title: Learning to protect your genome on the fly.
abstract: Piwi-interacting RNAs (piRNAs) help defend host genomes against germline transposons. In this issue of Cell, Khurana et al. show how alterations in the piRNA-encoding loci within a single generation allow a naive fly genome to overcome the initially insurmountable challenge imposed by a newly encountered mobile element.
authors.affiliation: Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.
authors.forename: Mia T
authors.initials: MT
authors.lastname: Levine
authors.forename: Harmit S
authors.initials: HS
authors.lastname: Malik