Functions of the Vasa gene in Schistosoma japonicum as assessed by RNA interference

Vasa, an enzyme belonging to the helicase family, contributes to the regulation of reproductive system development in many species. Thus, we hypothesized that the Vasa3 gene may function in the reproductive system of the parasite Schistosoma japonicum (S. japonicum), which is a major causative agent of schistosomiasis. It is a severe disease globally affecting humans and animals. To test this hypothesis, we firstly conducted whole mount in situ hybridization analyses and found that the S. japonicum Vasa3 (SjVasa3) gene was expressed mainly in the reproductive organs. We then explored the reproductive functions of Vasa3 in S. japonicum using RNA interference (RNAi) techniques. Coupled schistosomes collected from mice 28 days post infection (dpi) were transfected three times with SjVasa3-specific small interfering RNA (siRNA) and cultured in vitro for up to 10 days. As measured by quantitative PCR (qPCR) and Western blot analysis, levels of SjVasa3 mRNA and protein in Vasa siRNA treated worms were significantly reduced compared with untreated and scrambled siRNA treated worms. Confocal laser scanning microscopy (CLSM) images showed markedly siRNA induced changes in the morphology of the reproductive organs, especially in the female ovary, vitellarium and the male testes. SjVasa3 gene silencing also significantly reduced egg production. These data demonstrate that SjVasa3 is essential in reproductive organ development and egg production in S. japonicum, and could be a potential target for developing novel compounds to treat schistosomiasis.