Figure 1.
In C. elegans, piRNAs are transcribed by RNA Polymerase II (Pol II) and primary siRNAs can be produced from exogenous dsRNA. piRNAs and primary siRNAs are stabilized by unique Argonaute proteins (yellow) and can direct the production of highly amplified secondary siRNAs by RNA-directed RNA polymerases (RdRPs). Secondary siRNAs bound to the Argonaute HRDE-1 can direct transcriptional and post-transcriptional silencing of homologous loci. HRDE-1 is required for the heritable transmission of gene regulatory information in C. elegans.