title: PIWI homologs mediate histone H4 mRNA localization to planarian chromatoid bodies.
abstract: The well-known regenerative abilities of planarian flatworms are attributed to a population of adult stem cells called neoblasts that proliferate and differentiate to produce all cell types. A characteristic feature of neoblasts is the presence of large cytoplasmic ribonucleoprotein granules named chromatoid bodies, the function of which has remained largely elusive. This study shows that histone mRNAs are a common component of chromatoid bodies. Our experiments also demonstrate that accumulation of histone mRNAs, which is typically restricted to the S phase of eukaryotic cells, is extended during the cell cycle of neoblasts. The planarian PIWI homologs SMEDWI-1 and SMEDWI-3 are required for proper localization of germinal histone H4 (gH4) mRNA to chromatoid bodies. The association between histone mRNA and chromatoid body components extends beyond gH4 mRNA, since transcripts of other core histone genes were also found in these structures. Additionally, piRNAs corresponding to loci of every core histone type have been identified. Altogether, this work provides evidence that links PIWI proteins and chromatoid bodies to histone mRNA regulation in planarian stem cells. The molecular similarities between neoblasts and undifferentiated cells of other organisms raise the possibility that PIWI proteins might also regulate histone mRNAs in stem cells and germ cells of other metazoans.
authors.affiliation: Department of Biological Sciences, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA Howard Hughes Medical Institute, Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601 S. Goodwin Ave., Urbana, IL 61801, USA labib.rouhana@wright.edu.
authors.forename: Labib
authors.initials: L
authors.lastname: Rouhana
authors.affiliation: Howard Hughes Medical Institute, Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601 S. Goodwin Ave., Urbana, IL 61801, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Weiss
authors.affiliation: Howard Hughes Medical Institute, Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601 S. Goodwin Ave., Urbana, IL 61801, USA.
authors.forename: Ryan S
authors.initials: RS
authors.lastname: King
authors.affiliation: Howard Hughes Medical Institute, Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, 601 S. Goodwin Ave., Urbana, IL 61801, USA.
authors.forename: Phillip A
authors.initials: PA
authors.lastname: Newmark
mesh_terms: D000818:Animals; D060565:Argonaute Proteins / Q000235:genetics / Q000378:metabolism*; D015152:Blotting, Northern; D001973:Bromodeoxyuridine; D003594:Cytoplasmic Granules / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006657:Histones / Q000235:genetics* / Q000378:metabolism; D017404:In Situ Hybridization, Fluorescence; D009841:Oligonucleotides / Q000235:genetics; D010932:Planarians / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D012330:RNA, Double-Stranded / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D060565:Argonaute Proteins; D006657:Histones; D009841:Oligonucleotides; D012330:RNA, Double-Stranded; D012333:RNA, Messenger; D001973:Bromodeoxyuridine
keywords: Chromatoid bodies; Histone SLBP; Neoblasts; PIWI; RNP granules; Stem cells