Crosstalk between and developmental dynamics of <i>C. elegans</i> Argonaute proteins

Gene regulation via Argonaute-bound small RNAs is a broadly conserved mechanism, present in all domains of life. The nematode Caenorhabditis elegans expresses several worm-specific Argonautes (WAGOs), which interact with the small RNAs known as 22G-RNAs. These WAGOs have roles in gene regulation, transposon-defence as well as in viral control and experimentally induced RNA interference. Despite many studies, direct relationships between WAGO targeting, as defined by 22G-RNA sequences, and mRNA abundance are not clear. Also, the effects of developmental stage and WAGO-interconnectivity have been under-studied thus far. We studied these aspects for two germline-expressed WAGO proteins, WAGO-1 and WAGO-3. We show that WAGO-1 mostly affects 22G-RNA expression in gravid adult worms, while WAGO-3 predominantly affects 22G-RNA expression in embryos. Furthermore, we detect a link between WAGO-3 and the maternal 26G-RNA pathway governed by the Argonaute protein ERGO-1, and between WAGO-1 and the paternal 26G-RNA pathway governed by the Argonautes ALG-3/4. We also demonstrate that, globally speaking, loss of WAGO-1 or WAGO-3 does not result in upregulation of their target mRNAs, as defined by 22G-RNA complementarity. Finally, metagene analysis of 22G-RNA profiles suggests loss of one WAGO protein leads to shifts in WAGO 22G-RNA binding. Overall, we conclude that WAGO-1 and WAGO-3 are developmentally dynamic, are embedded in distinct regulatory networks, and that potential silencing of individual mRNAs by these WAGO proteins is hard to assess by simple loss-of-function studies.