Ectopic expression of multi-transgenic copies can result in reduced expression of the transgene and can induce silence of endogenous gene; this process is called as co-suppression. Using a transgene-mediated co-suppression technique, we demonstrated the biological function of DNA topoisomerase-1 (
top-1) in C. elegans development. Introduction of full-length
top-1 transgene sufficiently induced the co-suppression of endogenous
top-1 gene, causing embryonic lethality and abnormal germline development. We also found that the co-suppression of
top-1 gene affected morphogenesis, lifespan and larval growth that were not observed in
top-1 (RNAi) animals. Strikingly, co-suppression effects were significantly reduced by the elimination of
top-1 introns, suggesting that efficient co-suppression may require intron(s) in C. elegans. Sequence analysis revealed that the introns 1 and 2 of
top-1 gene possess consensus binding sites for several transcription factors, including MAB-3, LIN-14, TTX-3/CEH-10, CEH-1, and CEH-22. Among them, we examined a genetic link between
ceh-22 and
top-1. The
ceh-22 is partially required for the specification of distal tip cells (DTC), which functions as a stem cell niche in the C. elegans gonad. Intriguingly,
top-1 (RNAi) significantly enhanced DTC loss in
ceh-22 mutant gonads, indicating that
top-1 may play an important role in CEH-22-mediated DTC fate specification. Therefore, our findings suggest that transgene-mediated co-suppression facilitates the silencing of the specific genes and the study of gene function in vivo.