Rearrangement of repeated DNA sequences during development of macronucleus in<i>Tetrahymena thermophila</i>

Iwamura, Yukio; Sakai, Masaharu; Muramastu, Masami

doi:10.1093/nar/10.14.4279

Cited by 16 publications

(11 citation statements)

References 14 publications

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“…Orias and Baum (28) have shown that mating-type differentiation in T. thermophila is strongly influenced by delayed refeeding of conjugating cells during macronuclear development. Because other genomic changes have been observed to occur in the period 10 to 24 h after initiation of mating ( (20), and 13 of 20 (38) randomly selected cloned micro-and macronuclear DNA segments contained eliminated sequences. In many of these clones the eliminated sequences were repetitive in the micronuclear genome.…”

Section: Resultsmentioning

confidence: 99%

Reproducible and variable genomic rearrangements occur in the developing somatic nucleus of the ciliate Tetrahymena thermophila.

Howard¹,

Blackburn²

1985

Mol. Cell. Biol.

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We analyzed the extent, reproducibility, and developmental control of genomic rearrangements in the somatic macronucleus of the ciliate Tetrahymena thermophila. To exclude differences caused by genetic polymorphisms, we constructed whole-genome homozygotes, and we compared the homozygous progeny derived from single macronuclear differentiation events. This strategy enabled us to identify a novel form of variable rearrangement and to confirm previous findings that rearranged sequences occur at a high frequency in the Tetrahymena genome. Rearrangements studied here were deletions of both unique and interchromosomally dispersed repetitive DNA sequences involving DNA rejoining of internal, nontelomeric regions of macronuclear DNAs. We showed that although rearrangements of some sequence classes are reproducible among independently developed macronuclei, other specific sequence classes are variably rearranged in macronuclear development. The variable somatic genomes so produced may be the source of phenotypically variant cell lines.A long-standing question in eucaryote development is the extent and nature of DNA rearrangement during development. Irreversible differential gene alterations have been found in a number of widely separated systems. Developmentally programmed examples of these include the chromosomal diminution found in nematodes (reviewed in reference 36), some insects and crustaceans (reviewed in references 5 and 35), and ciliates (reviewed in references 15, 24, and 25) and DNA rearrangements which occur in antibody-producing lymohocytes (reviewed in reference 34).The ciliated protozoan Tetrahymena thermophila affords an excellent model system to determine the extent, nature, and developmental timing of rearrangements during development of the somatic nucleus. T. thermophila is a unicellular organism containing two nuclei, a transcriptionally inactive germline nucleus (micronucleus) and a somatic, amitotically dividing macronucleus which is the site of gene expression. In the sexual process, conjugation, haploid micronuclei generated by meiosis are exchanged between the paired cells and subsequently fused. A division product of the newly diploid micronucleus in each cell differentiates into a new macronucleus, replacing the old macronucleus, which is destroyed (for reviews, see references 12, 14, and 15). Since these cells subsequenly divide vegetatively by binary fission in the absence of conjugation (which requires specific culture conditions as well as interaction between two cells of different mating types), large clonal populations can be obtained at given stages of development, and pure preparations can be made of macronuclei and their parent micronuclei.

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Section: Resultsmentioning

confidence: 99%

Reproducible and variable genomic rearrangements occur in the developing somatic nucleus of the ciliate Tetrahymena thermophila.

Howard¹,

Blackburn²

1985

Mol. Cell. Biol.

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“…Three types of DNA segments have now been described in terms of their behavior during MAC development in Tetrahymena themophila: those that are invariably eliminated [ 16,17,23], those that are retained in all cell lineages [24,25], and those that are retained in some cell lineages but eliminated in others [this report; 241. Facultatively persistent sequences as well as those totally eliminated are found together on MIC DNA clone pT1008.…”

Section: Discussionmentioning

confidence: 99%

Macronuclear persistence of sequences normally eliminated during development in Tetrahymena thermophila

White

Allen

1985

Dev. Genet.

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During conjugation in the ciliated protozoan, Tetrahymena thermophilu , a somatic MACronucleus develops from the germinal MICronucleus. Ten to 20 percent of the MIC genome is eliminated during this process. Three repetitive families have been identified which have different levels of repetition in the MIC and are eliminated to different degrees in the MAC. Some members of two of these families persist in the MAC. In this study, we have looked at these persistent sequences in the MAC of cell lines from a variety of sources including several inbed strains, two sets of caryonides, caryonidal subclones, and vegetatively aged cell clones. The results suggest that the sequences that remain in the MAC have a genetic predisposition to persist. However, epigenetic variations occur as the MAC develops so that only some of the persistent sequences are actually observed in a particular MAC. Polymorphisms may be generated if alternative processing of a single MIC segment occurs. These polymorphisms can later be resolved by phenotypic assortment during vegetative growth. These facultatively persistent sequences appear to differ from sequences previously described in this organism.

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“…Studies of DNA renaturation kinetics indicate that 10-20% absent from the macronucleus of T. thermophila (7). This conclusion is supported by comparisons of randomly chosen regions of the micronuclear genome with their macronuclear counterparts (8,9,10,11,12). Most of the eliminated sequences are moderately repetitive (8,9,10,12), and are dispersed on all five micronuclear chromosomes (8,10,12).…”

Section: Introductionmentioning

confidence: 84%

Developmentally regulated telomere addition inTetrahymena thermophila

1988

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To investigate the developmentally programmed telomere addition that accompanies chromosome fragmentation during macronuclear differentiation in Tetrahymena thermophila, five representative telomeric regions from the macronucleus were cloned and characterized in detail. The sequences adjacent to the telomeric (C4A2:T2G4) repeats on these five macronuclear ends had no significant sequence homology or shared secondary structure. Two developmentally independent examples of one macronuclear telomere had a 5 base pair difference in the position of the junction between the telomeric repeats and the adjacent sequences. A telomere-adjacent sequence, in the form of a synthetic oligonucleotide, was unable to prime the addition of telomeric repeats in vitro. The implications of these results for the mechanisms underlying developmentally programmed chromosome fragmentation and telomere addition in Tetrahymena are discussed.

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Rearrangement of repeated DNA sequences during development of macronucleus inTetrahymena thermophila

Cited by 16 publications

References 14 publications

Reproducible and variable genomic rearrangements occur in the developing somatic nucleus of the ciliate Tetrahymena thermophila.

Reproducible and variable genomic rearrangements occur in the developing somatic nucleus of the ciliate Tetrahymena thermophila.

Macronuclear persistence of sequences normally eliminated during development in Tetrahymena thermophila

Developmentally regulated telomere addition inTetrahymena thermophila

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