Maternal enhancement of cytotype regulation in Drosophila melanogaster by genetic interactions between telomeric P elements and non-telomeric transgenic P elements.

The X-linked telomeric P elements (TPs) TP5 and TP6 regulate the activity of the entire P element family because they are inserted in a major locus for the production of Piwi-interacting RNAs (piRNAs). The potential for this cytotype regulation is significantly strengthened when either TP5 or TP6 is combined with a non-telomeric X-linked or autosomal transgene that contains a P element. By themselves, none of the transgenic P elements have any regulatory ability. Synergism between the telomeric and transgenic P elements is much greater when the TP is derived from a female. Once an enhanced regulatory state is established in a female, it is transmitted to her offspring independently of either the telomeric or transgenic P elements - that is, it works through a strictly maternal effect. Synergistic regulation collapses when either the telomeric or the transgenic P element is removed from the maternal genotype, and it is significantly impaired when the TPs come from stocks heterozygous for mutations in the genes aubergine, piwi or Su(var)205. The synergism between telomeric and transgenic P elements is consistent with a model in which P piRNAs are amplified by alternating, or ping-pong, targeting of primary piRNAs to sense and antisense P transcripts, with the sense transcripts being derived from the transgenic P element and the antisense transcripts being derived from the TP.