The RNAi pathway represses the transposition of Tc1 element in the germ line by targeting the transposase mRNA for degradation.
Tc1 transposes in somatic cells because RNAi is not sufficient and some transposase can be produced. If transposition of Tc1 is no longer repressed in germ line, the element will transpose during the production of gametes in C. elegans. This will cause the insertion of Tc1 element into genes and resulting in mutations.
The RNAi silencing pathway is akin to radar in that the host is able to detect new insertions into the genome. The host can then respond by silencing the transposase gene and thus prevent the movement of all the family members.
Over the past decade the researchers have discovered that mutations that disrupt the RNAi pathway often lead to the activation of transposable elements in their respective genomes.