bluuebunny/crossref_metadata_2025_split huggingface dataset:
Suicide is not the inevitable outcome of “perpetual” selfing in tetrahymenines collected from natural habitats
Authors: Simon Ellen M. , Meyer E. Barbara 
Published: May 2005

AbstractA significant fraction of the Tetrahymena clones isolated from natural habitats self (mating occurs within a clone). Early attempts to study such clones failed because stable subclones were rarely, if ever, observed, and isolated pairs all died. Isozyme analysis revealed that these wild selfers were a diverse group; some were very similar to T. australis, a species with synclonal mating type determination and to T. elliotti, shown recently to have a karyonidal mating type system. One originally stable clone of T. australis included some selfing clones after a few years in our laboratory. Other clones manifested unique zymograms.Subclones isolated from 18 selfer strains were heterogeneous. All subclones of several selfers mated massively at each transfer through 100 fissions. Selfing among subclones of other selfers was highly variable or not observed. Although 77% of the pairs isolated died, and 9% of the pair cultures selfed, 15 selfers yielded some viable nonselfing “immature” progeny. Additional immature progeny were obtained by isolating pairs from macronuclear retention synclones. Although some “immature” progeny eventually selfed, most remained stable. Giemsa staining revealed macronuclear anlagen in nearly all mating pairs and some anomalies. Crosses among the F1 progeny clones of the T. elliotti selfers yield viability data comparable to those from crosses among normal strains. Perhaps perpetual selfing is a mechanism of getting rid of deleterious combinations of genes and uncovering better combinations in homozygous state by playing genetic roulette. © 1992 Wiley‐Liss, Inc.
Mutation affecting cell separation and macronuclear resorption during conjugation in Tetrahymena thermophila: Early expression of the zygotic genotype
Authors: Kaczanowski Andrzej 
Published: May 2005

AbstractA new recessive conjugation lethal mutation was found in Tetrahymena thermophila which was named mra for macronuclear resorption arrest. Other events affected by the mra mutations are separation of pairs, DNA replication in the macronuclear anlagen, and resorption of one of the two micronuclei. In wild‐type crosses 50% of the pairs had separated by 12 hr after mixing two mating types and had completed resorption of the old macronucleus 1–2 hr later. In contrast most mra conjugants did not separate even by 24 hr after mixing and the old relic (condensed) macronucleus was seen in over 90% of them.After addition of 10mM calcium to the conjugation medium, the mra conjugants did separate but they still failed to complete resorption of the old macronucleus and to replicate macronuclear anlagen DNA in the exconjugants. The calcium induced separation of the mra conjugants occurred later than the separation of control pairs.During normal conjugation cell separation occurs before the first expression of known macronuclear genes and prior to processing of the macro‐nuclear DNA. Therefore, the mra phenotype infers that separation of conjugants requires a signal which is produced by the macronuclear anlagen at an unusually early time. © 1992 Wiley‐Liss, Inc.
A micronucleus‐limited sequence family in Tetrahymena thermophila: Organization and sequence conservation
Authors: Tsao Nora N‐G , Tsao Smiley G‐S , Pearlman Ronald E. 
Published: May 2005

AbstractDuring mocronuclear development in the ciliated protozoan Tetrahymena thermophila, sequence reorganization including sequence loss occurs. Addressing questions about the organization and nucleotide sequence of micronucleus limited regions can lead to insights about mechanisms of DNA rearrangements during macronuclear development as well as mechanisms for the maintenance of the stability of micronucleus‐limited sequence families. We have previously identified a moderately repetitive micronu‐cleus‐limited sequence family called X‐H (family members hybridize to an approximately 450 bp Xbal‐HindIII restriction fragment), completely absent from macronuclear DNA. The first member of this family which we isolated is associated with terminal sequences characteristic of a Tel‐1 element, a putative micronuclear transposable element. Two additional family members have been isolated which are not closely associated with Tel‐1 terminal sequences. We have nucleotide sequence data for three cloned members of the X‐H family. This analysis has demonstrated that the longest cloned members of the X‐H family share a region of homology of approximately 2,400 bp and are highly conserved, differing only by small insertions or deletions of 100 bp or less. The sequences from one of the sequenced family members flanking the region of homology are themselves mostly micronucleus‐limited. © 1992 Wiley‐Liss, Inc.
Tetrahymena Telomerase RNA levels increase during macronuclear development
Authors: Avilion Ariel A. , Harrington Lea A. , Greider Carol W. 
Published: May 2005

AbstractTelomeres, the G‐rich sequences found at the ends of eukaryotic chromosomes, ensure chromosome stability and prevent sequence loss from chromosome ends during DNA replication. During macronuclear development in Tetrahymena, the chromosomes fragment into pieces ranging from 20 kb to 1,500 kb. Tetrahymena telomerase, a ribonucleoprotein, adds telomeric (TTGGGG)n repeats onto telomeres and onto the newly generated macronuclear DNA ends. We have investigated whether telomerase RNA levels increase during macronuclear development, since such an increase might be expected during chromosomal fragmentation. The steady‐state level of the telomerase RNA component was used to estimate the abundance of telomerase present in mating and nonmating Tetrahymena. Northern blot analysis revealed that in vegetatively growing Tetrahymena, there were 18,000–40,000 copies of telomerase RNA per cell. In mating cultures, the levels of RNA increased 2‐to 5‐fold at 9–15 h, and 1.5‐ to 3.5‐fold in starved nonmating cultures. This increase in telomerase RNA paralleled telomerase activity, which also increased slightly in mating and starved nonmating cells. © 1992 Wiley‐Liss, Inc.
Stochastic developmental variation in the ratio of allelic rDNAs among newly differentiated, heterozygous macronuclei of Tetrahymena thermophila
Authors: Orias Eduardo , Bradshaw Amy D. 
Published: May 2005

AbstractCiliates possess nuclear dimorphism, i.e., they carry two structurally and functionally differentiated types of nuclei. The micronucleus and macronucleus serve as the germline and somatic nuclei, respectively, of the cell. The macronucleus differentiates from a mitotic sister of the micronucleus once per life cycle. Macronuclear differentiation is accompanied by a developmentally programmed set of DNA rearrangements, including chromosome fragmentation, telomere addition, and amplification. Given the diploidy of the MAC anlage, are both homologous copies of a chromosome processed and amplified equally and simultaneously in an individual differentiating MAC? We have approached this question for the case of the rDNA, exploiting previously identified DNA polymorphisms and the sensitivity of PCR. We determined allelic ratios in individual caryonide cells, i.e., the cells carrying the primary products of MAC differentiation, prior to the first division of the newly differentiated MAC. We observed stochastic variability in allelic ratios among caryonides that start with genetically identical heterozygous MACs. Either rDNA type can be in the majority. Appropriate controls make it unlikely that the ratios observed were significantly affected by variation in the assay itself. The variability may well result from the statistical variation associated with the relative timing of individual biochemical events initiating the processing and/or amplification of a few rDNA precursor molecules, presumably 4–8 at the most, in a MAC anlage. In addition to this stochastic variability, we observed a small but distinct bias in favor of the C3 rDNA. Thus the replication advantage of C3 relative to B rDNA in heterozygous MACs, previously detected during vegetative multiplication, may begin to be expressed during developmental amplification. We discuss the relevance of this stochastic developmental variability to classical genetic observations of Nanney and their collaborators on other T. thermophila loci. © 1992 Wiley‐Liss, Inc.
Bacteriophage λ DNA fragments replicate in the Paramecium macronucleus: Absence of active copy number control
Authors: Sookkim Chung , Preer John R. , Polisky Brry 
Published: May 2005

AbstractWe show that bacteriophage λ DNA fragments microinjected into the macronucleus of the ciliated protozoan Paramecium can replicate as unit‐length linear molecules. These linear DNA molecules are substrates for the addition of Paramecium telomeres by an endogenous telomerase. The linear DNA pieces can exist at copy numbers much higher than that of typical endogenous macronuclear chromosomes. We show that the copy number of injected DNA many fissions after microinjection reflects that of the original input copy number, suggesting that active control of copy number does not occur. Instead, the results suggest that injected DNA is replicated once per cell division. © 1992 Wiley‐Liss, Inc.
DNA elimination and its relation to quantities in the macronucleus of Tetrahymena
Authors: Bodenbender J. , Prohaska A. , Jauker F. , Hipke H. , Cleffmann G. 
Published: May 2005

AbstractThe macronucleus of Tetrahymena contains a large number of DNA molecules of subchromosomal size. They belong to about 270 species each one occurring at an average number of 45 copies Macronuclei divide unequally and nothing is known of segregation control. This and the elimination and degradation of DNA during macronuclear amitosis make the clonal stability of macronuclei a problem of qualitative and quantitative control on a subchromosomal level.We studied the contribution of DNA elimination to the quantitative composition of the macronucleus cytophotometrically in single cells of different strains. This was done under standard conditions and under conditions known to influence the amount of macronuclear DNA. The following results were found: Elimination of DNA occurs at almost every division. The size of the elimination body is highly variable but still positively correlated with the macronuclear DNA content. In T. thermophila the amount of eliminated DNA is 2.5% of the G2 content and is not dependent on the growth state. It varies with species, amounting to as much as 8% in T pigmentosa. During conditions which increase the macronuclear DNA content, very little DNA is eliminate. On the other hand, large amounts are eliminated under other conditions causing the macronuclear DNA content to decrease. DNA to be eliminated at division is synthesized at the same time as bulk DNA.We developed a computer program which helps us study the effects of DNA elimination and unequal divisions upon the copy numbers of subchromosomal DNA classes.The result indicates that in a given cell line at least one of the DNA molecules becoms extinct after 60 generations which we expect would cause the cell's extinction and restrict a clone's life to 60 generations. As this does not happen in nature, there must be some control of the copy numbers preventing their extinction during vegetative multiplication. Whether elimination increases or decreases the imbalance of genes remains to be investigated. © 1992 Wiley‐Liss, Inc.
Variable copy number of macronuclear DNA molecules in Tetrahymena
Authors: Brunk Clifford F. , Navas Patrick A. 
Published: May 2005

AbstractIn Tetrahymena, the DNA of the macronucleus exists as very large (100 to 4,000‐kb) linear molecules that are randomly partitioned to the daughter cells during cell division. This genetic system leads directly to an assortment of alleles such that all loci become homozygous during vegetative growth. Apparently, there is a copy number control mechanism operative that adjusts the number of each macronuclear DNA molecule so that macronuclear DNA molecules (with their loci) are not lost and aneuploid death is a rare event. In comparing Southern analyses of the DNA from various species of Tetrahymena using histone H4 genes as a probe, we find different band intensities in many species. These differences in band intensities primarily reflect differences in the copy number of macronuclear DNA molecules. The variation in copy number of macronuclear DNA molecules in some species is greater than an order of magnitude. These observations are consistent with a developmental control mechanism that operates by increasing the macronuclear copy number of specific DNA molecules (and the genes located on these molecules) to provide the relatively high gene copy number required for highly expressed proteins. © 1992 Wiley‐Liss, Inc.
Rate of phenotypic assortment in Tetrahymena thermophila
Authors: Doerder F. P. , Deak J. C. , Lief J. H. 
Published: May 2005

AbstractDuring vegetative, asexual reproduction in heterozygous Tetrahymena thermophila, the macronucleus divides amitotically to produce clonal lineages that express either one or the other allele but not both. Because such phenotypic assortment has been described for every locus studied, its mechanism has important implications concerning the development and structure of the macronucleus. The primary tools to study assortment are Rf/ the rate at which subclones come to express a single allele stably, and the output ratio, the ratio of assortee classes. Because Rf is related to the number of assorting units, a constant Rf for all loci suggests that all genes are maintained at the same copy number. Output ratios reflect the input ratio of assorting units, with a 1:1 output ratio implying equal numbers of alleles at the end of macronuclear development. Because different outcomes would suggest a different macronuclear structure, it is crucial that these parameters be accurately measured. Although published Rf values are similar for all loci measured, there has been no commonly accepted form of presentation and analysis. Here we examine the experimental determination of Rf. First, we use computer simulation to describe how the variability inherent in the assortment process affects experimental determination of Rf. Second, we describe a simple method of plotting assortment data that permits the uniform calculation of Rf, and we describe how to measure Rf accurately in instances when it is possible to score only the recessive allele. Using this method to produce truly comparable Rfs for all published data, we find that most, if not all, loci assort at Rfs consistent with ∼45 assorting units, as has been asserted. © 1992 Wiley‐Liss, Inc.
Genetic characterization of the secretory mutant MS‐1 of Tetrahymena thermophila: Vacuolarization and block in secretion of lysosomal hydrolases are caused by a single gene mutation
Authors: Hünseler Peter , Tiedtke Arno 
Published: May 2005

AbstractThe genetics and phenotypic features (light and electron microscopy) of a secretory mutant, MS‐1, of Tetrahymena thermophila blocked in secretion of lysosomal acid hydrolases have been analyzed. Although blocked constitu‐tively in secretion, MS‐1 contains active lysosomal hydrolases in amounts equivalent to the wild type. The 3:1 segregation in F‐2 in sib crosses and the 1:1 segregation in test crosses indicate that the block in secretion of lysosomal hydrolases is controlled by a recessive single gene locus termed sec. The sec allele of MS‐1 proved also to be responsible for the highly vacuolarized phenotype the mutant developed when it was transferred from nutrient medium into buffers of low ionic strength. Deletion mapping by crossing MS‐1 with nullisomic strains, all secreting lysosomal hydrolases at wild‐type rates, was performed. The sec phenotype was expressed in monosomic‐4 progeny only, indicating that the sec allele is located on chromosome 4 of T. thermophila. © 1992 Wiley‐Liss, Inc.
Ultrastructure and cell size‐dependent regulation of the adoral zone of membranelles in the heterotrich ciliate Stentor coeruleus
Authors: Jacobson Patrice M. , Lynn Denis H. 
Published: May 2005

AbstractThe number and length of oral membranelles were determined for both large and small Stentor from well‐fed, growing cultures and nutrient‐deprived cultures, respectively. Small cells possess both significantly fewer and shorter membranelles than do large cells. For both large and small cells, each membranelle is composed of three rows of basal bodies. The membranelles closest to the gullet have a third row that is only slightly shorter than the other two. The third row becomes rapidly shorter as membranelles become increasingly distant from the gullet. A short distance from the gullet, and for the remainder of the band, the third row is composed ofonly one to four basal bodies. The first two rows consist of approximately 35 basal bodies each in large cells and approximately 26 basal bodies each in small cells. This indicates that Stentor regulates the number of basal bodies per row, but not the number of rows, in response to changes in cell size. © 1992 Wiley‐Liss, Inc.
Timing of formation of Tetrahymena contractile ring microfilaments investigated by inhibition with skeletal muscle actin
Authors: Ohba Hiroyoshi , Hirono Masafumi , Edamatsu Masaki , Watanabe Yoshio 
Published: May 2005

AbstractUnderstanding the mechanism that determines the cell division plane is one of the most important problems in the fields of cell and developmental biology. Studying the timing and site of formation of contractile ring (CR) micro‐filaments provides key information for solving the problem. We tried to create a nonfunctional CR in Tetrahymena by microinjecting rabbit skeletal muscle actin, which can copolymerize with Tetrahymena actin but has properties different from those of Tetrahymena actin. When skeletal muscle actin was injected in a predivision stage, before the onset of furrow constriction, long‐term arrest of cell division was observed. Muscle actin did not cause any delay in cell division when the actin was injected at any stage other than the predivision stage. In all cases, muscle actin had little affect on other actin‐related functions. Injected skeletal muscle actin polymerized near the equatorial division plane in cases of cell division arrest; it polymerized at other nonspecific locations when cell division was observed. Arrest occurred when the microinjection took place in the 17‐min period just before the start of furrowing. This period coincides with the occurrence of equatorial deposits of p85, which is also suggested to be required for the determination of the division plane. The present experimental results are consistent with the idea that p85 is a crucial factor for determining the cell division plane and also functions as a polymerization nucleus for CR microfilaments. © 1992 Wiley‐Liss, Inc.
The influence of fission line expression on the number and positioning of oral primordia in the cdaA1 mutant of Tetrahymena thermophila
Authors: Kaczanowska J. , Buzanska L. , Frontczak M. 
Published: May 2005

AbstractDuring cytokinesis, furrowing creates new boundaries for daughter cells. Following a shift to a restrictive temperature, cells of the temperature‐sensitive cell‐division‐arrest (cdaA1) mutant of Tetrahymena thermophila complete development of the oral apparatus for the prospective posterior daughter cell before becoming arrested in cytokinesis. When maintained under weak restrictive conditions (35°C), some of the chains were arrested prior to the start of fission line formation (D‐shaped chains), whereas others manifested rudimentary unilateral furrowing on the ventral side (B‐shaped chains). In their second cell cycle following the temperature shift, the D‐shaped chains usually formed only one oral primordium, at a position highly correlated with the length of the entire chain. The B‐shaped chains always produced two separate oral primordia, located at irregular positions anterior and posterior to the division furrow, often close to the posterior oral apparatus produced during the first cycle. These results suggest that the formation of the fission line sets a reference boundary to assess the number of oral primordia and influence their position, that appear during subsequent morphogenetic episodes. They also indicate that, during cell division cycles, pre‐existing oral apparatuses do not strongly inhibit the formation of new oral apparatuses in their close vicinity. © 1992 Wiley‐Liss, Inc.
Nuclear functions in postconjugational development of Paramecium caudatum: Ability to form food vacuoles analyzed by nuclear elimination and implantation
Authors: Mikami Kazuyuki 
Published: May 2005

AbstractParamecium caudatum loses the ability to form food vacuoles at the crescent stage of the micronucleus from 5 to 6 hr after the initiation of conjugation and regains it immediately after the third division of the zygotic nucleus. To assess the micronuclear function in the development of the oral apparatus after coniugation, prezygotic micronuclei was removed from cells at various stages of conjugation, and their ability to form food vacuoles were examined. (1) When all of the prezygotic micronuclear derivatives were eliminated before the stage of formation of the zygotic nucleus, the exconjugant did not regain its ability. (2) When a zygotic nucleus or postzygotic nuclei were removed, in some cases the cell formed as many food vacuoles as did nonoperated cells after conjugation, while in other operated cells the number of food vacuoles was subnormal. (3) When a micronucleus from a cell at vegetative phase (G1) was transplanted into a cell of an amicronucleate mating pair at the stage between 8 and 9 hr after the initiation of conjugation, the implanted cell regained the ability to form food vacuoles. However, no cell regained the ability when the implantation was carried out within 1 hr after the separation of the mates. The results show that the micronucleus plays an indispensable role in the development of the oral apparatus at the stages of exchange of gametic nuclei and fertilization and that the micronucleus transplanted from asexual cells can fulfill this function. On the other hand, removal of the macronucleus from exconjugants showed that the maternal macronucleus also has an indispensable function in regaining the ability to form food Vacuoles. © 1992 Wiley‐Liss, Inc.
Timing of micronuclear mitosis and its relation to commitment to division inParamecium tetraurelia
Authors: Adl Sina M. , Berger James D. 
Published: May 2005

AbstractThis study examines the timing of micronuclear mitosis during the vegetative cell cycle and shows that mitosis begins early in the division process and coincides approximately with the earliest stages of oral morphogenesis (about 0.6 in the cell cycle in synchronous cell samples). The cc1 mutation blocks cell cycle progression prior to the point of commitment to division. Although the cc1 mutation blocks macronuclear DNA synthesis under restrictive conditions, it does not block micronuclear DNA synthesis. However, absence of functional cc1 gene product leads to blockage of micronuclear mitosis prior to completion of anaphase. This point coincides with commitment to division and is also the point at which oral morphogenesis is blocked in cc1 cells. The tim‐ings of the transition points for micronuclear mitosis and oral morphogenesis in cc1 cells are closely associated in both synchronous cell samples and in asynchronous cultures. © 1992 Wiley‐Liss, Inc.