piRNA-mediated nuclear accumulation of retrotransposon transcripts in the Drosophila female germline.
Germline silencing of transposable elements is essential for the maintenance of genome integrity. Recent results indicate that this repression is largely achieved through a RNA silencing pathway that involves Piwi-interacting RNAs (piRNAs). However the repressive mechanisms are not well understood. To address this question, we used the possibility to disrupt the repression of the Drosophila I element retrotransposon by hybrid dysgenesis. We show here that the repression of the functional I elements that are located in euchromatin requires proteins of the piRNA pathway, and that the amount of ovarian I element piRNAs correlates with the strength of the repression in the female germline. Antisense RNAs, which are likely used to produce antisense piRNAs, are transcribed by heterochromatic defective I elements, but efficient production of these antisense small RNAs requires the presence in the genome of euchromatic functional I elements. Finally, we demonstrate that the piRNA-induced silencing of the functional I elements is at least partially posttranscriptional. In a repressive background, these elements are still transcribed, but some of their sense transcripts are kept in nurse cell nuclear foci together with those of the Doc retrotransposon. In the absence of I element piRNAs, either in dysgenic females or in mutants of the piRNA silencing pathway, sense I element transcripts are transported toward the oocyte where retrotransposition occurs. Our results indicate that piRNAs are involved in a posttranscriptional gene-silencing mechanism resulting in RNA nuclear accumulation.
Chambeyron
Séverine
S
Institut de Génétique Humaine, Centre National de la Recherche Scientifique, 34396 Montpellier Cedex 5, France.
Popkova
Anna
A
Payen-Groschêne
Geneviève
G
Brun
Christine
C
Laouini
Dorsaf
D
Pelisson
Alain
A
Bucheton
Alain
A
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics*; D004331:Drosophila melanogaster / Q000235:genetics* / Q000378:metabolism; D005260:Female; D020868:Gene Silencing; D010063:Ovum / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000502:physiology*; D018626:Retroelements / Q000235:genetics*; D014158:Transcription, Genetic
D029721:Drosophila Proteins; C117553:I-element-gag protein, Drosophila; D034741:RNA, Small Interfering; D018626:Retroelements