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Topic: Macronucleus

	Moniliform macronucleus of Stentor
		In addition to possessing cilia as a locomotory structure once in their life cycle, ciliates are characterized by having two types of nuclei, a micronucleus and macronucleus, therefore members of this protozoan group are sometimes called heterokaryotic organisms.
		The macronucleus is larger and has various shapes, from a simple round form to a dendritic one depending on the species.
		The macronucleus has major duties in regulation of any somatic or vegetative process of the organism such as nutrition, metabolism, RNA synthesis, morphogenesis, regeneration, etc. Broadly speaking, it controls any asexual mechanism occurring in the ciliate cell.
	www.microscopy-uk.org.uk /mag/artjul03/ccstentor.html (665 words)

	Jason Wolfe: Research from the WolfeLab
		The old macronucleus (OM) is condensed and is in the process of being eliminated.
		Developing macronuclei are lightly stained, as expected, testifying to DNA cleavage which occurs during normal genomic rearrangement.
		However, the old macronucleus is intensely stained, indicating massive digestion of DNA.
	www.wesleyan.edu /bio/wolfe/wolfelab.html (93 words)

	Paramecium tetraurelia
		Both the macronucleus and the micronucleus are derived from copies of the zygotic nucleus.
		The programmed development of the macronucleus includes DNA amplification by a factor of about 250, precise elimination of short internal sequences called IES and imprecise elimination of regions which are rich in transposons and repeated sequences and are probably heterochromatic.
		The majority of the heterochromatin is eliminated during development of the macronucleus, which is therefore essentially euchromatic and devoid of repeat sequences and microsatellites.
	www.genoscope.cns.fr /externe/English/Projets/Projet_FN/organisme_FN.html (1602 words)

	Tracy Morton Sonneborn, October 19, 1905—January 26, 1981 \| By John R. Preer, Jr. \| Biographical Memoirs
		Finally, studying mating type and an unusual trichocyst mutant, he uncovered the first examples of a strange non-Mendelian phenomenon in which the macronucleus of ciliated protozoa determines the cytoplasm, and the cytoplasm in turn determines newly forming macronuclei, thereby passing genetic information from the old disintegrating macronucleus to the newly forming macronuclei.
		The macronucleus divides amitotically, and the micronuclei divide by mitosis.
		In short, in the formation of new macronuclei the cytoplasm determines the macronucleus for mating type, and once the macronucleus is determined it never changes.
	www.nap.edu /html/biomems/tsonneborn.html (5921 words)

	A Simple Stain for the Nuclei of Paramecium
		Paramecium is a ciliate and shares with all members of that group a large macronucleus with many copies of each gene and a small micronucleus which is ordinarily diploid.
		The macronucleus is where most of the mRNA is produced as a result of gene action.
		She developed this simple stain to be able to see whether the macronucleus was in one large piece, which is usually is, or was fragmented into pieces.
	www.hope.edu /academic/biology/meciums/paradipp.htm (397 words)

	INABIS '98 - Origin of Cellular Lifespan: From a View of Paramecium
		In almost all ciliates, in which differentiation into the germ (diploid micronucleus) and soma (polygenic macronucleus) occurs at the nuclear level, and in which both the germ and soma are proliferative, the germ is produced from the germ and the soma from the soma during asexual reproduction.
		The generally accepted idea is that the mutations accumulated in the macronucleus are canceled by degrading it and constructing a new macronucleus from the germ micronucleus.
		It is noteworthy that the macronuclear degradation is suicidal (apoptotic), because apoptotic DNAs of ~200 bp and multiples thereof are detectable on agarose gel electrophoresis [16,17], and because macronuclear degradation is inhibited by inhibitors of gene expression such as actinomycin D and cycloheximide and by nuclease inhibitors [17,18].
	www.mcmaster.ca /inabis98/higuchi/takagi0233/two.html (3498 words)

	Clonal aging in Paramecium tetraurelia. II. Evidence of functional changes in the macronucleus with age. (Site not responding. Last check: 2007-10-31)
		The contribution of the macronucleus of Paramecium tetraurelia to the long term proliferation potential of a cell line was tested using a nuclear transplantation protocol.
		The mean life spans of uninjected donor controls and the mean total life spans of the transplanted macronuclear material (donor age at injection plus subsequent hybrid proliferation) are similar, regardless of the age of the donor at the time of transplantation.
		The results also show that the proliferation potential of the donor macronucleus does not appear to be changed to any great degree by transplantation into a host cell of different clonal age.
	www.arclab.org /medlineupdates/abstract_3553762.html (313 words)

	Differential Staining of Apoptotic Nuclei in Living Cells: Application to Macronuclear Elimination in Tetrahymena -- ...
		The precondensed macronucleus stains green; lysosomes stain red and are randomly distributed throughout the cytoplasm (C).
		In cells with condensed macronuclei (D), the macronuclear anlagen are not visible, micronuclei stain green (arrows), and the condensed macronucleus stains orange-red (arrowhead).
		The parental macronucleus has become highly condensed (cm), and two of the four micronuclei in each cell have enlarged to become macronuclear anlagen (an).
	www.jhc.org /cgi/content/full/45/5/675 (4741 words)

	Lysosomal enzymes in the macronucleus of Tetrahymena during its apoptosis-like degradation
		Of particular interest in the present study are stages k-p during which the chromatin of the old macronucleus becomes highly condensed, the condensed macronucleus moves, generally, to the posterior end of the cell, the DNA of the old macronucleus is digested, and the structure disappears.
		At this stage (comparable to Figure 1m), the macronucleus is condensed (arrow) and has moved to the posterior end of the cell.
		After macronuclear condensation, the old macronucleus is stained yellow, a combination of blue and orange, suggesting that the nucleus has become acidified (Figure 3b).
	www.nature.com /cdd/journal/v8/n3/full/4400807a.html (5711 words)

	Hot Topics! Small RNAs May Cause Genomic Rearrangements in Tetrahymena
		The polyploid macronucleus acts as the transcription center of the cell during vegetative growth.
		The old polyploid macronucleus, in the meantime, is destroyed by apoptosis (1, 2).
		The scan RNAs would subsequently be transferred from the old micronucleus to the old macronucleus (where IES elimination and chromosome breakage have already taken place)--this transfer could possibly be mediated via TWI1.
	www.ambion.com /techlib/hottopics/scnRNA_10042002.html (950 words)

	Ciliate Life Cycle
		The main issue in thinking about the ciliate life cycle is to understand that the cell is controlled by the macronucleus which is a somatic nucleus (that is, it is not involved in transmission of information across sexual generations).
		These losses may be either between macronucleus destined sequences or they may occur within a sequence destined for the macronucleus.
		Not only is a slngle gene sized molecule in the macronucleus derived from several non-contiguous micronucelar Sequences, but the order of these macronucleus destined sequences is changed during the process of macronuclear development.
	www.zoology.ubc.ca /courses/bio332/Lectures/Ciliates/ciliate_life_cycle.htm (1580 words)

	Modelling senescence in ciliates (ExploSYS)
		Asexually reproducing hypotrichous ciliates undergo senescence, which is in general attributed to degenerative processes in the macronucleus, assuming that a loss of viability is based on a loss of genetic elements.
		It is generally accepted that the genetic elements in the macronucleus of Hypotrichs segregate randomly, a process which potentially can lead to aneuploid imbalances in the distribution of gene copies.
		C: the initial pre-replication copy number is n=15,000 for all macronucleus chromosomes except for one rare chromosome with 1,000 copies (indicated by an arrow in C2).
	www.uni-tuebingen.de /modeling/Mod_Ciliates_en.html (461 words)

	Ciliates (Site not responding. Last check: 2007-10-31)
		One daughter haploid nucleus in each cell moves across the cytoplasmic bridge and fuses with the remaining daughter nucleus in the other cell forming a diploid nucleus in each cell.
		The old macronucleus disintegrates and a new one is formed from the micronucleus.
		They are new individuals and their macronucleus will soon reflect that fact.
	users.rcn.com /jkimball.ma.ultranet/BiologyPages/C/Ciliates.html (380 words)

	Separation of Micronuclear DNA of Stylonychia lemnae by Pulsed-Field Electrophoresis and Identification of a DNA ...
		in the mature macronucleus, indicating that it is eliminated during
		the linear DNA molecules of the micronucleus and the macronucleus
		Because the described results strongly suggest that the 90-kb fraction is localized in the micronucleus and not in the macronucleus
	www.genome.org /cgi/content/full/9/7/654 (4292 words)

	Conjugation
		Migratory pronuclei are exchanged through a temporary junction of the two cells; these then fuse with a stationary pronucleus to form a zygotic nucleus in each cell.
		The zygotic nucleus divides twice to form four identical nuclei, during which time the old macronucleus is degraded.
		Two of the four zygotic clones develop into "anlagen" (immature macronuclei), which undergo a wide array of genome rearrangements, including chromosome breakage, programmed DNA elimination, and telomere addition.
	www.ciliate.org /conjugation.shtml (415 words)

	Paramecium
		These single celled organisms must perform all of the same functions as a multicellular organism without the luxury of labor division amongst specialized cells, and it is their ability to fulfill these requirements along with their elaborate ultrastructure which places them among the most functionally complex cells.
		Ciliates are exceptional among the eukaryotes (nucleated cells) since they possess one macronucleus and at least one micronucleus, whereas most eukaryotes have just one DNA containing nucleus.
		The macronucleus participates in the day to day activities of growth and reproduction while the micronucleus remains relatively dormant until the cell undergoes some type of sexual process.
	www.bio.umass.edu /biology/conn.river/parameci.html (629 words)

	RedNova News - Science - The use of RNAi to analyze gene function in spirotrichous ciliates (Site not responding. Last check: 2007-10-31)
		For labelling the old vegetative macronucleus BrdU was added one day prior to conjugation and after washing the cells several times in Pringsheim medium conjugation was induced.
		To analyze whether a new abnormal macronucleus is formed in these cells or whether the observed fragments correspond to the old macronucleus its DNA was tested for IES excision and fragmentation as described (Jonsson et al.
		Macronucleus after inhibition of the [alpha]- subunit of the telomere-binding protein stained with an anti- [alpha]-telomere-binding protein antibody, d) same macronucleus as in (c) stained with DAPI.
	www.rednova.com /news/display?id=51602 (2829 words)

	title (Site not responding. Last check: 2007-10-31)
		During sexual reproduction, the micronucleus undergoes meiosis and gives rise to a new micronucleus and macronucleus while the parental macronucleus is degraded.
		During nuclear differentiation, the daughter macronucleus undergoes extensive DNA rearrangement in which 1000’s of internal eliminated sequences (IES’s) are excised.
		The presence of the homologous IES in the parental macronucleus, or its transcripts, may sequester or degrade the small RNA’s before they are able to target the IES in the developing macronucleus, leading to failure of the IES’ rearrangement and its retention in the new macronucleus.
	www.nslc.wustl.edu /research/hhmi/03fellows/Arce-Larreta.html (288 words)

	Results
		During this stage, the micronucleus is a discrete organelle in close physical contact with the macronucleus.
		A green trail can be seen between the two micronuclei; at higher brightness levels, the trail can be seen wrapping around the right micronucleus and attaching at the right side.
		Two new micronuclei have formed in what would soon become daughter cells, the macronucleus has undergone amitosis, and Cytokinesis is progressing as the cleavage furrow becomes defined.
	www.stolaf.edu /people/schneidb/Results.html (547 words)

	CELL BIOLOGY: ON TETRAHYMENA
		Macronucleus chromosomes partition randomly followed by counting and readjustment of each chromosome's copy number.
		DNA elimination occurs in the developing macronucleus, under epigenetic regulation from the parental macronucleus, which is later consumed internally.
		Comparative analyses of the macronucleus and micronucleus have yielded histone variants, a histone code of post-translational modifications and other properties of chromatin now recognized to be general features of eukaryotic biology.
	www.scienceweek.com /2005/sw050617-3.htm (1472 words)

	[No title]
		(1974) have 6 dorsal kineties and one S-shaped macronucleus.
		The micronucleus is situated close to the macronucleus on the left anterior edge of the body.
		Macronucleus containing numerous small nucleoli, characteristically T-shaped, with two shorter arms and slightly curved "stem"; shape variable, right arm generally longer than left; sometimes hook-shaped protrusion in middle of stem.
	www.nies.go.jp /chiiki1/protoz/morpho/euplotes.htm (7448 words)

	Class Heterotrichea: Stentor
		The macronucleus consists of a string of elliptical nodes held together by cytoplasmic bridges-a moniliform arrangement.
		During cytokinesis, the ovoid macronucleus becomes more elongate as microtubule bundles form outside the macronuclear envelope, the so-called extramacronuclear microtubules.
		Once the macronucleus has separated into two and the cells have also separated, the macronuclear nodes begin to form again.
	www.uoguelph.ca /~ciliates/repgenera/stentor.html (528 words)

	hybrid vigor \| the birth of death
		This may be an origin of aging in paramecia; with each generation, the macronucleus shrinks, and the effect of any mutated genes grows in proportion.
		At a certain point, the macronucleus becomes too small and scrambled to function, and the cell triggers apoptosis.
		The new macronucleus is rejuvenated both in size and in the possible compensation for bad genes by new genes from conjugation.
	www.emory.edu /COLLEGE/HYBRIDVIGOR/death.htm (1498 words)

	Intestinal Protozoa
		The large kidney-shaped macronucleus is involved in the 'housekeeping' or somatic functions of the cell, whereas the smaller spherical micronucleus contains the complete genome.
		Formation of the macronucleus involves fragmentation of the chromosomes and loss of some DNA sequences.
		The micronucleus (miN) may not always be apparent because of its close association with the macronucleus.
	www.tulane.edu /~wiser/protozoology/notes/intes.html (8610 words)

	Protist Images: Prorodon (Site not responding. Last check: 2007-10-31)
		Body ellipsoidal, ovoid or cylindrical in shape; cytostome apical, circular; cytopharynx equipped with well-developed double nematodesmata; somatic ciliation uniform, kinetosomes paired; macronucleus ovoid, reniform or ellongate; as many species descriptions are insufficient, many are indistinguishable (Carey, 1992).
		Prorodon teres Ehrenberg, 1838: Body cylindrical, caudal cilia absent; a single macronucleus; 130-200 μm long; large cytopharyngeal apparatus (Carey, 1992).
		Prorodon diaphanus Dragesco, 1960: A small transparent species, 50 μm long; cell body ovoid; kineties 22 or 24; mucocysts can be observed in the cortex; cytostome apical and quite large, equipped with trichocysts; cilia around the cytostome longer; macronucleus large; contractile vacuole terminal (Carey, 1992).
	130.158.208.53 /WWW/PDB/Images/Ciliophora/Prorodon/sp_3.html (336 words)

	The telomerase-associated protein p43 is involved in anchoring telomerase in the nucleus -- Möllenbeck et al. 116 ...
		macronucleus in spirotrichous ciliates are of homogenous length,
		in the replication machinery of the ciliate macronucleus.
		Telomeric sequences are bound to the nuclear matrix by an interaction of the telomere-binding protein (TEBP) with components of this structure.
	jcs.biologists.org /cgi/content/full/116/9/1757 (2826 words)

	Ancient defense mechanism may still be protecting us
		This macronucleus houses about 15 percent fewer DNA sequences than the smaller one, and when the cell mates to create a new generation of cells, this large macronucleus withers and dies.
		The result of this complex exchange and re-exchange of RNA strands is that the developing macronucleus now contains only the organism's DNA that was present in both the original macronucleus and the micronucleus, but not any new DNA that could have disastrous effects.
		The original macronucleus then withers away, leaving the new macronucleus and the micronucleus, both of which divide as the cell divides into identical daughter cells, each with a new set of nuclei.
	www.eurekalert.org /pub_releases/2002-10/uor-adm101702.php (819 words)

	Biological Sciences (Site not responding. Last check: 2007-10-31)
		During sexual reproduction, the macronucleus is degraded and a new one develops from a mitotic product of the micronucleus.
		To this end, we are working to characterize eliminated elements and to identify cis-acting DNA sequences required for DNA rearrangement and the proteins required for site-specific cutting and ligation of the DNA.
		Recent experiments indicate that foreign DNA sequences can be eliminated from the developing macronucleus and that the efficiency of their deletion increases with the copy number of the element.
	mendel.biol.mu.edu /faculty/karrer.html (729 words)

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