Rearrangements between irradiated chromosomes in three-species radiation hybrid cell lines revealed by two-color in situ hybridization

Micronuclei as a biological endpoint for genotoxicity: A minireview

The in vitro micronucleus assay has now been applied in many laboratories. This endpoint is useful in biomonitoring or ecotoxicology, as a sensitivity measure of human cells in cancer treatment and also to replace or supplement other in vitro genotoxicity assays. Learning more about the mechanisms of micronucleus formation allows conclusions about its biological significance. It has been demonstrated that disturbance of the mitotic apparatus (spindle, kinetochores) as well as impaired function of topoisomerase II can be involved in micronucleus formation. In addition, the roles of changes in DNA-conformation that are induced by alterations in the status of cytosine-methylation and of the cellular DNA repair capacity have been shown. The fate of micronucleus-containing cells is not known: the cells may theoretically be cytostatic and micronucleus-formation may therefore be a way of the organism to eliminate genetic damage or the cells may survive the loss of that chromosomal material and develop into transformed cells. Published data and ideas of selected areas within this field are reviewed.

Analysis of micronuclei in blue mussels and fish from the Baltic and North Seas

Micronuclei (MN) were analyzed in erythrocytes of flounder (Platichthys flesus) and wrasse (Symphodus melops) and in gill cells of blue mussels (Mytilus edulis). The organisms were collected from three study stations in the Baltic Sea and from seven stations in the North Sea (Karmsund area, Norway) 4 times. The statistically significant differences obtained were related to the season, sex of the fish, and sampling locality. Higher MN frequencies were found in fish and mussels collected from the most polluted study stations in the North Sea. The same tendency could be described in the Baltic Sea; however, it was masked by the recent oil spill from the Butinge oil terminal. Our results showing higher MN frequencies in presumably what were the most polluted study locations suggest that MN tests in fish and mussels may be used for the detection of genotoxic effects in a marine environment. The endpoint is well characterized and can be easily recognized, and the technique is convenient to use in field samplings following standard procedures and protocols.

Estimating physical distances from radiation hybrid mapping data

Radiation hybrid mapping has become an established tool for building physical maps. It represents a powerful way of constructing YAC contigs and high-resolution maps for positional cloning experiments. Ideally, radiation hybrids should not only provide support for the true order of the markers, but also accurate estimates of the physical distances between them. Statistical analysis of radiation hybrids has proved difficult because of the number of parameters (representing the fragment retention probabilities) that must be estimated, and simplifying assumptions are needed to analyze large numbers of markers simultaneously. The ramifications of these assumptions for the calculation of physical distances are investigated. A simple two-locus model is presented to demonstrate that variation in marker retention can lead to distortions in the estimates of distance. Multilocus simulations show that, when marker retention is constant across the chromosome, good estimates of physical distance can be derived using simple models of retention. However, further simulations exploring variable retention schemes demonstrate that significant errors in the estimates of map distances can occur. Ways of minimizing these distortions are discussed.