Animals of all the genotypes schematically shown in this figure were tested for whether they express GFP after heat shocking adult animals (see Experimental Procedures), as a measure to assess viral silencing; dark animals do not express GFP after heat shock, green animals do. Numbers are shown for the most relevant genotypes. The X-linked FR1gfp transgene is present only when specifically indicated.
(A) Reconstitution of the RNAi machinery re-silences viral production.
(B) The antiviral RNA silencing can pass through the sperm and is independent of the presence of the viral template. Because the FR1gfp array is on the X chromosome, F1 males originating from the cross of male FR1gfp/0 (indicating hemizygosity); rde-1(−/−) with rde-1(−/−) hermaphrodites will not contain the array.
(C) Long-term silenced worms contain a non-chromosomally encoded dominant spreading signal. Crossed animals carry the same genotype in regard to the transgene and rde locus, yet one strain is long-term silenced, while the other has lost its ability to silence. The long-term silenced strain is able to silence the non-silent strain in trans. Viral silencing was always assessed by heat-shock treatment to induce the gfp-tagged viral transcript. If the FR1gfp transgene was not present in a strain, it is not shown in the genotype.