Role of DNA topoisomerase I in Drosophila melanogaster male meiosis

DNA topoisomerase I functions as a molecular swivel and regulates the topological states of DNA and chromatin by creating a transient break in a single DNA strand in a duplex and religation of the break after the passage of another strand. DNA topoisomerases play important roles in DNA replication, transcription, recombination and other aspects of DNA metabolism.

Previous studies have shown that the 240 base-pair repetitive sequence within the intergenic spacer of ribosomal DNA repeats functions in X-Y chromosome pairing in Drosophila melanogaster males. A 16 base-pair high-affinity topoisomerase I cleavage site has been found in the 240 base- pair repeats and a model for achiasmatic chromosome pairing involving topoisomerase I has been proposed. In this study, the yeast FLP-FRT site- specific recombination system was used to fascilitate the study of the role of topoisomerase I in male meiosis using spermatocytes that are deficient in topoisomerase I.

Genetic studies of chromosome disjunction showed that the nondisjunction frequencies in the male and female experimental flies did not exhibit substantial increases over the wild-type frequencies and the heat- shock treated flies produced fewer progeny than the control flies. Immunocytological studies using anti-topoisomerase I antibody has not been able to identify any viable spermatocytes that are topoisomerase I-deficient. The results from both of these studies have suggested that DNA topoisomerase I is required for the development of spermatocytes in the male flies.