title: Drosophila Piwi functions downstream of piRNA production mediating a chromatin-based transposon silencing mechanism in female germ line.
abstract: Transposon control is a critical process during reproduction. The PIWI family proteins can play a key role, using a piRNA-mediated slicing mechanism to suppress transposon activity posttranscriptionally. In Drosophila melanogaster, Piwi is predominantly localized in the nucleus and has been implicated in heterochromatin formation. Here, we use female germ-line-specific depletion to study Piwi function. This depletion of Piwi leads to infertility and to axis specification defects in the developing egg chambers; correspondingly, widespread loss of transposon silencing is observed. Germ-line Piwi does not appear to be required for piRNA production. Instead, Piwi requires Aubergine (and presumably secondary piRNA) for proper localization. A subset of transposons that show significant overexpression in germ-line Piwi-depleted ovaries exhibit a corresponding loss of HP1a and H3K9me2. Germ-line HP1a depletion also leads to a loss of transposon silencing, demonstrating the functional requirement for HP1a enrichment at these loci. Considering our results and those of others, we infer that germ-line Piwi functions downstream of piRNA production to promote silencing of some transposons via recruitment of HP1a. Thus, in addition to its better-known function in posttranscriptional silencing, piRNA also appears to function in a targeting mechanism for heterochromatin formation mediated by Piwi.
authors.affiliation: Department of Biology, Washington University in St. Louis, St Louis, MO 63130, USA.
authors.forename: Sidney H
authors.initials: SH
authors.lastname: Wang
authors.forename: Sarah C R
authors.initials: SC
authors.lastname: Elgin
mesh_terms: D000818:Animals; D060565:Argonaute Proteins / Q000378:metabolism / Q000502:physiology*; D015152:Blotting, Northern; D015153:Blotting, Western; D047369:Chromatin Immunoprecipitation; D000090266:Chromobox Protein Homolog 5; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004251:DNA Transposable Elements / Q000235:genetics*; D029721:Drosophila Proteins / Q000378:metabolism / Q000502:physiology*; D004331:Drosophila melanogaster / Q000235:genetics / Q000502:physiology*; D005260:Female; D005854:Germ Cells / Q000378:metabolism*; D006570:Heterochromatin / Q000378:metabolism / Q000502:physiology*; D018613:Microscopy, Confocal; D034622:RNA Interference / Q000502:physiology*; D034741:RNA, Small Interfering / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D060565:Argonaute Proteins; D002868:Chromosomal Proteins, Non-Histone; D017931:DNA Primers; D004251:DNA Transposable Elements; D029721:Drosophila Proteins; D006570:Heterochromatin; D034741:RNA, Small Interfering; C116498:piwi protein, Drosophila; D000090266:Chromobox Protein Homolog 5