Role of sja-let-7 in egg production and reproductive development in female Schistosoma japonicum.

Schistosoma japonicum, a parasitic flatworm, exhibits the special biological phenomenon of male-female pairing, essential for the reproductive maturation and egg production of female worms. MicroRNAs (miRNAs) are known to regulate female reproductive development, yet the roles of individual miRNAs in schistosome reproduction remain poorly defined. Among them, the conserved let-7 family, identified in S. japonicum as early as 2008, has not been explored for its specific biological functions. Expression profiling of sja-let-7 was first conducted across multiple datasets and validated through qPCR. Bioinformatic tools were used to predict sja-let-7 target genes, and fluorescence in situ hybridization (FISH) was employed to determine sja-let-7 localization in reproductive organs. Functional studies involving sja-let-7 modulation through mimics and inhibitors in vitro, and agomir and antagomir treatments in vivo, were conducted to evaluate its impact on female reproductive development, target gene regulation, and egg production. Results showed that sja-let-7 demonstrated prominent localization in the Mehlis' gland, ovaries, and vitellaria of female. Sjcdc23, a potential target gene of sja-let-7, was implicated to play a potential role in reproductive processes of schistosomes. Overexpression or inhibition of sja-let-7 significantly impaired egg production and quality in vitro. In vivo experiments demonstrated disrupted vitellaria development and reduced egg production in agomir-treated worms, while antagomir treatment also decreased egg production, suggesting that sja-let-7 is crucial for female reproductive development and egg-laying capacity, providing novel insights into miRNA-mediated regulatory mechanisms in parasitic helminths.