Ribosomal RNA genes in germ line and somatic cells of Ascaris lumbricoides

Tobler, Heinz; Zulauf, Erich; Kuhn, Othmar

doi:10.1016/0012-1606(74)90300-5

Cited by 13 publications

(4 citation statements)

References 13 publications

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“…In these two species, the rDNA is organized in a rather homogeneous tandem array of very short 7000 bp repeating units. In contrast, the present report shows that the 300 ribosomal genes (6) of Ascaris 1Umkricoides, a DNA eliminating nematode, occur in two main rDNA size classes of 8800 bp and 8400 bp length. Moreover, we recently found a third rDNA class containing intervening sequences in its 26S rRNA coding region (Back it al-, in preparation).…”

Section: Introductioncontrasting

confidence: 90%

Structural organization of the two main rDNA size classes ofAscaris lumbricoides

1984

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The two main rDNA size classes in the genome of Ascaris lumbricoides consist of 8.8 kb and 8.4 kb long repeating units present in a quantitative ratio of roughly 10:1. They both contain the genes coding for 18 , 5.8S and 26S ribosomal RNAs. The length heterogeneity is due to a 450 bp long spacer region localized in the longer repeating unit which begins 870 bp upstream of the 5'-end 18S gene. A few additional microheterogeneities in base sequence occur at the 5'-end of the 26S gene. The 18S, 5.8S and 26S coding regions have been mapped on both the 8.8 kb and 8.4 kb repeating units and the localization of the 5'- and 3'-ends of the 18S and 26S genes has been performed by S1 protection. No intervening sequences are present in either coding region of the two main rDNA size classes.

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Section: Introductioncontrasting

confidence: 90%

Structural organization of the two main rDNA size classes ofAscaris lumbricoides

1984

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“…In order to test this hypothesis, saturation hybridization experiments 43 Recently, we have analyzed the structural organization of the ribosomal genes in Ascaris lumbricoides in much more detail and found that the rDNA cluster of Ascaris lumbricoides exists in two main size classes of 8.8 kb and 8.4 kb, the length heterogeneity being due to a 450 bp long insertion located in the non-transcribed spacer region of the larger rDNA unit 3. The quantitative ratio of the two rDNA size classes is on the average roughly 10:1 in the investigated wild-type population of Ascaris lumbricoides, but varies to a great extent between different individuals".…”

Section: Germ Line and Somatie Cells Contain The Same Percentage Of Gmentioning

confidence: 97%

Germ line — soma differentiation inAscaris: A molecular approach

et al. 1985

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Summary. The early ontogenetic segregation of germ line and somatic ceils in the animal kingdom is phylogenetically very old and represents probably the first step in differentiation. While this phenomenon has been shown to occur in various animal phyla, it seems to be completely missing in the plant kingdom. In several animal species, the segregation of the germ and somatic cell lines is accompanied by the loss of whole or parts of chromosomes in the presumptive somatic cells. The cause of the chromatin diminution process as well as the significance of the germ line limited DNA sequences in species undergoing chromatin or chromosome loss still remain unknown. However, using modern biochemical and molecular biological techniques, it has become possible to analyze the process of chromatin diminution and the composition of the germ line specific DNA sequences at the molecular level.In Ascaris lumbricoides, about a quarter of the total amount of germ line DNA is eliminated from the presumptive somatic cells during chromatin diminution. Hybridization experiments revealed that germ line and somatic DNA contain the same percentage of 18S+28S rRNA genes. Therefore, chromatin diminution does not serve to discard large amounts of rRNA-coding genes from the germ line cells. On the other hand, over 99 %, but not all satellite DNA sequences present in the germ line genome, are expelled from the presumptive somatic cells by chromatin diminution. Molecular cloning and sequence analysis of different restriction endonuclease fragments isolated from the germ line satellite DNA indicated that this eliminated satellite is composed of a whole set of related variant sequences, which differ by small deletions, insertions and single base substitutions. Members of the same variant class are tandemly linked and therefore physically separated from other variant classes. By comparing all the determined sequences, it was possible to establish a 121 bp long and AT rich consensus sequence which itself exhibits an 11 bp long internal short range periodicity. We have no indication for transcriptional activity of the satellite DNA sequences at any stage or tissue tested. Evidence is accumulating that the eliminated DNA contains also other DNA sequences apart from the class of highly repetitive satellite DNA.

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“…This observation is of particular interest since somatic cells from Ascaris lumbricoides contain about 25% less DNA than germ line cells due to the process of chromatin elimination that takes place during early cleavage divisions of development (7,23,24). We have already shown (25) By in situ hybridization of fluorochrome-labelled 18S + 26S rRNA to metaphase and anaphase chromosomes of spermatocytes I, we were able to localize the rRNA genes of Ascaris lumbricoides on a single, medium-sized autosome (cf. Figs.…”

Section: Methodsmentioning

confidence: 87%

“…3 and 4). Ascaris 2Imbriicoides has about 300 ribosomal genes per haploid genome (25) and its 18S + 26S rRNA coding regions cover together approximately 5300 nucleotides (see preceding paper (1)). The sensitivity of the applied method is such that 220.000 bp or less are detectable with an 80 nucleotide long labelled probe, provided the tested sequence is located in a single spot (5).…”

Section: Methodsmentioning

confidence: 99%

Chromosomal arrangement of the two main rDNA size classes ofAscaris lumbricoides

1984

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The two main rDNA size classes of 8.8 kb and 8.4 kb length from Aaraxis lumbricoides, which comprise more than 95% of the total nuclear rDNA, are arranged as internally homogeneous clusters and are not intermingled with each other. The rRNA genes are present on a single autosomal locus as could be demonstrated by in situ hybridization of fluorochrome-labelled 18S and 26S rRNA to metaphase chromosomes of spermatocytes I. The quantitative ratio of the two rDNA size classes varies largely between individuals being on the average roughly 10:1 in the investi-

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Ribosomal RNA genes in germ line and somatic cells of Ascaris lumbricoides

Cited by 13 publications

References 13 publications

Structural organization of the two main rDNA size classes ofAscaris lumbricoides

Structural organization of the two main rDNA size classes ofAscaris lumbricoides

Germ line — soma differentiation inAscaris: A molecular approach

Chromosomal arrangement of the two main rDNA size classes ofAscaris lumbricoides

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