Har-P, a Short P-Element Variant, Weaponizes P-Transposase to Severely Impact Drosophila Gonad Development

When Drosophila mothers lacking P-element-piRNAs (i.e. ISO1) mate with certain fathers harboring active P-elements (i.e. Harwich, Har), hybrid daughters suffer from gonadal dysgenesis (GD), where ovaries collapse from uncontrolled P-element transposition. To discover the P-element driving GD, we selected hybrid D. melanogaster lines with portions of Har DNA within the ISO1 genome. We generated HISR-D and HISR-N lines retaining or losing GD induction, respectively. Despite greatly-reduced numbers of P-elements, HISR-D lines produced as many P-element piRNAs as parental Har. In these lines, we discovered a highly-truncated P-element variant: “Har-P”, which mobilized de novo in all HISR lines. Crossing P-transposase with Har-Ps in HISR-N lines restored GD and revealed a paternal P-element-piRNA-directed imprint on Har-Ps to suppress lethal somatic transposition. Har-P may weaponize P-transposase during catastrophic transposition.