Recent Advances in the Genetics of Paramecium and Euplotes

Sonneborn, T. M.

doi:10.1016/s0065-2660(08)60488-5

Cited by 296 publications

(97 citation statements)

References 104 publications

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“…2-5). Hertwig (1889) gave the first detailed description of macronuclear amitosis and Sonneborn (1947) has summarized it in English. Briefly, Hertwig's account states that the macronucleus moves to the side of the cell away from the gullet, elongates and narrows, and divides into halves transversely.…”

Section: Resultsmentioning

confidence: 99%

Ultrastructure of Nuclear Division in Paramecium Aurelia II. Amitosis of the Macronucleus

Stevenson¹,

Lloyd²

1971

Aust. Jnl. Of Bio. Sci.

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Ultrastructural details of macronuclear amitosis in the ciliate P. aurelia are described. During amitosis the nuclear membrane remains intact, and there are no changes in the appearance of the nucleoli and chromatin bodies of the macronucleus. At the commencement of amitosis the nucleus adopts a smoother outline and a position in the cell opposite the gullet. This usually occurs at the time when the micronuclei are in metaphase of mitosis. At this stage, bands of microtubules are apparent in the cytoplasm, close to, and parallel with, the long axis of the nucleus. Microtubules also appear in the fibrous background region of the nucleus. The macronucleus then elongates and narrows; bands of microtubules are evident close to the inside of the nuclear membrane as this occurs. As karyokinesis proceeds (concurrently with cytokinesis) microtubules are found in all regions of the macronucleus, oriented along the long axis. At no stage of division do microtubules appear to be attached to the chromatin bodies of the macronucleus. Several aspects of macronuclear amitosis in ciliates are discussed.

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Section: Resultsmentioning

confidence: 99%

Ultrastructure of Nuclear Division in Paramecium Aurelia II. Amitosis of the Macronucleus

Stevenson¹,

Lloyd²

1971

Aust. Jnl. Of Bio. Sci.

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“…After reciprocal nuclear exchange, synkaryon formation occurs, meanwhile the old parental macronucleus breaks down into fragments and is eventually degraded. After two successive postzygotic divisions of the synkaryon, two of the products remain micronuclei, while the other two differentiate into new macronuclei, which later segregate to two daughter cells without division (Sonneborn, 1947). Macronuclear differentiation is accompanied by extensive DNA rearrangement of the germinal micronuclear genome, including chromosome fragmentation, addition of telomeres, and excision of numerous elements called internal eliminated sequences (IESs) from both coding and non-coding regions.…”

Section: Introductionmentioning

confidence: 99%

Preferential cleavage of Paramecium DNA mediated by the C. elegans Tc1 transposase in vitro

Nakayama

Endoh

2003

Genes Genet. Syst.

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In the ciliate Paramecium aurelia complex , thousands of internal eliminated sequences (IESs) are excised from the germline micronuclear DNA during macronuclear differentiation. Based on the resemblance of Paramecium IES end sequences to Tc1 transposon termini, it has been proposed that Paramecium IESs might have degenerately evolved from Tc1 family transposons, and still be removed by an enzyme homologous to a Tc1 transposase. In this study, we found that transposase preferentially cleaved (or nicked) 58 sites near the IESs in Paramecium DNA, at sequences consisting of TT or TCTA. Since one excision junction of the P. primaurelia W2 IES was included in such sites, this suggests that a Tc1-like transposase is involved in the IES excision process, although it is probably not a sole factor responsible for the precise cleavage. In addition, unmethylated substrate DNA appeared to decrease the cleavage specificity, suggesting an involvement of DNA methylation in the cleavage. Although these results do not directly address the transposon origin of Paramecium IESs, it is likely that the enzymatic machinery responsible for the initial cleavage is derived from a Tc1-like transposase. The mechanism necessary for precise excision is discussed, in relation to recent knowledge of IES excision obtained in Tetrahymena and Paramecium .

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“…In P. aurelia species complex, Sonneborn already reported that mating types are controlled cytoplasmically or caryonidally (see Sonneborn, 1947). My question was whether mating type of P. caudatum is also controlled in the same way.…”

mentioning

confidence: 98%

My Paramecium Study, Retrospect and Prospect

Hiwatashi

2001

Zoological Science

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Recent Advances in the Genetics of Paramecium and Euplotes

Cited by 296 publications

References 104 publications

Ultrastructure of Nuclear Division in Paramecium Aurelia II. Amitosis of the Macronucleus

Ultrastructure of Nuclear Division in Paramecium Aurelia II. Amitosis of the Macronucleus

Preferential cleavage of Paramecium DNA mediated by the C. elegans Tc1 transposase in vitro

My Paramecium Study, Retrospect and Prospect

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