The introduction of double-stranded RNA into eukaryotic cells leads to homology-dependent gene silencing, a process termed RNAi. In nematodes and plants, RNAi initiated in one location can spread systemically to silence the targeted gene throughout the organism. Furthermore, in the nematode C. elegans, dsRNA present in the environment can be transported into animals to initiate RNAi, so-called environmental RNAi. To investigate how gene-specific information can be transported between cells Dr. Hunter performed a forward genetic screen to identify genes required for systemic RNAi. Dr. Hunter is now characterizing the proteins specified by these genes to understand how double-stranded RNA is transported between cells. Understanding how intercellular RNA transport is accomplished and regulated in C. elegans may provide insight into why this activity is important to C. elegans and how to accomplish this in mammals, which may have significant therapeutic applications. The initial analysis identified systemic RNAi defective (sid) mutations in five genes. Two of these genes have been cloned and characterized. sid-1 encodes an apparent channel that allows passive transport of dsRNA into cells. sid-2 encodes an intestine limited transmembrane protein required for environmental RNAi. Functional analysis of SID-2 indicates that it may be the receptor for uptake of double-stranded RNA from the environment. The first objective of this project is to complete the analysis of the three remaining mutants. The second objective is to repeat the mutant hunt, but broaden the selective criteria to identify additional genes that may have essential roles for viability or fertility or that have tissue specific roles in RNAi. The broader impacts resulting from these activities include the training of postdoctoral investigators, Ph.D. students, and undergraduate thesis students as well as the potential applications that may unfold from a deep understanding of how dsRNA is trafficked between cells and tissues.
