title: Increased production of piRNAs from euchromatic clusters and genes in Anopheles gambiae compared with Drosophila melanogaster.
abstract: BACKGROUND
  Specific genomic loci, termed Piwi-interacting RNA (piRNA) clusters, manufacture piRNAs that serve as guides for the inactivation of complementary transposable elements (TEs). The piRNA pathway has been accurately detailed in Drosophila melanogaster, while it remains poorly examined in other insects. This pathway is increasingly recognized as critical for germline development and reproduction. Understanding of the piRNA functions in mosquitoes could offer an opportunity for disease vector control by the reduction of their reproductive potential.
  
  
  RESULTS
  To analyze the similarities and differences in this pathway between Drosophila and mosquito, we performed an in-depth analysis of the genomic loci producing piRNAs and their targets in the African malaria vector Anopheles gambiae. We identified 187 piRNA clusters in the An. gambiae genome and 155 piRNA clusters in the D. melanogaster genome. We demonstrate that many more piRNA clusters in the mosquito compared with the fruit fly are uni-directionally transcribed and are located outside pericentromeric heterochromatin. About 11 % of the An. gambiae piRNA population map to gene transcripts. This is a noticeable increase compared with the ~6 % of the piRNA population mapped to genes in D. melanogaster. A subset of the piRNA-enriched genes in An. gambiae has functions related to reproduction and development. At least 24 and 65 % of the mapped piRNAs correspond to genomic TE sequences in An. gambiae and D. melanogaster, respectively. DNA transposons and non-LTR retrotransposons are more abundant in An. gambiae, while LTR retrotransposons are more abundant in D. melanogaster. Yet, piRNAs predominantly target LTR retrotransposons in both species, which may point to a distinct feature of these elements compared to the other classes of TEs concerning their silencing by the piRNA pathway.
  
  
  CONCLUSIONS
  Here, we demonstrate that piRNA-producing loci have more ubiquitous distribution in the An. gambiae genome than in the genome of D. melanogaster. Also, protein-coding genes have an increased role in production of piRNAs in the germline of this mosquito. Genes involved in germline and embryonic development of An. gambiae generate a substantial portion of piRNAs, suggesting a role of the piRNA pathway in the epigenetic regulation of the reproductive processes in the African malaria vector.
authors.affiliation: Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA.
authors.forename: Phillip
authors.initials: P
authors.lastname: George
authors.affiliation: Laboratoire Génétique, Reproduction, et Développement, Clermont Université, Université d'Auvergne, BP 38, 63001 Clermont-Ferrand, France.|Institut National de la Santé et de la Recherche Médicale, U 1103, BP 38, 63001 Clermont-Ferrand, France.|Centre National de Recherche Scientifique, UMR 6293, BP 38, 63001 Clermont-Ferrand, France.
authors.forename: Silke
authors.initials: S
authors.lastname: Jensen
authors.affiliation: Laboratoire Génétique, Reproduction, et Développement, Clermont Université, Université d'Auvergne, BP 38, 63001 Clermont-Ferrand, France.|Institut National de la Santé et de la Recherche Médicale, U 1103, BP 38, 63001 Clermont-Ferrand, France.|Centre National de Recherche Scientifique, UMR 6293, BP 38, 63001 Clermont-Ferrand, France.
authors.forename: Romain
authors.initials: R
authors.lastname: Pogorelcnik
authors.affiliation: The PhD Program in Genomics Bioinformatics and Computational Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA.
authors.forename: Jiyoung
authors.initials: J
authors.lastname: Lee
authors.affiliation: The PhD Program in Genomics Bioinformatics and Computational Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Xing
authors.affiliation: Laboratoire Génétique, Reproduction, et Développement, Clermont Université, Université d'Auvergne, BP 38, 63001 Clermont-Ferrand, France.|Institut National de la Santé et de la Recherche Médicale, U 1103, BP 38, 63001 Clermont-Ferrand, France.|Centre National de Recherche Scientifique, UMR 6293, BP 38, 63001 Clermont-Ferrand, France.
authors.forename: Emilie
authors.initials: E
authors.lastname: Brasset
authors.affiliation: Laboratoire Génétique, Reproduction, et Développement, Clermont Université, Université d'Auvergne, BP 38, 63001 Clermont-Ferrand, France.|Institut National de la Santé et de la Recherche Médicale, U 1103, BP 38, 63001 Clermont-Ferrand, France.|Centre National de Recherche Scientifique, UMR 6293, BP 38, 63001 Clermont-Ferrand, France.
authors.forename: Chantal
authors.initials: C
authors.lastname: Vaury
authors.affiliation: Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA.|The PhD Program in Genomics Bioinformatics and Computational Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA.
authors.forename: Igor V
authors.initials: IV
authors.lastname: Sharakhov
keywords: Anopheles gambiae; Development; Drosophila melanogaster; Euchromatin; Germline; Heterochromatin; Reproduction; Small RNAs; Transposable element; piRNA clusters