title: Homology-dependent silencing by an exogenous sequence in the Drosophila germline.
abstract: The study of P transposable element repression in Drosophila melanogaster led to the discovery of the trans-silencing effect (TSE), a homology-dependent repression mechanism by which a P-transgene inserted in subtelomeric heterochromatin (Telomeric Associated Sequences) represses in trans, in the female germline, a homologous P-lacZ transgene inserted in euchromatin. TSE shows variegation in ovaries and displays a maternal effect as well as epigenetic transmission through meiosis. In addition, TSE is highly sensitive to mutations affecting heterochromatin components (including HP1) and the Piwi-interacting RNA silencing pathway (piRNA), a homology-dependent silencing mechanism that functions in the germline. TSE appears thus to involve the piRNA-based silencing proposed to play a major role in P repression. Under this hypothesis, TSE may also be established when homology between the telomeric and target loci involves sequences other than P elements, including sequences exogenous to the D. melanogaster genome. We have tested whether TSE can be induced via lacZ sequence homology. We generated a piggyBac-otu-lacZ transgene in which lacZ is under the control of the germline ovarian tumor promoter, resulting in strong expression in nurse cells and the oocyte. We show that all piggyBac-otu-lacZ transgene insertions are strongly repressed by maternally inherited telomeric P-lacZ transgenes. This repression shows variegation between egg chambers when it is incomplete and presents a maternal effect, two of the signatures of TSE. Finally, this repression is sensitive to mutations affecting aubergine, a key player of the piRNA pathway. These data show that TSE can occur when silencer and target loci share solely a sequence exogenous to the D. melanogaster genome. This functionally supports the hypothesis that TSE represents a general repression mechanism which can be co-opted by new transposable elements to regulate their activity after a transfer to the D. melanogaster genome.
authors.affiliation: Laboratoire Biologie du Développement, UMR7622, CNRS-Université Pierre et Marie Curie, 9 quai Saint-Bernard, 75005 Paris, France.
authors.forename: Maria
authors.initials: M
authors.lastname: Pöyhönen
authors.forename: Augustin
authors.initials: A
authors.lastname: de Vanssay
authors.forename: Valérie
authors.initials: V
authors.lastname: Delmarre
authors.forename: Catherine
authors.initials: C
authors.lastname: Hermant
authors.forename: Anne Laure
authors.initials: AL
authors.lastname: Todeschini
authors.forename: Laure
authors.initials: L
authors.lastname: Teysset
authors.forename: Stéphane
authors.initials: S
authors.lastname: Ronsseray