotically. Although the mechanism responsible for macronuclear division was previously unknown, we clarified the organization of microtubules during macronuclear division. The macronuclear microtubules dynamically changed their distribution in an organized way throughout the macronuclear division. The macronuclear microtubules and the cytoplasmic microtubules cooperatively carried out the macronuclear division. When the micronuclear division was finished, p85 appeared at the presumptive division plane prior to the cytokinesis. The p85 directly interacted with calmodulin in a Ca(2+)-dependent manner, and p85 and CaM colocalized to the division furrow during cytokinesis. Moreover, the Ca(2+)/CaM inhibitor, W7, inhibited the direct interaction between p85 and CaM, the localization of both proteins to the division plane, and the formation of the division furrow. Thus, Ca(2+)/CaM and p85 have important roles in initiation and progression of cytokinesis in Tetrahymena.

Cytokinesis in Tetrahymena: determination of division plane and organization of contractile ring

A protein, Tetrahymena p85, is localized to the presumptive division plane before the formation of the contractile ring. p85 directly interacts with Tetrahymena calmodulin (CaM) in a Ca(2+)-dependent manner, and p85 and CaM colocalize in the division furrow. A Ca(2+)/CaM inhibitor N-(6-Aminohexyl)-5-chloro-1-naphthalenesulfonamide HCl (W7) inhibits the direct interaction between p85 and Ca(2+)/CaM. W7 also inhibits the localization of p85 and CaM to the division plane, and the formation of the contractile ring and division furrow. Tetrahymena fimbrin and elongation factor-1a (EF-1alpha), which induce bundling of Tetrahymena F-actin, are also localized to the division furrow during cytokinesis. The Tetrahymena fimbrin has two actin-binding domains, but lacks the EF-hand Ca(2+)-binding motif, suggesting that Tetrahymena fimbrin probably cross-links actin filaments in a Ca(2+)- insensitive manner during cytokinesis. The evidence also indicates that Ca(2+)/CaM inhibits the F-actin-bundling activity of EF-1alpha; and EF-1alpha and CaM colocalize in the division furrow. In this review, we propose that the Ca(2+)/CaM signal and its target protein p85 cooperatively regulate the determination of the division plane, and that a Ca(2+)-insensitive actin-bundling protein, Tetrahymena fimbrin, and a Ca(2+)/CaM-sensitive actin-bundling protein, EF-1alpha, play pivotal roles in regulating the organization of the contractile ring microfilaments.

Parental expression of the chromodomain protein Pdd1p is required for completion of programmed DNA elimination and nuclear differentiation

Thousands of DNA elimination events occur during somatic differentiation of many ciliated protozoa. In Tetrahymena, the eliminated DNA aggregates into submacronuclear structures containing the protein Pdd1p, a member of the chromodomain family. We disrupted somatic copies of PDD1, eliminating parental expression of the gene early in the sexual phase of the life cycle. Even though zygotic expression, from the undisrupted germline PDD1 copy, is activated before DNA elimination normally occurs, the somatic knockout cells suffer defects in DNA elimination, genome endoduplication, and nuclear resorption, and eventually die, demonstrating that PDD1 is essential and suggesting Pdd1p is directly involved in establishing a chromatin structure required for DNA elimination.

Molecular cloning of the gene for p85 that regulates the initiation of cytokinesis in Tetrahymena

Tetrahymena p85 is localized to the presumptive division plane before division furrow formation; its molecular weight in SDS-polyacrylamide gel electrophoresis differs in wild-type and temperature-sensitive cell-division-arrest mutant cdaA1 cells. At the restrictive temperature, p85 localization and division furrow formation are not observed in cdaA1 cells. In this study, we purified p85 and cloned a wild-type p85 cDNA. The deduced amino acid sequence of p85 was composed mainly of two kinds of repeat sequences. One of these contained regions homologous to a calmodulin-binding site and a part of actin, and the other contained a region homologous to a part of a cdc2 kinase homologue. Moreover, we cloned a cDNA encoding the cdaA1 p85. There was no difference in the predicted amino acid sequences of wild-type and cdaA1 p85, suggesting that the difference in molecular weight between p85 in wild-type and mutant cells is caused by a disorder of posttranslational-modification mechanisms of p85 in the cdaA1 cell.

The conjusome: a novel structure in Tetrahymena found only during sexual reorganization

A unique structure, the conjusome, has been identified and initially characterized in Tetrahymena thermophila. The conjusome appears only during a specific phase of conjugation. Immunofluorescence microscopy reveals that the conjusome is strongly labeled by antibodies to the protein Pdd1p. Pdd1p is a chromodomain protein and participates in the formation of chromatin-containing structures in developing macronuclear anlagen. Recent studies suggest that Pdd1p is physically associated with the elimination of specific germ-line sequences from developing macronuclei (anlagen) and may play a role in heterochromatin assembly. The conjusome contains Pdd1p, but it is devoid of any detectable DNA. The conjusome appears before DNA elimination begins in the developing anlagen and after Pdd1p is found in the parental macronucleus. Transmission electron microscopic observations reveal that the conjusome is not a membrane-bounded structure. The conjusome ranges in size from about 1 microm to sizes approaching 7 microm, depending on its maturity. It is composed of a coarse reticulum of a fibrous, electron dense material, interspersed with apparent background cytoplasm. Our initial characterization does suggest a number of possible functions for what may be a new, transient organelle.

Effect of C2 ceramide on the inositol phospholipid metabolism (uptake of 32P, 3H-serine and 3H-palmitic acid) and apoptosis-related morphological changes in Tetrahymena

Sphingomyelin metabolites have significant role in the regulation of many life processes of mammalian cells. In the present experiments the influence of phospholipid turnover and apoptosis related morphologic signs by one of this metabolite, C2 ceramide was studied, and compared to the control, untreated cells, in the unicellular Tetrahymena. The incorporation of phospholipid head group components (serine, phosphorus) show a clear time-dependence; while the incorporation of fatty acid component (palmitic acid) is very fast: no significant alterations were found between 5- and 60-min incubations. C2 ceramide treatment didn't alter 3H-palmitic acid incorporation into phospholipids, however 3H-serine incorporation was mainly inhibited. The amount of total incorporated 32P was also decreased, on the other hand the lover concentration C2 ceramide (10 microM) elevated the synthesis of inositol phospholipids. The higher concentration of C2 ceramide (50 microM) had inhibitory effect on the synthesis of each phospholipids examined. This means that in the presence of the C2 ceramide the synthesis, recovery and turnover of phospholipids, participating in signal transduction, are altered. However these observations were based the uptake of labeled phospholipid precursors, which gives information on the dynamics of the process, without using lipid mass measurements. C2 ceramide also caused the rounding off the cells, DNA degradation and nuclear condensation. These latter observations point to morphological signs of apoptosis. The results call attention to the role of sphingomyelin metabolites on signalization of unicellulars, to the cross-talk between the inositol phospholipids and sphingomyelin metabolites, and the role of these molecules in the apoptotic processes at a low evolutionary level.

Steroid hormone (hydrocortisone, oestradiol and testosterone) uptake, storage or induced synthesis in tetrahymena

After cyclodextrin-coated 10(-6) m steroid hormone treatment for 3 days (hormonal imprinting), Tetrahymena cells and their media were analysed by radioimmunoassay for the same hormone and for the presence of the other two. In the absence of hormone treatment, the cells contained no detectable levels of the three steroids. By 2 days in fresh medium following exposure of cells to a 72 h pretreatment of each specific hormone, correspondingly high quantities of hydrocortisone and oestradiol, but lesser quantities of testosterone, were found in both the media and the cells. One week after treatment only traces of hydrocortisone were found, exclusively within the cells themselves. Oestradiol was present in measurable quantities in both cells and media, whereas testosterone was only present in the medium. The presence of the other two hormones to the one used in the pretreatment were not usually present, except that when testosterone had been given, some oestradiol was also detected at 48 h, suggesting Tetrahymena has a functional cytochrome P(450)aromatase.

Accumulation of insulin-gold particles in the oral apparatus of Tetrahymena after insulin pretreatment (imprinting)

The oral apparatus and body ciliature of untreated control cells bind insulin-gold very rarely. From 1 day to 1 week after insulin pretreatment (hormonal imprinting) an enormous quantity of insulin-gold was bound by the oral cilia, completely filling the region, while the insulin-gold on the body ciliature is scattered. The binding was specific for insulin, since polyethylene glycol (PEG)-gold was not bound at all. The results call attention to the binding and the increasing role of hormonal (insulin) imprinting, and particularly to the marked role of the oral region in this binding. The roles of mucocyst extrusion and specific binding by receptors are discussed.

A telomerase mutant defective in sister chromatid separation at mitosis

The telomere is a functional domain of the chromosome, located at the extreme ends, and is essential for normal chromosome stability. Chromosomes lacking telomeres are inherited improperly, and mutations in the telomeric repeat sequences are thought to lead to senescence and possibly to cancer. The molecular mechanisms maintaining chromosomes by telomeres, however, have been unclear. Results recently reported by Kirk et al, offer an insight into new telomerase function. They have identified a novel telomerase mutation that blocks sister chromatid separation in mitosis.

Differential staining of apoptotic nuclei in living cells: application to macronuclear elimination in Tetrahymena

Acridine orange (AO) has been used as a vital fluorescent stain to identify apoptotic cells in Drosophila, but little is known about what structures are stained. We explored the specificity of AO staining while studying nuclear apoptosis in Tetrahymena. Using AO alone or together with the vital nuclear stain Hoechst 33342 (HO), we find that lysosomes are generally clustered around the degenerating nucleus and that such nuclei are stained an orange-red color, like lysosomes. Significantly, the combined dyes, more so than with AO alone, distinguish between apoptotic and normal (or necrotic) nuclei by a clear color difference. Moreover, these dyes differentially stain apoptotic and normal nuclei in avian chondrocytes. The differential staining results are nullified in fixed cells or in cytoskeletal preparations treated with RNAse. Similarly, lysosomotrophic agents eliminate the differential staining. Our results are consistent with acidification of the apoptotic nucleus, possibly by fusion with lysosomes. However, even under basic conditions, the macronucleus condenses and is eliminated, suggesting that, if the nucleus is becoming acidified, acidification by itself is not essential for nuclear elimination. The differential staining procedure may provide a useful method for specifically identifying apoptotic cells and separating them for further analysis.

Unresolvable endings: defective telomeres and failed separation

Telomeres, usually consisting of repetitive sequences and proteins bound to them, form the ends of all chromosomes, where they protect against unwanted shortening during DNA replication and cell division. The Perspective by Hawley discusses two reports, one by Kirk et al . ( p. 1478 ) of this week's issue and the other in press at Genes and Development , that point to a surprising new function for telomeres in the separation of the ends of the chromosomes during cell division.

Effects of the mammalian vasoconstrictor peptide, endothelin-1, on Tetrahymena pyriformis GL, and the immunocytological detection of endogenous endothelin-like activity

The vasoconstrictor endothelin-1 (ET-1) is shown to have significant physiological effects on a unicellular organism, Tetrahymena pyriformis. These responses include: (1) A significant increase in intracellular [Ca2+] induced by 10(-10) M ET-1; (2) Increased chemotaxis, maximal at 10(-10) M; and (3) A small inhibition of proliferation at the 10(-13)-10(-12) M concentration range. Immunocytochemical detection of endogenous ET-1 using rabbit antibodies directed against human or porcine ET-1 indicates that this is a further example of the widening group of vertebrate hormones now known to be synthesized by Tetrahymena. These observations suggest that hormones are of considerable antiquity in their phylogenetic appearance and have been highly conserved throughout evolution.