A.S. Henderson

Transforming DNA integrates into the host chromosome

A series of rat liver cotransformed cell lines have been constructed containing from 5 to 100 copies of a variant human growth hormone gene. We have used hybridization in situ to demonstrate that most, if not all, cotransformed sequences reside in a chromosome of the host cell. In each of four cell lines examined, hybridization was restricted to a single chromosomal site with no extrachromosomal sites apparent. The site was invariant within each line; however, each line revealed a different site of integration for transforming sequences. In two of the four lines, transforming DNA resided at or near the site of gross chromosomal rearrangements, in one line near an rDNA site, and in one line in the middle of an apparently normal chromosome. Thus, insertion is not restricted to a unique chromosome or chromosomal region.

Variation in the number of genes for rRNA among human acrocentric chromosomes: correlation with frequency of satellite association

Grain counts after hybridization of 125I-rRNA to human chromosomes indicate numerical polymorphism at the rDNA sites. Prephotographing procedures decrease labeling but do not change the proportions of labeled RNA annealed to different chromosomes. A positive correlation was found between the frequency of participation of a given chromosome in satellite associations and its rDNA content by the criterion of grain count. Certain individual chromosomes are clear exceptions to this correlation.

Sequential silver staining and hybridization in situ on nucleolus organizing regions in human cells

Chromosome preparations from eight individuals were first stained with silver nitrate to reveal the nucleolus organizing regions (NORs) and then hybridized in situ with ribosomal RNA. In six individuals the size of the silver-staining regions was positively correlated with the amount of label present after hybridization in situ. Thus the variation in silver-staining intensity among chromosomes was largely explained by variation in the number of rDNA gene copies per NOR. However, in two individuals this correlation was absent, suggesting that other factors can also influence the size of the silver-staining region.

Variation in ribosomal rna gene number in mouse chromosomes.

Hybridization of 125-I-ribosomal RNA to mouse chromosomes in situ produced significant differences in grain count at known rDNA sites, depending on the strains from which they were derived. This is interpreted to mean that the number of rRNA genes in a given nucleolar chromosome, and in the entire genome, is polymorphic among strains and among outbred individuals.

Chromosomal distribution of rDNA in Pan paniscus, Gorilla gorilla beringei, and Symphalangus syndactylus: Comparison to related primates

Hybridization in situ was used to identify rDNA in chromosomes of the pygmy chimpanzee, mountain gorilla, and siamang gibbon. In contrast to other Pongids, and man, the gorilla has only two pairs of rDNA-containing chromosomes. The single pair in the siamang bears no resemblance to the nucleolar chromosome of the closely related lar gibbon. Pan paniscus and P. troglodytes have the same rDNA distribution, and similar karyotypes except in the structure of chromosome 23p. Grain counts over unbanded preparations show that the human, orangutan, and both chimpanzees have about the same total rDNA multiplicity.

Quantitation of ribosomal RNA genes in fetal human oocyte nuclei using rRNA: DNA hybridization in situ: Evidence for increased multiplicity

Abstract Several experimental observations provide evidence for the existence of an amplification-type phenomenon involving the genes for ribosomal RNA (rRNA) during meiotic prophase in the human oocyte. In previous investigations multiple micronucleoli, in addition to primary nucleoli, were shown to be present in late pachytene and in diplotene human oocyte nuclei. In the present study, detailed quantitative analysis of grain counts from more than 1 000 cells following hybridization in situ indicated the presence of greater than the expected 4C number of ribosomal genes in the oocyte nuclei, most notably in these same stages. The extent of this increase over the expected 4C amount of DNA complementary to rRNA was approx. 2-fold in oocytes early in meiotic prophase and rose to approx. 4-fold in late pachytene and early diplotene oocytes. These results constitute the first evidence for the presence of extra rDNA in mammalian oocyte nuclei, the occurrence of which is clearly consistent with earlier cytological and ultrastructural observations.

The chromosomal location of rDNA in selected lower primates

Hybridization in stiu was used to identify the chromosomes that carry rDNA in representative lower primates, including the baboons, Papio cynocephalus and Papio hamadryas; the colobus monkey, Colobus polykomos; the tree shrew, Tupaia glis; the lemur, Lemur fulvis; the saki, Pithecia pithecia; the marmoset, Saguinus nigricollis, and the spider monkey, Ateles geoffroyi. The marker chromosome, common to the Cercopithecines studied to date, carries the rDNA in the baboons. Another marker chromosome carries rDNA in a South American species, the spider monkey. A multichromosomal distribution of rDNA was demonstrated in the tree shrew, lemur, saki, and marmoset. None of the rDNA-containing chromosomes in the prosimians and New World monkeys show homology to the chromosomes that carry rDNA in the Hominids, Pongids, or Old World monkeys.

The site of 5S RNA genes in primates

A major site of genes for 5S RNA has been localized in representative members of the family Pongidae by means of hybridization in situ. These genes are shown to be concentrated in the most distal bands of the primate chromosome arm homologous to human chromosome 1q.

Biological Effects of EMFs

People have always considered the exposure to non-ionising radiation with scepticism. The prospect that exposure to electromagnetic fields (EMF) can have a deleterious effect or any effect on cellular behaviour has been debated in scientific and journalistic circles for some years. The drive to determine whether EMFs were involved in cellular behavioural changes is critical since environmental proximity to high voltage power lines and electric stations or the routine use of household appliances and cellular phones is increasing exponentially. Support for a deleterious effect gained impetus with the report that children whose homes were close to power lines had a higher frequency of leukemia. If cell signalling is influenced by EMF exposure, it provides further impetus to determine whether EMF exposure can cause or alter the propensity to cancer or have other deleterious effects in cells. Numerous laboratory studies both in vitro and in vivo have provided evidence that exposure to EMF induces a wide range of responses in biological systems.

The localization of rDNA in small, nucleolus-like structures in human diplotene oocyte nuclei

SummarySmall, nucleolus-like structures were demonstrated in the nuclei of human diplotene oocytes. At least some of these bodies were shown to be true micronucleoli by virtue of their ability to bind rRNA during RNA-DNA hybridization in situ.