Figure 7.
Two steps may be necessary to activate the host defense against an invading TE. According to the prevailing view, that is, the trap model, a TE insertion into a piRNA cluster is sufficient to trigger the host control over an invading TE. In our updated model, the two-step model, we propose that silencing of an invading TE requires two steps: (1) the generation of some first piRNAs and (2) the initiation of the ping-pong cycle. Yellow flashes indicate necessary events for establishing the host control.
