Organization of Genetic Material in the Macronucleus of Hypotrichous Ciliates

Murti, K.G.

doi:10.1007/978-1-4615-7148-3_4

Cited by 18 publications

(12 citation statements)

References 37 publications

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“…These interactions are resolved in the replication band Postberg et al, 2001). Other electron-microscopy studies showed that chromatin of the macronucleus forms rosette-like DNA-protein structures after limited proteolysis (Murti and Prescott, 2002;Prescott, 1994). When Stylonychia macronuclei are examined in spread electron microscopical preparations, long continuous chromatin fibres can be visualised (Meyer and Lipps, 1981).…”

Section: Discussionmentioning

confidence: 99%

“…The macronucleus contains numerous, mostly unstained, spherical structures with one or few delimitated spots of stained chromatin that is mostly located in the centre, or with no visible chromatin at all. These structures have been previously described as putative nucleoli (Kloetzel, 1970;Murti, 1973;Murti and Prescott, 2002) (Fig. 1b, inset b1).…”

Section: Morphology Of the Micronucleus And The Macronucleusmentioning

confidence: 99%

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Exploiting nuclear duality of ciliates to analyse topological requirements for DNA replication and transcription

Postberg

Alexandrova

Cremer

et al. 2005

Journal of Cell Science

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Spatial and temporal replication patterns are used to describe higher-order chromatin organisation from nuclei of early metazoan to mammalian cells. Here we demonstrate evolutionary conserved similarities and differences in replication patterns of micronuclei and macronuclei in the spirotrichous ciliate Stylonychia lemnae. Since this organism possesses two kinds of morphologically and functionally different nuclei in one cell, it provides an excellent model system to analyse topological requirements for DNA replication and transcription. Replication in the heterochromatic micronucleus occurs in foci-like structures showing spatial and temporal patterns similar to nuclei of higher eukaryotes, demonstrating that these patterns are inherent features of nuclear architecture. The `nanochromosomes' of the macronucleus are replicated in the propagating replication band. We show that it consists of hundreds of replication foci. Post-replicative macronuclear chromatin remains organised in foci. These foci are not randomly distributed throughout the macronucleus, indicating a higher-order organisation of macronuclear chromatin above the level of `nanochromosomes'. Both telomerase and proliferating cell nuclear antigen (PCNA) occur as foci-like structures in the rear zone of the replication band, suggesting that a wave of chromatin modification driven by a short or continuous exogenous signal permits the assembly of replication factories at predicted sites. We further show that transcription occurs at discrete sites colocalised with putative nucleoli and dispersed chromatin. Common principles of functional nuclear architecture were conserved during eukaryotic evolution. Moreover nuclear duality inherent to ciliates with their germline micronucleus and their somatic macronucleus may eventually provide further insight into epigenetic regulation of transcription, replication and nuclear differentiation.

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Section: Discussionmentioning

confidence: 99%

Section: Morphology Of the Micronucleus And The Macronucleusmentioning

confidence: 99%

Exploiting nuclear duality of ciliates to analyse topological requirements for DNA replication and transcription

Postberg

Alexandrova

Cremer

et al. 2005

Journal of Cell Science

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“…Various studies strongly suggest that chromatin in the macronucleus adopts a higher order organization above the level of nanochromosomes (Meyer & Lipps 1981, Murti & Prescott 2002, Postberg et al 2001, 2005. Macronuclear DNA is organized into domains of condensed chromatin separated from domains of dispersed chromatin.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of pre-rRNA and mRNA is directed to a chromatin-poor compartment in the macronucleus of the spirotrichous ciliate Stylonychia lemnae

2006

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In contrast to the chromosomal genome organization common to most eukaryotes, DNA in the macronucleus of spirotrichous ciliates like Stylonychia lemnae is organized into small gene-sized nanochromosomes. We intended to elucidate whether a spatial organization of nucleoli similar to other eukaryotes can be found in absence of typical chromosomes. Whereas micronuclei of Stylonychia exhibit homogenously stained heterochromatin and possess no nucleoli, macronuclear chromatin is compartmentalized and contains numerous putative nucleoli. Since the identity of these spherical structures has never been unequivocally demonstrated to date, we applied immunofluorescence techniques together with confocal laser scanning microscopy to identify nucleolar bodies in the macronucleus of Stylonychia and to analyse their spatial organization. We found that multiple spherical bodies, which fulfil nucleolar function, occupy a peripheral localization in mature macronuclei. Using fibrillarin/Nop1p as a nucleolar marker, we monitored the assembly of such nucleolar bodies during macronuclear differentiation. 3D-FISH experiments revealed that rRNA genes are mostly concentrated adjacent to but not inside of fibrillarin/Nop1p-containing bodies. We further showed that transcription sites for rRNA synthesis but also for mRNA synthesis occur predominantly at surfaces of nucleolar bodies and chromatin-poor spaces bordering condensed chromatin. Our data suggest that transcription of rRNA genes in the macronucleus of Stylonychia does not rely on a classical nucleolus-type organization. We assume that vectorial synthesis and processing of rRNA and mRNA is directed to a functional interchromatin compartment.

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“…The sexual phases of conjugation and autogamy are associated with the degradation of the old macronucleus and with the formation of a new one after division of the zygotic nucleus. This last step is known to involve the amplification, fragmentation and elimination of DNA and has been the subject of previous investigations in various ciliates (3,4,5,6). Chromosomal DNA fragmentation leads to an increase in the number and a reduction in the size of macronuclear chromosomes as compared to micronuclear ones.…”

Section: Introductionmentioning

confidence: 99%

Telomeric site position heterogeneity in macronuclear DNA ofParamecium primaurelia

1987

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SIn Paramecium primaurelia, the macronuclear gene encoding the G surface protein is located near a telomere. In this study, multiple copies of this telomere have been isolated and the subtelomeric and telomeric regions of some of them have been sequenced. The telomeric sequences consist of tandem repeats of the hexanucleotides C A2 or C A3. We show that the location where these repeats are added, which we caIl the telomeric site, is variable within a 0.6-0.8-kb region. These results are discussed in relation with the formation of macronuclear DNA.

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Organization of Genetic Material in the Macronucleus of Hypotrichous Ciliates

Cited by 18 publications

References 37 publications

Exploiting nuclear duality of ciliates to analyse topological requirements for DNA replication and transcription

Exploiting nuclear duality of ciliates to analyse topological requirements for DNA replication and transcription

Synthesis of pre-rRNA and mRNA is directed to a chromatin-poor compartment in the macronucleus of the spirotrichous ciliate Stylonychia lemnae

Telomeric site position heterogeneity in macronuclear DNA ofParamecium primaurelia

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