Peri-centrosomal localization of small interfering RNAs in C. elegans

The centrosome serves as the microtubule-organizing center and plays a critical role in cell division. Centrosomal RNAs (cnRNAs) have been reported to enable precise spatiotemporal control of gene expression during cell division in many species. However, whether and how cnRNAs exist in C. elegans and, if yes, their functions and mechanisms remain unclear.

A recent study published in SCIENCE CHINA Life Sciences reported that using the nuclear RNAi Argonaute protein NRDE-3 as a reporter, researchers identified potential peri-centrosome-localized small interfering (si)RNAs in C. elegans. The findings provide new insights that the peri-centrosomal region may function as a platform for RNAi-mediated gene regulation.

NRDE-3 is an Argonaute protein that can bind to siRNAs and then associate with targeted RNAs containing complementary nucleic acids sequences of the siRNAs. Upon binding to siRNAs, NRDE-3 usually translocates to the nucleus and associates with targeted pre-mRNAs, or to the nucleoli and associates with pre-rRNA in the presence of risiRNAs. Therefore, NRDE-3 can be used to represent the subcellular localization of siRNAs and their target RNAs. By using CRISPR/Cas9 technology, researchers generated a GFP-tagged NRDE-3 knock-in transgene as the reporter. NRDE-3 was expressed in oocytes, early and late embryos, and somatic cells and was enriched in the nucleus. Its nuclear localization depends on the presence of 22G siRNAs synthesized by RNA-dependent RNA polymerases (RdRPs).

Strikingly, in certain mutants of small RNA pathway factors (e.g., eri-1, ergo-1, or drh-3), researchers found that NRDE-3 accumulates in the peri-centrosomal foci in embryos. NRDE-3 foci neighbored the centriole proteins and pericentriolar material (PCM) components in embryos. The peri-centrosomal accumulation of NRDE-3 also depends on the RNA-dependent RNA polymerase (RdRP)-synthesized 22G siRNAs and the PAZ domain of NRDE-3, which is essential for siRNA binding. Furthermore, NRDE-3 accumulated at centrosome in a cell cycle-dependent manner. In metaphase, NRDE-3 is enriched at the peri-centrosomal region and spindle during metaphase. Moreover, the integrity of centriole proteins and pericentriolar material (PCM) components is also required for the peri-centrosomal accumulation of NRDE-3. Functional studies further revealed that peri-centrosomal accumulation of NRDE-3 is important for C. elegans development. Finally, the researchers identified the peri-centrosome-enriched siRNAs, which predominantly mapped to the 3’ portion of the target genes.

This study represents a first step in characterizing potential peri-centrosome-localized siRNAs. Further studies are needed to explore the mechanisms and functions underlying the peri-centrosomal accumulation of Ago/siRNAs complex. Moreover, the subcellular localization of NRDE-3 may be used to track the dynamics and transport of RNAs in distinct subcellular organelles.

This research was collaboratively conducted by Qile Jin, Ph.D. student at the University of Science and Technology of China (USTC), and Dr. Xuezhu Feng from Anhui Medical University. Drs. Chengming Zhu, Shouhong Guang, and Xinya Huang from USTC, are the corresponding authors of the work. This study was supported by grants from the National Natural Science Foundation of China, the Ministry of Science and Technology, the Institute of Health and Medicine, Hefei comprehensive National Science Center, and USTC.

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