Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Macronucleus”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10Linked to original sources
PubMed2006

Alteration of developmental program in Paramecium by treatment with trichostatin a: a possible involvement of histone modification.

In the ciliate Paramecium caudatum, the somatic macronucleus for the next generation differentiates from a zygotic germinal micronucleus during conjugation. Subsequently, progeny are programmed to enter a sexually "immature" period, during which cells do not mate. This programming occurs at a critical period during the fifth cell cycle after conjugation. Here, we show that treatment with trichostatin A, a histone deacetylase inhibitor, leads to a partial recovery of mating reactivity in immature cells, suggesting that histone acetylation can affect the developmental program. In addition, immunostaining demonstrated that Lys 4 methylation of histone H3 was absent from or present at an undetectable level in the nascent macronucleus during the first cell cycle after conjugation. The methylation level gradually increased in proportion to de novo DNA synthesis, until the new macronucleus reached the maximum level of methylation, concomitant with its full maturation. A link between gene expression and Lys 4 methylation is indirectly supported by the observation that a transcriptionally active gene was enriched by chromatin immunoprecipitation with an antibody directed against methyl-Lys 4 H3, whereas a silent gene was not. These results provide evidence that histone modification plays a key role in the regulation of gene expression and the developmental programming that determine sexual immaturity after conjugation.

Amino Acid Sequence↗
PubMed2003

Spatiotemporal sites of DNA replication in macro- and micronuclei of the ciliate Paramecium caudatum.

Spatiotemporal sites of DNA replication in macro- and micronuclei of the ciliated protozoan Paramecium caudatum were analyzed by confocal laser scanning microscopy following incorporation of the thymidine analogue BrdU and indirect immunofluorescence. In the macronucleus, replication sites were localized to numerous small domains and scattered throughout the nucleoplasm. This pattern persisted during all periods of the S phase. A single constant pattern with discrete replication foci was also observed in the micronucleus. No obvious differences were seen between the two kinds of nuclei. Pulse-chase-pulse double-labeling experiments with two thymidine analogues (CldU and IdU) revealed that dispersed sites of replication were activated at different times during the S phase and a replication site takes about 2h to complete replication in the macronucleus. When cells were labeled by BrUTP to examine transcriptional activity in the two kinds of nuclei, incorporation of BrUTP into the macronucleus occurred throughout the cell cycle, whereas there was no detectable RNA synthesis in the micronucleus. From these findings, we conclude that, despite large differences in structure and function of macro- and micronuclear genomes, both nuclei show a similar replication pattern with discrete subnuclear foci scattered throughout the nucleoplasm at all times during the S phase.

Animals↗
PubMed2005

[Epigenetics: Paramecium as a model system].

Since the middle of the last century, Paramecium has appeared as an intriguing genetic model, displaying a variety of heritable characters which do not follow the Mendel laws but are cytoplasmically inherited. The analysis of the hereditary mechanisms at play in this eukaryotic unicellular organism has provided new insight into epigenetics mechanisms. Interestingly, the revealing phenomena concern two pecularities of Paramecium, its highly elaborate surface structure (with thousands of ciliary basal bodies as cytoskeleton organizers), and its nuclear dualism (coexistence of a diploid "germline" micronucleus and a highly polyploid somatic macronucleus devoted to transcription, which contains a rearranged version of the germline genome). Analysis of variant cortical organization has led to the concept of structural inheritance, implying that assembly of new organelles and supramolecular protein complexes is guided by pre-existing organization. Analysis of other cytoplasmically inherited characters revealed that the developing macronucleus is epigenetically programmed by the maternal macronucleus through RNA-mediated, homology-dependent effects, suggesting the transcriptome should be recognized as a third actor in cellular inheritance, along with the "structurome" and the genome.

Animals↗
PubMed1988

Molecular evidence for somatic recombination in the ribosomal DNA of Tetrahymena thermophila.

The ribosomal DNA (rDNA) in Tetrahymena thermophila is a 21-kilobase-pair palindromic DNA molecule that replicates autonomously in the macronucleus and is maintained at the level of about 10,000 copies per macronucleus. The rDNA of inbred strain C3 outreplicates the rDNA of inbred strain B in most B/C3 heterozygous macronuclei, generating macronuclei containing exclusively C3 rDNA sequences. In 1% or less of the B/C3 heterozygous macronuclei, however, rDNA sequences derived from both B and C3 strains persist in the macronucleus (co-maintainers). We report here that long-term culture of co-maintainers has yielded recombinant rDNA molecules combining sequences from both parental inbred strains. The genetic structure of such molecules also gives us virtual certainty that the differential replication of C3 rDNA with respect to B rDNA is due to the DNA sequence difference previously reported in domain 2 of the rDNA replication regions of the two strains.

Animals↗
PubMed2002

Coding properties of macronuclear DNA molecules in Sterkiella nova (Oxytricha nova).

The DNA in the macronucleus of the stichotrichs like Sterkiella nova (formerly Oxytricha nova) occurs in short molecules ranging from approximately 200 bp to approximately 20,000 bp. It has been estimated that there are approximately 24,500 different sized DNA molecules in the macronucleus. Single genes have been assigned to approximately 130 different sized macronuclear molecules in various stichotrichs (12 in Sterkiella nova) and hypotrichs, suggesting that each of the -24,500 different sized molecules encodes a different gene. To test this proposition we sequenced 31 macronuclear molecules picked randomly from a plasmid library of macronuclear DNA and analyzed them for potential gene content. The open reading frames (ORFs) in three short molecules encode amino acid (aa) sequences that do not match sequences in GenBank. They may or may not encode genes. Twenty-eight of the 31 molecules contain ORFs encoding aa sequences with significant matches to sequences in GenBank. Six molecules contain more than one ORF with a significant match to GenBank. These results indicate that almost all, if not all of the -24,500 different molecules encode one or more genes, yielding an estimate of -26,800 genes in the macronucleus of S. nova.

Animals↗
PubMed1966

The syntheses of total macronuclear protein, histone, and DNA during the cell cycle in Euplotes eurystomus.

The syntheses of histone, total protein, and DNA during the cell cycle were measured in the macronucleus of Euplotes eurystomus by assaying the incorporation of tritiated amino acids and tritiated thymidine in groups of 800 to 1000 synchronized cells. The synthesis of DNA begins at 30% completion of the cell cycle, proceeds at a constant rate, and ends very shortly before the beginning of macronuclear division. Histone labeling is absent during G(1), begins in phase with DNA synthesis, continues at an unchanging rate during the S phase, and ends with the completion of DNA synthesis. The results support the view that the syntheses of histone and DNA are closely coupled events. Label in total protein accumulates at a constant rate during G(1) and appears to shift to a slightly higher rate when histone synthesis begins. At division, radioactive DNA, histone, and total protein are distributed equally between the daughter macronuclei without loss of radioactivity. Radioautographic analysis showed that protein labeling occurs throughout the macronucleus during the entire life cycle. There was no clear difference in the degree of protein labeling between replicated and unreplicated regions of the macronucleus. The distribution of label suggests that most of macronuclear protein labeling during the cell cycle is concerned with the events of transcription rather than replication.

Amino Acids↗
PubMed1981

Tandemly repeated C-C-C-C-A-A hexanucleotide of Tetrahymena rDNA is present elsewhere in the genome and may be related to the alteration of the somatic genome.

The ribosomal RNA genes of the Tetrahymena macronucleus exist as extrachromosomal, linear molecules. The termini of these molecules have been shown to contain the tandemly repeated hexanucleotide (C-C-C-C-A-A)n. In this study the same or related sequences were found in other locations of the genome. Using the depurination method, we showed that macronuclear DNA contained this sequence even after rDNA had been removed. The sequence was found mainly in the repetitive fraction of the DNA. The presence of this sequence in both the macronucleus and the micronucleus was also shown by Southern hybridization using C-C-C-C-A-A repeat as a probe. Comparison between the hybridization patterns of macronuclei and micronuclei reveals interesting differences. Whereas the two nuclei share the same genetic origin, the majority of the restriction enzyme digestion sites flanking the C-C-C-C-A-A repeat appear to be different. Such a difference was found to be specific for this sequence, because it was not detected when other sequences were used for hybridization. These results suggest that some kind of alteration has occurred in the genome during the formation of the macronucleus, and that the C-C-C-C-A-A repeat may be related to this process.

Animals↗
PubMed1987

Genomic organization and developmental fate of adjacent repeated sequences in a foldback DNA clone of Tetrahymena thermophila.

DNA sequence elimination and rearrangement occurs during the development of somatic cell lineages of eukaryotes and was first discovered over a century ago. However, the significance and mechanism of chromatin elimination are not understood. DNA elimination also occurs during the development of the somatic macronucleus from the germinal micronucleus in unicellular ciliated protozoa such as Tetrahymena thermophila. In this study foldback DNA from the micronucleus was used as a probe to isolate ten clones. All of those tested (4/4) contained sequences that were repetitive in the micronucleus and rearranged in the macronucleus. The presence of inverted repeated sequences was clearly demonstrated in one of them by electron microscopy. DNA sequence analysis showed that the left portion of this clone contains three tandem, directly repeated copies of a 340-bp sequence, a 120-bp portion of which appears in inverted orientation at a 1.6-kb distance. This clone, pTtFB1, was subjected to a detailed analysis of its developmental fate. Subregions were subcloned and used as probes against Southern blots of micronuclear and macronuclear DNA. We found that all subregions defined repeated sequence families in the micronuclear genome. A minimum of four different families was defined, two of which are retained in the macronucleus and two of which are completely eliminated. The inverted repeat family is retained with little rearrangement. Two of the families, defined by subregions that do not contain parts of the inverted repeat, one in the "loop" and one in the "right flanking region," are totally eliminated during macronuclear development--and contain open reading frames. A fourth family occurs in the "loop" region and is rearranged extensively during development. The two gene families that are eliminated are stable in the micronuclear genome but are not clustered together as evidenced by experiments in which DNAs from nullisomic strains are used to map family members to specific micronuclear chromosomes. The inverted repeat family is also stable in the micronuclear genome and is dispersed among several chromosomes. The significance of retained inverted repeats to the process of elimination is discussed.

Animals↗
PubMed1994

The role of macronuclear DNA sequences in the permanent rescue of a non-mendelian mutation in Paramecium tetraurelia.

The paramecium tetraurelia mutant called d48 has a complete copy of the A surface protein gene in its micronuclei, but lacks the A gene in the macronucleus. Previous experiments have shown that microinjection of a plasmid containing the entire A gene or a large portion of the gene into the macronucleus of d48 rescued the cell line after formation of a new macronucleus (autogamy). Here we show that several different regions of the A gene can rescue d48, but 100% of the activity cannot be localized to a single, defined region. Inversion of a sequence contained within an A gene plasmid had no measurable effect on rescue efficiency and co-injection of two different plasmids results in enhancement of rescue activity despite the non-contiguous form of the DNA sequences. Both these results suggest that no specific product (RNA or protein) with defined end points is made from the rescuing fragment. A unique restriction site was created in the A gene and used to demonstrate that the injected DNA does not serve as a direct template for the synthesis of the new macronuclear DNA. Models to explain the action of the injected DNA are discussed.

Animals↗
PubMed1996

A Mendelian mutation affecting mating-type determination also affects developmental genomic rearrangements in Paramecium tetraurelia.

In Paramecium tetraurelia, mating type is determined during the differentiation of the somatic macronucleus from a zygotic nucleus genetically competent for both types, O and E. Determination of the developing macronucleus is controlled by the parental macronucleus through an unknown mechanism resulting in the maternal inheritance of mating types. The pleiotropic mutation mtFE affects macronuclear differentiation. Determination for E is constitutive in mutant homozygotes; a number of unrelated mutant characters are also acquired during development. We have examined the possibility that the mutation causes a defect in the developmental rearrangements of the germ-line genome. We show that the excision of an IES (internal eliminated sequence) interrupting the coding sequence of a surface antigen gene is impaired in the mutant, resulting in an alternative macronuclear version of the gene. Once established, the excision defect is indefinitely transmitted across sexual generations in the cytoplasmic lineage, even in a wild-type genetic context. Thus, the processes of mating-type determination and excision of this IES, in addition to their common sensitivity to the mtFE mutation, show a similar maternal inheritance of developmental alternatives in wild-type cells, suggesting a molecular model for mating-type determination.

Animals↗
PubMed2000

Tetrahymena macronuclear genome mapping: colinearity Of macronuclear coassortment groups and the micronuclear map on chromosome 1l.

The genetics of the ciliate Tetrahymena thermophila are richer than for most other eukaryotic cells, because Tetrahymena possesses two genomes: a germline (micronuclear) genome that follows a Mendelian model of genetic transmission and a somatic (macronuclear) genome, derived from the micronuclear genome by fragmentation, which follows a different genetic transmission model called phenotypic assortment. While genetic markers in the micronucleus fall into classical linkage groups under meiotic recombination and segregation, the same markers in the macronucleus fall into coassortment groups (CAGs) under phenotypic assortment by the random distribution of MAC chromosome pieces. We set out to determine whether genomic mapping in the macronucleus by genetic means is feasible. To investigate the relationship between the micronuclear map and coassortment groups, we systematically placed into CAGs all of the markers lying on chromosome 1L that are also found in the macronucleus. Sixteen CAGs were identified, 7 of which contain at least two loci. We have concluded that CAGs represent a fundamental genetic feature of the MAC. The MIC and MAC maps on 1L are colinear; that is, CAGs consist exclusively of markers that map to a continuous segment in a given region of the micronuclear map, with no intervening markers from other CAGs. These findings provide a solid foundation for exploiting the MAC chromosome pieces to build a physical map of the Tetrahymena genome.

Animals↗
PubMed2001

Widespread distribution of extensive chromosomal fragmentation in ciliates.

Ciliates are a diverse group of eukaryotes characterized by their division of nuclear function into a "germ line" micronucleus and a "somatic" macronucleus. After conjugation, chromosomes in the transcriptionally active macronucleus develop by fragmentation, elimination, and amplification of germ line chromosomes. Extensive chromosomal processing that generates a macronucleus with gene-sized fragments has thus far been well documented in members of only one class of ciliates, the Spirotrichea. Here we establish the broad distribution of extensive fragmentation among members of the class Phyllopharyngea and the genera Metopus (order Armophorida) and Nyctotherus (order Clevelandellida). Moreover, analyses of small-subunit rDNA genealogies indicate that gene-sized chromosomes occur in members of the three separate clades: (1) the class Spirotrichea, (2) the class Phyllopharyngea, and (3) the two orders Clevelandellida and Armophorida. Together, these data indicate that the generation of gene-sized chromosomes is widespread and demonstrate multiple origins of extensive fragmentation within ciliates.

Animals↗
PubMed1989

Precise excision of telomere-bearing transposons during Oxytricha fallax macronuclear development.

In ciliated protozoa, development of the macronucleus from a copy of the germ line micronucleus involves elimination of a large number of sequences by DNA splicing akin to precise excision of transposons. The known examples of such internal eliminated sequences (IESs) are not repetitive. The telomere-bearing elements (TBE1s) of Oxytricha fallax are a family of transposons. We show that two particular TBE1s are also IESs. TBE1-1 and TBE1-2 disrupt a micronuclear region that codes for macronuclear DNA. A variety of tests indicates that each TBE1 and one copy of the flanking target repeat is absent from most, if not all, molecules of the macronuclear DNA, as if the TBE1s were precisely excised during macronuclear development. Three alternative explanations for the absence of TBE1-1 and TBE1-2 from the macronuclear DNA were tested. First, because two other highly homologous versions of that DNA are also found in the macronucleus, recombination between versions during or after macronuclear development could have bypassed the elements. Recombination in the regions flanking the elements was not detected. Second, micronuclear DNA blots show no evidence of a micronuclear counterpart of the macronuclear region that lacks TBE1-1. Third, TBE1-2 was demonstrated in two sexually independent cell lines. This shows that it pre-existed in the germ line, as opposed to having transposed into the micronuclear DNA subsequent to the generation of the macronucleus of the vegetative line that is usually studied. We conclude that TBE1-1 and TBE1-2, and possibly many of the other approximately 1900 micronucleus-limited TBE1s are excised as IESs during macronuclear development. These transposons appear to enjoy the luxury of relaxed constraints on family expansion, because they are removed from the genome before it is expressed. We discuss the possibility that all IESs are transposon-derived, that all are excised by transposition machinery, and that linear excision products are early intermediates in transposition.

Animals↗
PubMed1976

RNA synthesis in division synchronized Tetrahymena: macronuclear and cytoplasmic RNA.

Synthesis of RNA in the macronucleus and appearance of RNA in the cytoplasm were studied in heat synchronized Tetrahymena pyriformis GL and compared to those found under conditions of logarithmic growth (28 C) and during heat shocks (34 C). In macronuclei of logarithmically growing cells precursors were processed to 2 rRNA species (25S and 17S). In addition, another RNA (15S), more homogeneous than the RNA (8-15S) in the cytoplasm, was observed in the macronucleus. Both 17S and 25S rRNA species were found in the cytoplasm, 17S rRNA appearing more rapidly than 25S rRNA. Synthesis of rRNA was suppressed at 34 C in cells subjected to heat synchronization; 8-15S RNA synthesis appeared to be inhibited to a lesser extent. During the time preceding the first synchronized division, the synthesis of rRNAs in the macronucleus slowly recovered. Early in the cycle, almost no newly synthesized rRNAs were extracted. By 30 min after the last heat shock (EH), most of the RNA synthesized was not identified as rRNA. By 60 min after EH, the pattern of RNA synthesis had not returned to that observed in logarithmically growing cells.

Animals↗
PubMed1977

Qualitative and quantitative studies on DNA and RNA synthesis in Loxodes striatus nuclei.

In this study the characteristics of the synthesis of DNA and RNA in the nuclei of Loxodes were investigated. Loxodes striatus is a primitive ciliate with 2 pairs of structurally differentiated diploid nuclei, the macro- and micronuclei. The macronuclei and differentiated morphologically into a clearly recoginzable central core and an outer zone. To determine DNA and RNA synthesis, individual organisms were analyzed by autoradiography after incubating groups of cells with a 3H-labeled precursor ([3H]thymidine for DNA and [3H]uridine for RNA). The following observations were made: (A) All portions of macro- and micronuclei appeared to contain DNA as judged by the localizations of incorporated [3H]thymidine. (B) The macro- and micronuclei did not synthesize DNA at the same time; moreover, the duration of DNA synthesis in the former was much longer than of the latter nucleus. (C) Replication of DNA in the inner core and outer zone of the macronucleus occurred at separate times with little if any overlap. (D) All of the detectable [3H]uridine incorporation was found in the macronucleus and none in the micronucleus. Within the macronucleus the central core was more heavily labeled. (E) The quantitative differences in the label of the different components synthesis can occur in adult macronuclei. The possible explantion of these results is discussed in the context of the nuclear evolution of ciliates and of recent information on nuclear differentiation.

Animals↗
PubMedDate not supplied

Monoclonal antibody to a bacterial endonuclear symbiont Holospora cross reacts with proteins of contractile vacuole radial canals of Paramecium species.

A monoclonal antibody (mAb) IR-2-1 was raised against a 67-kDa protein purified from the macronucleus-specific bacterial symbiont Holospora obtusa of Paramecium caudatum. The mAb was found to react with two bands (31 and 67-kDa) on gels of H. obtusa. Indirect immunofluorescence microscopy showed that these antigens were distributed inside the cells. However, unexpectedly, this mAb also cross reacted with the radial arms of the contractile vacuole in P. caudatum, P. tetraurelia, P. multimicronucleatum, P. jenningsi and P. bursaria as well as with their cytoplasm. Immunoelectron microscopy showed that the antigens were located on the decorated spongiome of the radial arms. In immunoblots, mAb IR-2-1 reacted with a band of 67 kDa in all Paramecium species examined. However, no band appeared in the immunoblot of isolated macronuclei of H. obtusa-free P. caudatum and no label was seen in the nuclear matrix of the macronucleus of air-dried P. caudatum. These results suggest that the 67-kDa antigen found in H. obtusa was not imported from the host macronucleus and the same antigen in the host contractile vacuoles and cytoplasm were not derived from the symbiont. These results also showed that an epitope on the decorated spongiome of the Paramecium species is shared by its bacterial symbiont. In contrast to the decorated tubule-specific mAb, DS-1, the antigens for IR-2-1 appeared to be loosely membrane bound as they were lost in paraformaldehyde fixed and acetone permeabilized Paramecium.

Animals↗
PubMedDate not supplied

New contributions to two heterotrichous ciliates, Folliculina simplex (Dons, 1917), Condylostoma curva Burkovsky, 1970 and one licnophorid, Licnophora lyngbycola Fauré-Fremiet, 1937 (Protozoa, Ciliophora): descriptions of morphology and infraciliature.

The living morphology and infraciliature of two heterotrichous and one licnophorid ciliates from the north China seas, i.e. Folliculina simplex (Dons 1917), Condylostoma curva Burkovsky, 1970, and Licnophora lyngbycola Fauré-Fremiet, 1937, were investigated using protargol impregnation and in vivo observations. Updated diagnoses and redescriptions of each species are provided. The improved diagnosis of Folliculina simplex is as follows: blue-greyish to blue-greenish Folliculina with broad and unequal-sized peristomial lobes; adoral zone of membranelles comprises about 400 membranelles and forms two-and-half turns within buccal cavity; paroral membrane extends entire length of adoral zone of membranelles; about 50 somatic kineties in mid-body; single ovoid to ellipsoid macronucleus and several micronuclei; lorica vase-shaped, about 150-250 microm long, often with jelly-like covering and inconspicuous neck; marine habitat. Improved diagnosis for Licnophora lyngbycola: marine Licnophora with cup-shaped body and glabrous adhesive disc with which the organism attaches to the filaments of the colourless cyanobacterium Lyngbya; in vivo 80-130 microm long; about 140 adoral membranelles, one micronucleus and a single C-shaped, moniliform macronucleus consisting of about 14 nodules; two specialized dorsal kineties; five peripheral rings on adhesive disc, the 2nd, 3rd, and 5th (outermost) which are incomplete. Based on the Qingdao population, an improved diagnosis for Condylostoma curva is supplied: yellow-brownish Condylostoma with oval to elongated body shape; about 150-350 microm long in vivo; about 68-108 membranelles in adoral zone of membranelles, 4-8 frontal cirri, 22-32 somatic kineties; macronucleus moniliform with 5-13 nodules; with cortical granules; marine habitat.

Animals↗
PubMed2006

The condensin complex is essential for amitotic segregation of bulk chromosomes, but not nucleoli, in the ciliate Tetrahymena thermophila.

The macronucleus of the binucleate ciliate Tetrahymena thermophila contains fragmented and amplified chromosomes that do not have centromeres, eliminating the possibility of mitotic nuclear division. Instead, the macronucleus divides by amitosis with random segregation of these chromosomes without detectable chromatin condensation. This amitotic division provides a special opportunity for studying the roles of mitotic proteins in segregating acentric chromatin. The Smc4 protein is a core component of the condensin complex that plays a role in chromatin condensation and has also been associated with nucleolar segregation, DNA repair, and maintenance of the chromatin scaffold. Mutants of Tetrahymena SMC4 have remarkable characteristics during amitosis. They do not form microtubules inside the macronucleus as normal cells do, and there is little or no bulk DNA segregation during cell division. Nevertheless, segregation of nucleoli to daughter cells still occurs, indicating the independence of this process and bulk DNA segregation in ciliate amitosis.

Adenosine Triphosphatases↗