Polytene chromosomes and nucleic acid metabolism during macronuclear development in Euplotes

Rao, M. V. Narasimha; Ammermann, Dieter

doi:10.1007/bf00326082

Cited by 32 publications

(12 citation statements)

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“…eurysotmus exconjugants at similar stages of macronuclear development . Moreover, it was demonstrated (17,18) that the limited RNA incorporation detected in the case of Euplotes was not restricted to certain bands (puffs) as in dipterans . Thus the polytenization does not appear to enhance the RNA-synthetic capacity of the macronuclear anlagen .…”

Section: Discussionmentioning

confidence: 99%

“…It has been proposed that the DNA loss in Euplotes and Stylonychia anlagen may be genetically selective (9,17,18) . Ammermann (1) found that there is approximately a diploid amount of DNA remaining in the anlage following the destruction of the polytene chromosomes in Stylonychia .…”

Section: Discussionmentioning

confidence: 99%

“…Recent studies of macronuclear differentiation following conjugation in a number of ciliates have revealed the presence of long cross-banded chromosome-like structures within the macronuclear anlagen at early stages of exconjugant development (1,4,6,15,17,18) . Because the width of such strands increases during an initial period of DNA build-up within the macronuclear anlagen, and because DNA is concentrated in the banded regions, these strands have been interpreted as polytene chromosomes similar to those found in larval dipteran tissues .…”

Section: Introductionmentioning

confidence: 99%

“…Because the width of such strands increases during an initial period of DNA build-up within the macronuclear anlagen, and because DNA is concentrated in the banded regions, these strands have been interpreted as polytene chromosomes similar to those found in larval dipteran tissues . Although a specificity of banding pattern along the macronuclear chromosomes has not yet been established, some of the bands have been reported to resemble the "puffs" found on dipteran giant chromosomes (12,18) . In the most carefully studied cases, the hypotrichs Stylonychia mvtilus (1) and Eupootes woodruffi (18), it has been found that following the period of maximum polyteny, the giant chromosomes break down and the bulk of their DNA is degraded (1)(2)(3)18) .…”

Section: Introductionmentioning

confidence: 99%

“…Although a specificity of banding pattern along the macronuclear chromosomes has not yet been established, some of the bands have been reported to resemble the "puffs" found on dipteran giant chromosomes (12,18) . In the most carefully studied cases, the hypotrichs Stylonychia mvtilus (1) and Eupootes woodruffi (18), it has been found that following the period of maximum polyteny, the giant chromosomes break down and the bulk of their DNA is degraded (1)(2)(3)18) . After an interval of several hours, the remaining DNA of the anlagen replicates many times, without the formation of discernible chromosomes, to form the "polyploid," RNA-producing macronucleus of the vegetative cell .…”

Section: Introductionmentioning

confidence: 99%

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COMPARTMENTALIZATION OF THE DEVELOPING MACRONUCLEUS FOLLOWING CONJUGATION IN STYLONYCHIA AND EUPLOTES

Kloetzel

1970

The Journal of Cell Biology

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The development of the macronucleus following conjugation in the hypotrichous ciliates Euplotes and Stylonychia has been examined with the electron microscope. Banded polytene chromosomes can be seen in thin sections of the macronuclear anlagen during the early periods of exconjugant development. As the chromosomes reach their maximum state of polyteny, sheets of fibrous material appear between the chromosomes and transect the chromosomes in the interband regions. Individual bands of the polytene chromosomes thus appear to be isolated in separate compartments. Subsequently, during the stage when the bulk of the polytenic DNA is degraded (1), these compartments swell, resulting in a nucleus packed with thousands of separate spherical chambers. Individual chromosomes are no longer discernible. The anlagen retain this compartmentalized condition for several hours, at the end of which time aggregates of dense material form within many of the compartments. The partitioning layers disperse shortly before replication bands appear within the elongating anlagen, initiating the second period of DNA synthesis characteristic of macronuclear development in these hypotrichs. The evidence presented here suggests that the "chromatin granules" seen in the mature vegetative macronucleus represent the material of single bands of the polytene chromosomes seen during the earlier stages of macronuclear development. The possibility is also discussed that the degradation of DNA in the polytene chromosomes may be genetically selective, which would result in a somatic macronucleus with a different genetic constitution than that of the micronucleus from which it was derived.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%