title: Function of Piwi, a nuclear Piwi/Argonaute protein, is independent of its slicer activity.
abstract: The Piwi protein subfamily is essential for Piwi-interacting RNA (piRNA) biogenesis, transposon silencing, and germ-line development, all of which have been proposed to require Piwi endonuclease activity, as validated for two cytoplasmic Piwi proteins in mice. However, recent evidence has led to questioning of the generality of this mechanism for the Piwi members that reside in the nucleus. Drosophila offers a distinct opportunity to study the function of nuclear Piwi proteins because, among three Drosophila Piwi proteins--called Piwi, Aubergine, and Argonaute 3--Piwi is the only member of this subfamily that is localized in the nucleus and expressed in both germ-line and somatic cells in the gonad, where it is responsible for piRNA biogenesis and regulatory functions essential for fertility. In this study, we demonstrate beyond doubt that the slicer activity of Piwi is not required for any known functions in vivo. We show that, in transgenic flies with the DDX catalytic triad of PIWI mutated, neither primary nor secondary piRNA biogenesis is detectably affected, transposons remain repressed, and fertility is normal. Our observations demonstrate that the mechanism of Piwi is independent of its in vitro endonuclease activity. Instead, it is consistent with the alternative mode of Piwi function as a molecule involved in the piRNA-directed guidance of epigenetic factors to chromatin.
authors.affiliation: Yale Stem Cell Center and Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06509, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Darricarrère
authors.forename: Na
authors.initials: N
authors.lastname: Liu
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Watanabe
authors.forename: Haifan
authors.initials: H
authors.lastname: Lin
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D060565:Argonaute Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D004251:DNA Transposable Elements / Q000235:genetics; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics / Q000378:metabolism; D005260:Female; D008297:Male; D008957:Models, Genetic; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009866:Oogenesis / Q000235:genetics; D055550:Protein Stability; D034741:RNA, Small Interfering / Q000096:biosynthesis / Q000235:genetics
chemical_list: D060565:Argonaute Proteins; D004251:DNA Transposable Elements; D029721:Drosophila Proteins; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; C116498:piwi protein, Drosophila