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Biomedical subjects

J G Gall

Publications and source records attributed to J G Gall.

At least 91 records · Page 5Linked to original sources
PubMed1976

Conformations of satellite DNAs.

X-ray fiber diffraction studies of satellite DNAs from Gecarcinus lateralis, Drosophila virilis and Mus musculus, all of which have highly repetitious base sequences but with different degrees of sequence complexity, reveal only classical polynucleotide duplex structures in contrast to some highly repetitious synthetic DNAs.

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PubMed1975

Differential replication of satellite DNA in polyploid tissues of Drosophila virilis.

Satellite DNA amounts were examined in adult tissues of Drosophila virilis, a species whose DNA contains three prominent satellites. Satellite amounts in DNA from six of the seven tissues were lower than in DNA from diploid (adult brain) tissue. Satellite amounts in adult ovary DNA, however, were equivalent to or greater than diploid levels. When DNA from pupal ovaries was examined, a 30% increase in satellite amounts over diploid levels was found. An RNA-DNA hybridization experiment showed that the ribosomal RNA genes in pupal ovary DNA were under-replicated relative to diploid DNA levels.

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PubMed1974

The amplified ribosomal DNA of dytiscid beetles.

During oogenesis in many animals there is a massive extrachromosomal synthesis of the genes for ribosomal RNA. In Dytiscid beetles, as in the toad Xenopus, the amplified ribosomal DNA occurs as circular molecules of different sizes. The circles fall into size classes that are integral multiples of a unit circle. It is probable that the unit circle contains the coding sequence for one precursor ribosomal RNA molecule plus accompanying spacer sequences.

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PubMed1974

Free ribosomal RNA genes in the macronucleus of Tetrahymena.

In the macronucleus of the ciliated protozoan, Tetrahymena pyriformis GL, the genes coding for 17S and 25S rRNA exist as free, extrachromosomal molecules. About 90% of the molecules are linear with a molecular weight of 12.6 x 10(6). Most of the remainder are circles of the same size, or lariats (circles with tails). A few dimers and oligomers are found. The extrachromosomal rDNA of Tetrahymena represents a kind of gene amplification that may be common among primitive eukaryotes.

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PubMed1974

Observations on early germ cell development and premeiotic ribosomal DNA amplification in Xenopus laevis.

The origin of premeiotic ribosomal DNA (rDNA) amplification in germ-line cells of Xenopus laevis has been examined using in situ RNA-DNA hybridization on cytological preparations, tritiated thymidine autoradiography, and isopycnic density gradient centrifugation. Primordial germ cells (PGC), from the time they first become localized in the genital ridge at day no. 4 of development, until approximately day no. 22, remain in an extended interphase condition. During this time PGC do not incorporate tritiated thymidine, have near diploid levels of rDNA as demonstrated by cytological RNA-DNA hybridization, and possess only one or two nucleoli. Starting on day no. 22-24, mitosis, sexual differentiation, and rDNA gene amplification all begin in the germ cells. Multiple nucleoli also make their appearance at this stage. Ribosomal DNA amplification continues in gonial cells as long as they remain mitotically active. Amplified copies of rDNA are lost from germ cells at the onset of meiotic prophase. This loss is probably permanent in the male germ line, but variable and temporary in the female germ line. Early gonial cells in the ovary have been deduced to have an average cycle time for each mitotic division of between 3.8 and 4.3 days at a temperature of 21 degrees C. Some oogonia appear to divide only four times before entering meiotic prophase, while the average during the initial wave of germ cell division is nine. Finally, a satellite DNA has been isolated from adult testes which has a density in neutral cesium chloride corresponding to the density of amplified oocyte rDNA. This satellite is not present in DNA isolated from somatic tissues of Xenopus.

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PubMed1973

Independent control of ribosomal gene replication in polytene chromosomes of Drosophila melanogaster.

The saturation values for ribosomal RNA hybridization have been determined for DNA from diploid and polytene tissues of Drosophila melanogaster. These values have been measured in XO and XX larvae which have, respectively, one and two nucleolus organizers in the diploid chromosome set. The results show that (1) in diploid cells the ribosomal (r)DNA is present in amounts proportional to the number of nucleolus organizers, (2) in polytene cells the rDNA is under-replicated with respect to the euchromatic DNA, and (3) in polytene cells the amount of rDNA is independent of the diploid number of nucleolus organizers. These observations suggest that somatic variations in rDNA content may involve independent polytenization of the nucleolus organizer without change in the number of ribosomal cistrons per organizer. The independent polytenization of rDNA is proposed as the chromosomal explanation for the relative increase in rDNA in flies of the XO constitution.

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PubMed1973

Isolation and characterization of mitochondrial DNA from Drosophila melanogaster.

Mitochondrial DNA (MtDNA) with a neutral buoyant density of 1.681 g/cm(3) has been isolated from unfertilized eggs of Drosophila melanogaster. This DNA is a circular molecule with an average length of 5.3 microm; it reassociates with a low C(0)t(1/2) after denaturation, and in alkaline isopycnic centrifugation it separates into strands differing in density by 0.005 g/cm(3). MtDNA isolated from purified mitochondria of unfertilized eggs or from total larval DNA melts with three distinct thermal transitions. The three melting temperature values suggest that the molecule may have three regions differing in average base composition. DNA isolated from unfertilized eggs of D. melanogaster contains approximately equal amounts of MtDNA and another DNA with a buoyant density of 1.697 g/cm(3), slightly less dense than main peak DNA. The possibility that the heavier DNA fraction consists of amplified ribosomal DNA was excluded by hybridization experiments, but otherwise nothing is known of its origin or function.

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PubMed1972

The timing of meiosis and DNA synthesis during early oogenesis in the toad, Xenopus laevis.

Recently metamorphosed female Xenopus laevis toads were injected with tritiated thymidine. Animals were kept at 20 degrees C and were sacrificed 1-23 days after isotope injection. Radio-autographs of squash preparations of the ovaries were made. The progress of labeled germ cell nuclei was followed to obtain information on the time course of early meiosis and extra-chromosomal DNA synthesis. Premeiotic S was estimated to take not more than 7 days. Leptotene takes 4 days, zygotene takes 5 days, and pachytene was estimated to be completed in about 18 days. The major period of amplification of the extrachromosomal DNA occurs in pachytene and takes about 13 days. A low level of synthesis was observed before and after this period, in zygotene and late pachytene-early diplotene, extending the total time for extrachromosomal DNA synthesis during meiosis to about 18 days. These data allowed the calculation to be made that one round of replication of the amplified DNA takes between 1.2 and 3.0 days. It was also found that in both oogonial and premeiotic interphases, the nucleolus-associated DNA shows asynchronous (probably late) labeling with respect to the chromosomes.

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PubMed1972

Chromosomal localization of repetitive DNA in the newt, Triturus.

The repetitive DNA sequences of the newt, Triturus viridescens, have been studied by nucleic acid hybridization procedures. Complementary RNA was synthesized enzymatically from unfractionated newt DNA. This RNA hybridized strongly to the centromeric regions of both somatic and lampbrush chromosomes It also bound to other loci scattered along the lengths of the chromosomes The amplified ribosomal DNA in the multiple oocyte nucleoli was demonstrated by in situ hybridization

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