The IDR-containing protein PID-2 affects Z granules and is required for piRNA-induced silencing in the embryo

Abstract

In Caenorhabditis elegans, the piRNA (21U RNA) pathway is required to establish proper gene regulation and an immortal germline. To achieve this, PRG-1-bound 21U RNAs trigger silencing mechanisms mediated by RNA-dependent RNA polymerase (RdRP)-synthetized 22G RNAs. This 25 silencing can become PRG-1-independent, and heritable over many generations. This state is named RNAe. It is unknown how and when RNAe is established, and how it is maintained. We show that maternally provided 21U RNAs can be sufficient to trigger RNAe in embryos. Additionally, we identify the IDR-containing protein PID-2, as a factor required to establish and maintain RNAe. PID-2 interacts with two novel, partially redundant, eTudor domain proteins, PID-4 and PID-5. Additionally, PID-5 has 30 a domain related to the X-prolyl aminopeptidase protein APP-1, and binds APP-1, implicating Nterminal proteolysis in RNAe. All three proteins are required for germline immortality, localize to perinuclear foci, affect Z granules, and are required for balancing of 22G RNA populations. Overall, our study identifies three new proteins with crucial functions in the C. elegans small RNA silencing network. 35

Connecting the Dots: Linking Caenorhabditis elegans Small RNA Pathways and Germ Granules

“…ZNFX-1 contains an RNA helicase domain and a cysteine-rich zinc finger domain, while WAGO-4 is an Argonaute (AGO) protein that associates with the CSR-1 class of 22G-RNAs [2,3,27]. The intrinsically disordered region (IDR) containing protein PID-2, was recently identified as a Z granule component through a screen for defective Piwi-interacting RNA (piRNA) silencing [28]. While ZNFX-1 and WAGO-4 localize to Z granules, neither one is necessary for the assembly of Z granules.…”

“…Because of this, it should be noted that observations claiming that a phenotype is dependent on loss of P granules generally do not consider that Z granules are also affected. A mutation in the Z granule component PID-2 has been observed to affect only Z granules by making larger and fewer granules [28]. SIMR foci seem to form independently of the other three germ granules [4].…”