Abstract
Ethidium bromide (EB) is an intercalating inhibitor of topoisomerase II and its activities are related to chemotherapeutic drugs used in anti-cancer treatments. EB promotes several genotoxic effects in exposed cells by stabilising the DNA-enzyme complex. The recombinagenic potential of EB was evaluated in our in vivo study by the loss of heterozygosity of nutritional markers in diploid Aspergillus nidulans cells through Homozygotization Index (HI). A DNA repair mutation, uvsZ and a chromosome duplication DP (II-I) were introduced in the genome of tested cells to obtain a sensitive system for the recombinagenesis detection. EB-treated diploid cells had HI values significantly greater than the control at both concentrations (4.0 x 10-3 and 5.0 x 10-3 mM). Results indicate that the intercalating agent is potentially capable of inducing mitotic crossing-over in diploid A. nidulans cells.
Highlights
DNA topoisomerase II is a ubiquitous enzyme that regulates DNA topologic interconversion during replication, transcription and genetic recombination decreasing torsional stress in DNA by introducing transient protein-bridged DNA breaks in both DNA strands
A. nidulans duplication strains are very unstable at mitosis, with slow growth caused by genetic imbalance
It has been shown that genome balance of heterozygous diploids for duplicated segments may be restored by deletion and mitotic crossing-over (Case and Roper, 1981)
Summary
DNA topoisomerase II (topo II) is a ubiquitous enzyme that regulates DNA topologic interconversion during replication, transcription and genetic recombination decreasing torsional stress in DNA by introducing transient protein-bridged DNA breaks in both DNA strands. Through this function, topo II plays an essential role in the maintenance of genetic material integrity (Mo and Beck, 1999; Godard et al, 2002). Rather than inhibiting the catalytic activity of the topo II enzyme, they act by increasing levels of topo II mediated DNA cleavage This mechanism converts essential enzyme into a potent cellular toxin, inducing apopitosis, cell cycle arrest and genotoxicity (Nitiss and Beck, 1996; Attia et al, 2002). Long-term adverse effects of this class of chemotherapic items, such as infertility and increased incidence of secondary malignancies, have been shown (Tiburi et al, 2002)
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