Coaction of DNA topoisomerase IIIα and a RecQ homologue during the germ-line mitosis in Caenorhabditis elegans

Background: Among the four RecQ homologues predicted from the Caenorhabditis elegans genomic DNA sequence, T04A11.6 is most similar to Bloom syndrome's protein in humans. To investigate a possible interaction of the protein with topoisomerase IIIα (TOP3α), as observed between TOP3 and RecQ homologues in yeast and human, the top3α gene expression was suppressed by RNA interference (RNAi) in the him-6(e1104) C. elegans strain which is mutated in T04A11.6 (F. Mueller & C. Wicky, personal communication). Results: Germ cells in the gonads of the progeny him-6(e1104);top3α(RNAi) showed severe chromosomal abnormalities and were arrested during mitosis with a subsequent failure in meiotic entry. Most of the aberrant chromosomes were stained by the TUNEL assay but not by the SYTO12 dye, suggesting extensive DNA breaks not associated with apoptosis. The phenotypes in the germ cells of him-6(e1104);top3α(RNAi) were also observed in the progeny produced by double RNA interference of the top3α and him-6 gene expression, though at a reduced level. The over-expressed TOP3α and Him-6 proteins showed specific physical interaction in vitro, in agreement with the genetic interaction in C. elegans. Conclusion: In C. elegans, TOP3α and the RecQ homologue (T04A11.6) contribute to genome stability during germ-line mitosis, probably by acting in a complex.