DNA of ciliated protozoa: DNA sequence diminution during macronuclear development of oxytricha

Lauth, M.R.; Spear, Brian B.; Heumann, John M.; Prescott, David M.

doi:10.1016/0092-8674(76)90256-7

Cited by 166 publications

(101 citation statements)

References 17 publications

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“…These DNA pieces are produced by fragmentation of polytene chromosomes in postconjugative cells (12,13), and the process of macronuclear development from micronuclei results in considerable reduction in DNA sequence complexity (14). As was shown by Lawn and coworkers (15), macronuclear DNA is heterodisperse, but a particular DNA sequence in the macronucleus is found in a single size class of DNA molecules or in a small variety of discrete sizes.…”

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confidence: 96%

“…The (14). Because macronuclear DNA is composed of a large diversity of sequences, nonrandom base sequence is an unlikely explanation of the physical properties.…”

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confidence: 99%

“…The fractions that contained DNA were pooled, and the DNA was precipitated and then dissolved in 10 mM Tris-HCl, pH 7.8/1 mM Na2EDTA. The 32P-labeled DNA had a specific activity of about 1500 cpm/,tg.Macronuclei from Oxytricha were prepared essentially as described (14). Macronuclei were lysed in 2% Sarkosyl/0.5 M NaCl/0.…”

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confidence: 99%

“…Macronuclei from Oxytricha were prepared essentially as described (14). Macronuclei were lysed in 2% Sarkosyl/0.5 M NaCl/0.…”

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confidence: 99%

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Macronuclear DNA of the hypotrichous ciliate Oxytricha fallax

Rae

Spear

1978

Proc. Natl. Acad. Sci. U.S.A.

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DNA in the macronuclei of Oxytricha fallax, as in other hypotrichous ciliate protozoa, exists as small, achromosomal molecules rather than in chromosomes. We report studies on 0. fallax DNA using physicochemical procedures and nucleic acid hybridization. Macronuclear DNA molecules range in size from 22 kilobase pairs (kb) to about 0.5 kb. The DNA has a buoyant density in CsCl of 1.694 gcm-3 and a melting temperature in 15 mM NaCl/1.5 mM sodium citrate, pH 7, at 65.40. These values correspond to 34.7% Gua + Cyt and 28.1% Gua + Cyt, respectively, and base composition determined by thin-layer chromatography of nucleotides is 32.4% Gua + Cyt. The only modified nucleotide that is detectable is N6-methyldeoxyadenylate (0.2%), and the amount and kind of modification cannot account for the discrepancies in nucleotide composition determination by the three methods. The (rDNA) in the oocytes of amphibia (1, 2) and some insects (3, 4) and in the ciliate protozoa Tetrahymena (5, 6) and Paramecium (7). rDNA is also extrachromosomal in Physarum (8) and Dictyostelium (9). In Tetrahymena macronuclei (10) and in Physarum, rDNA is in the form of palindromic dimers. In Paramecium and other organisms, amplified genes for rRNA are tandemly repeated several to many times in extrachromosomal DNA molecules.Hypotrichous ciliate protozoa such as Oxytricha have a macronuclear genome comprised entirely of "extrachromosomal" or "achromosomal" DNA (11). These DNA pieces are produced by fragmentation of polytene chromosomes in postconjugative cells (12,13), and the process of macronuclear development from micronuclei results in considerable reduction in DNA sequence complexity (14). As was shown by Lawn and coworkers (15), macronuclear DNA is heterodisperse, but a particular DNA sequence in the macronucleus is found in a single size class of DNA molecules or in a small variety of discrete sizes.In this report, characteristics of the achromosomal macronuclear DNA of Oxytricha fallax are presented. 0. fallax is related to the unidentified species studied in Prescott's laboratory (15), but it is distinguished from the latter by its smaller size, by a different DNA buoyant density in CsCl, and by having two micronuclei per cell instead of four. Nevertheless, the processes of conjugation, macronuclear development, and vegetative reproduction in 0. fallax follow the general pattern described for other hypotrichs. Our reported studies on 0. fallax have concentrated on the genes for 25S and 19S rRNAs and for 5S rRNA. These genes have been localized to relatively small, nonpalindromic DNA, little larger than necessary to accomodate single coding sequences.MATERIALS AND METHODS Culture and In Vivo Labeling of 0. fallax. Cultures of 0. fallax were obtained from the Indiana University collection. Cells were grown in 0.1% Cerophyl medium with Chlamydonas reinhardtii as a food source. Medium was supplemented either with heat-killed Escherichia coli or with killed Klebsiella aerogenes in a vitamin/stigmasterol mixture (16). Cultures were harves...

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mentioning

confidence: 96%

“…The (14). Because macronuclear DNA is composed of a large diversity of sequences, nonrandom base sequence is an unlikely explanation of the physical properties.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

“…Macronuclei from Oxytricha were prepared essentially as described (14). Macronuclei were lysed in 2% Sarkosyl/0.5 M NaCl/0.…”

mentioning

confidence: 99%

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Macronuclear DNA of the hypotrichous ciliate Oxytricha fallax

Rae

Spear

1978

Proc. Natl. Acad. Sci. U.S.A.

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“…As the DH plants originated from the haploid vegetative cells in the pollen, the results might suggest a difference between the vegetative cells and the generative cells in the pollen during cellular differentiation (De Paepe et al, 1981). The distinction might correspond to the differences in DNA organization known to exist between macro-and micro-nuclei of ciliated protozoa (Lauth et al, 1976).…”

Section: Development-induced Dna Content Variationmentioning

confidence: 98%

Developmental and environmental variation in genomes

2009

Heredity

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The genetic make-up of an organism, established at fertilization, is not conventionally expected to change during development unless mutation occurs. However, there is actually evidence that considerable variation can arise. Some of these changes may occur in response to the environment. This article reviews such variations in genome size or DNA content (excluding ploidy-level changes). The variation can be generated by processes, including high-frequency chromosomal recombination, transposition, cis-element-enhanced gene amplification and repetitivesequence-based changes in nuclear DNA content. Environmentally induced and developmentally regulated genomic variation (ED-genomic variation or ED-genetic variation) can be found in both coding and non-coding sequences, and is often non-Mendelian in its inheritance pattern. Changes can depend on development (for example, propagation method, seed/fruit position on plants, embryo stage, etc.) and occur in response to the environment (for example, light, temperature, herbicide, salinity, fertilizer, land slope direction, pathogen infection, etc.). Some plants have meiotic (or rejuvenation) corrections, which restore their genome sizes to a certain degree. However, Mendelian inheritance and acquired inheritance of the variants occur, and both inheritance types may be different expressions evolved for the same adaptive responses. With this perspective, the terms 'pure-breeding line' or 'stable cultivar' may only be appropriate for a given mode of reproduction or propagation, and for a given environment. ED-genomic variation appears to be an essential component of differentiation, development and adaptation. Consequently, modern molecular biology tools, such as microarray hybridization and new sequencing technology, should be directed towards a more comprehensive evaluation of ED-genomic variation.

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RNA‐Mediated Somatic Genome Rearrangement in Ciliates

Bracht

2017

Somatic Genome Variation in Animals, Plants, and Microorganisms

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DNA of ciliated protozoa: DNA sequence diminution during macronuclear development of oxytricha

Cited by 166 publications

References 17 publications

Macronuclear DNA of the hypotrichous ciliate Oxytricha fallax

Macronuclear DNA of the hypotrichous ciliate Oxytricha fallax

Developmental and environmental variation in genomes

RNA‐Mediated Somatic Genome Rearrangement in Ciliates

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