title: Identification and characterization of two novel classes of small RNAs in the mouse germline: retrotransposon-derived siRNAs in oocytes and germline small RNAs in testes.
abstract: Small RNAs ranging in size between 18 and 30 nucleotides (nt) are found in many organisms including yeasts, plants, and animals. Small RNAs are involved in the regulation of gene expression through translational repression, mRNA degradation, and chromatin modification. In mammals, microRNAs (miRNAs) are the only small RNAs that have been well characterized. Here, we have identified two novel classes of small RNAs in the mouse germline. One class consists of approximately 20- to 24-nt small interfering RNAs (siRNAs) from mouse oocytes, which are derived from retroelements including LINE, SINE, and LTR retrotransposons. Addition of retrotransposon-derived sequences to the 3' untranslated region (UTR) of a reporter mRNA destabilizes the mRNA significantly when injected into full-grown oocytes. These results suggest that retrotransposons are suppressed through the RNAi pathway in mouse oocytes. The other novel class of small RNAs is 26- to 30-nt germline small RNAs (gsRNAs) from testes. gsRNAs are expressed during spermatogenesis in a developmentally regulated manner, are mapped to the genome in clusters, and have strong strand bias. These features are reminiscent of Tetrahymena approximately 23- to 24-nt small RNAs and Caenorhabditis elegans X-cluster small RNAs. A conserved novel small RNA pathway may be present in diverse animals.
authors.affiliation: Laboratory of Reproductive Biology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan. toshwata@lab.nig.ac.jp
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Watanabe
authors.forename: Atsushi
authors.initials: A
authors.lastname: Takeda
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Tsukiyama
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Mise
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Okuno
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sasaki
authors.forename: Naojiro
authors.initials: N
authors.lastname: Minami
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Imai
mesh_terms: D020413:3' Untranslated Regions; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D005260:Female; D015723:Gene Library; D008297:Male; D051379:Mice; D009865:Oocytes / Q000502:physiology*; D012313:RNA / Q000145:classification / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D018626:Retroelements / Q000235:genetics*; D013091:Spermatogenesis / Q000235:genetics*; D013737:Testis / Q000502:physiology*
chemical_list: D020413:3' Untranslated Regions; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D018626:Retroelements; D012313:RNA