Nuclear DNA

About: Nuclear DNA is a research topic. Over the lifetime, 3933 publications have been published within this topic receiving 185830 citations.

Genome size in mammals.

Abstract: Nuclear DNA amounts of fifteen species of placental mammals were determined by Feulgen cytophotometry. Relative values for several widely used species have been ascertained with an error of only a few percent. Absolute values (picograms or numbers of nucleotide pairs) can be determined with an error of about ten percent. The largest known mammalian genome contains about twice the DNA of the smallest one. The modal diploid DNA amount for mammals is slightly above eight picograms.

Cytoplasmic inheritance and its effects on development and performance

Abstract: In contrast to nuclear inheritance, cytoplasmic inheritance in mammals is derived mostly, if not exclusively, from the maternal line. Mitochondria, and their DNA molecules (mtDNA), are the genetic units of this method of inheritance. Mammalian mtDNA codes for 13 enzymes used in the mitochondrial energy-generating pathway, oxidative phosphorylation, 22 tRNAs and two rRNAs. Although all transcripts of mtDNA and their translational products remain in the mitochondria, most proteins used in mitochondria are from nuclear DNA and are imported after synthesis on cytoplasmic ribosomes. Spermatozoa introduce a small number of mitochondria into the cytoplasm of the egg at fertilization, which appear to be digested soon after penetration. Although the paternal contribution of mtDNA to the offspring is not believed to occur in mammals, some interspecific crosses have suggested that it does occur. Experiments with animals derived from reconstituted embryos, using nuclear or cytoplasmic transplantations, suggest that nuclear-mitochondrial interactions are important but not essential in the survival and replication of exogenous mitochondria introduced into the egg. As the levels of heteroplasmy varied in several tissues of animals derived from reconstituted embryos, it is suggested that differential partitioning of mitochondria occurs during embryogenesis. Mitochondrial morphology changes substantially during oogenesis and throughout early cleavage stages. Somatic morphology and normal replication patterns are regained at the blastocyst stage. In pig oocytes and embryos, mitochondria aggregate and are closely associated with endoplasmic reticulum, lipid granules and large vesicles. Although the direct correlation of mitochondrial genes with reproductive traits is still unclear, some human degenerative diseases and performance traits in cattle can be related directly to specific mtDNA polymorphisms. In pigs, reciprocal-cross comparisons have indicated greater offspring parent similarity with dam than sire for lean:fat ratio. A difference was also observed for oxygen consumption and oxidative phosphorylation, but not for anaerobic energy metabolism, in a pig reciprocal-cross experiment. Information on the transmission of mtDNA and its effects on performance will have many implications not only for our understanding of mitochondrial genetics but also for the increased productivity of animals. There are also potential ramifications to the animal cloning industry.

DNA repair and chromatid anomalies in mammalian cells exposed to 4-nitroquinoline 1-oxide

Abstract: The oncogenic and mutagenic 4-nitroquinoline 1-oxide (4NQO) induces DNA-repair synthesis (unscheduled DNA synthesis) in diploid, aneuploid, normal and neoplastic human and Syrian-hamster cells. DNA-repair synthesis occurs in nuclei at G1, G2 and S-phase and in metaphase chromosomes of Syrian-hamster cells exposed to 4NQO. DNA-repair synthesis was separated from DNA-replication synthesis associated with chromosome replication at S-phase by arginine deprivation. The degree of [ 3 H]TdR incorporation into nuclear DNA is dependent on the dose of 4NQO (5·10 −8 to 1·10 −5 M ) and on the amount of DNA per cell. The time course of DNA-repair synthesis induced by 4NQO or UV was examined on non-dividing cells which were arrested by an arginine-deficient culture medium: an early occurring peak is followed by an abrupt decline at about 8 h post-treatment which is succeeded by a prolonged low level incorporation of [ 3 H]TdR. The effect of a completed and uncompleted repair synthesis on the flow of cells into S-phase and on the frequency of chromosome anomalies was studied on cells arrested by arginine deprivation and triggered to divide by addition of arginine. There appears to be a relationship between the degree of repair synthesis and on the other hand frequency of cells entering S-phase, incidence of metaphase plates with chromatid breaks, flow of cells from G2 into pro-metaphase and “uncoiling” of metaphase chromosomes or heterochromatic segments of interphase nuclei.

Satellite DNA and cytogenetic evolution. DNA quantity, satellite DNA and karyotypic variations in kangaroo rats (genus Dipodomys).

Abstract: The genusDipodomys (kangaroo rats) exhibits major interspecies variations in the proportions of highly reiterated satellite DNA sequences in the genome as well as in the chromosome number and the proportions of uni-armed and bi-armed chromosomes. For nearly all of the approximately 22 species of the genus and several subspecies, liver DNA was distributed in neutral CsCl buoyant density gradients into four fractions: principal DNA (1.698 g/ml), intermediate-density DNA (1.702 g/ml), MS satellite (1.707 g/ml) and HS (heavy) satellites (1.713 g/ml). The total nuclear DNA content of diploid liver cells measured in eleven species by quantitative cytophotometry, ranged from 6.9 to 10.9 pg. These data were correlated with known features of the karyotypes of individual species. The salient findings were: (1) that interspecies variations in diploid chromosome number cluster at 52–54, 60–64 and 70–72 (2) that high total nuclear DNA was associated with high chromosome number, and with relatively large amounts of satellite DNA (3) that a high ratio of HS satellites to intermediate-density DNA was generally correlated with a predominance of metacentric and submetacentric chromosomes (high fundamental number). The relationships of satellite DNA to karyotype structure reveal a new level of hierarchy in the genome that appears capable of exerting global control over environmental adaptation and the evolution of new species. This mechanism is consistent with recent hypotheses that changes in the macro-structure of the genome are more important than point mutations in facilitating the rapid phases of animal evolution.