EGO-1, a C. elegans RdRP, modulates gene expression via production of mRNA-templated short antisense RNAs.

The development of the germline in Caenorhabditis elegans is a complex process involving the regulation of thousands of genes in a coordinated manner. Several genes required for small RNA biogenesis and function are among those required for the proper organization of the germline. EGO-1 is a putative RNA-directed RNA polymerase (RdRP) that is required for multiple aspects of C. elegans germline development and efficient RNA interference (RNAi) of germline-expressed genes. RdRPs have been proposed to act through a variety of mechanisms, including the posttranscriptional targeting of specific mRNAs, as well as through a direct interaction with chromatin. Despite extensive investigation, the molecular role of EGO-1 has remained enigmatic. Here we use high-throughput small RNA and messenger RNA sequencing to investigate EGO-1 function. We found that EGO-1 is required to produce a distinct pool of small RNAs antisense to a number of germline-expressed mRNAs through several developmental stages. These potential mRNA targets fall into distinct classes, including genes required for kinetochore and nuclear pore assembly, histone-modifying activities, and centromeric proteins. We also found several RNAi-related genes to be targets of EGO-1. Finally, we show a strong association between the loss of small RNAs and the rise of mRNA levels in ego-1(-) animals. Our data support the conclusion that EGO-1 produces triphosphorylated small RNAs derived from mRNA templates and that these small RNAs modulate gene expression through the targeting of their cognate mRNAs.