Molecular Cell:小RNA對線蟲生殖的調節作用

（封面圖片：線蟲Piwi蛋白PRG-1定位於生殖細胞和早期胚胎（背景所示）中的P顆粒處。儘管線蟲piRNA的功能還需要得到進一步研究闡明，但科學家已經證實Piwi/piRNA對於Tc3轉位子活動性的一種siRNA調節模塊（圖片中積木塊所示）很重要。）

在多細胞生物中，Piwi相關的Argonaute蛋白被認為與維持生殖細胞自我更新有關，並且和一類小型RNA—piRNA相互作用。Piwi蛋白對於果蠅、斑馬魚以及小鼠的生殖細胞正常發育是必需的。piRNA在基因組當中定位與眾不同，長度大約為24-30個核苷酸，在哺乳動物的睪丸中表達，並且在精子發育過程中起著重要的生理調節作用。

在2008年7月11日出版的《分子細胞》（Molecular Cell）中，兩個研究小組分別發表文章稱，他們發現一種被稱為21U-RNA的21核苷長度RNA事實上在秀麗隱杆線蟲（C. elegans）中屬於piRNA。

來自美國的Batista等科學家發表文章稱，他們發現21U-RNA在線蟲生殖細胞中表達，並且與線蟲的Piwi蛋白家族成員PRG-1相互作用。此外研究人員還發現，21U-RNA的聚集依賴於PRG-1的活性。PRG-1蛋白在整個發育過程中持續表達，該蛋白定位於線蟲的P顆粒處。儘管21U-RNA位點存在一個保守上遊調節序列基元（conserved upstream sequence motif），成熟的21U-RNA並不保守，並且在某些情況下會無法表現出直接調節其它表達序列的跡象。因此，以上發現證實21U-RNA是線蟲的piRNA，而且這類小RNA以及相應的Piwi Argonaute蛋白與溫度相關的生殖力維持相關。

在另一篇文章中，來自英國、德國和荷蘭的一組科學家則表示，他們同樣認為，之前發現的21U-RNA事實上就是線蟲的piRNA。此外，Piwi以及piRNA的表達僅限於雄性和雌性的生殖細胞，並且獨立於其它多種小RNA途徑中的蛋白，其中包括DCR-1。研究小組還發現，Piwi對於Tc3基因的沉默是必需的，但對於其它Tc/mariner DNA轉位子則並不重要。與野生型相比，Piwi變異型線蟲的生殖細胞中Tc3去除率增加了至少100倍。科學家證實Piwi在Tc3沉默中起到內生siRNA途徑上遊的作用。因此以上結果顯示，在piRNA和siRNA功能之間存在聯繫。（生物谷Bioon.com）

生物谷推薦原始出處：

Molecular Cell，Vol 31, 67-78, 11 July 2008，Pedro J. Batista, Craig C. Mello

PRG-1 and 21U-RNAs Interact to Form the piRNA Complex Required for Fertility in C. elegans

Pedro J. Batista,1,5,10 J. Graham Ruby,2,3,6,10 Julie M. Claycomb,1 Rosaria Chiang,2,3,6 Noah Fahlgren,7,8 Kristin D. Kasschau,7,8 Daniel A. Chaves,1 Weifeng Gu,1 Jessica J. Vasale,1 Shenghua Duan,1 Darryl Conte Jr.,1 Shujun Luo,9 Gary P. Schroth,9 James C. Carrington,7,8 David P. Bartel,2,3,6, and Craig C. Mello1,4,

1 Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
2 Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
3 Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
4 Howard Hughes Medical Institute, Worcester, MA 01605, USA
5 Gulbenkian PhD Programme in Biomedicine, Rua da Quinta Grande, 6, 2780-156, Oeiras, Portugal
6 Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA
7 Center for Gene Research and Biotechnology, Oregon State University, Corvallis, OR 97331, USA

8 Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA
9 Illumina, Inc., Hayward, CA 94545, USA

Summary

In metazoans, Piwi-related Argonaute proteins have been linked to germline maintenance, and to a class of germline-enriched small RNAs termed piRNAs. Here we show that an abundant class of 21 nucleotide small RNAs (21U-RNAs) are expressed in the C. elegans germline, interact with the C. elegans Piwi family member PRG-1, and depend on PRG-1 activity for their accumulation. The PRG-1 protein is expressed throughout development and localizes to nuage-like structures called P granules. Although 21U-RNA loci share a conserved upstream sequence motif, the mature 21U-RNAs are not conserved and, with few exceptions, fail to exhibit complementarity or evidence for direct regulation of other expressed sequences. Our findings demonstrate that 21U-RNAs are the piRNAs of C. elegans and link this class of small RNAs and their associated Piwi Argonaute to the maintenance of temperature-dependent fertility.

Molecular Cell，Vol 31, 79-90, 11 July 2008，Partha P. Das, Eric A. Miska

Piwi and piRNAs Act Upstream of an Endogenous siRNA Pathway to Suppress Tc3 Transposon Mobility in the Caenorhabditis elegans Germline

Partha P. Das,1,2,3 Marloes P. Bagijn,1,4 Leonard D. Goldstein,4,5,7 Julie R. Woolford,1,2 Nicolas J. Lehrbach,1,2 Alexandra Sapetschnig,1,2 Heeran R. Buhecha,1,2 Michael J. Gilchrist,1 Kevin L. Howe,5 Rory Stark,5 Nik Matthews,5 Eugene Berezikov,6 René F. Ketting,6 Simon Tavaré,4,5,7 and Eric A. Miska 1,2,

1 Wellcome Trust Cancer Research UK Gurdon Institute, University of Cambridge, The Henry Wellcome Building of Cancer and Developmental Biology, Tennis Court Road, Cambridge CB2 1QN, UK
2 Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, UK
3 PhD Program, Faculty of Biology, GZMB, Georg-August-Universität Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany
4 Department of Oncology, University of Cambridge, Hills Road, Cambridge CB2 2XZ, UK
5 Cancer Research UK, Cambridge Research Institute, Li Ka-Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
6 Hubrecht Institute, Uppsalalaan 8, 3584 CT, Utrecht, The Netherlands
7 Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA, UK

Summary

The Piwi proteins of the Argonaute superfamily are required for normal germline development in Drosophila, zebrafish, and mice and associate with 24–30 nucleotide RNAs termed piRNAs. We identify a class of 21 nucleotide RNAs, previously named 21U-RNAs, as the piRNAs of C. elegans. Piwi and piRNA expression is restricted to the male and female germline and independent of many proteins in other small-RNA pathways, including DCR-1. We show that Piwi is specifically required to silence Tc3, but not other Tc/mariner DNA transposons. Tc3 excision rates in the germline are increased at least 100-fold in piwi mutants as compared to wild-type. We find no evidence for a Ping-Pong model for piRNA amplification in C. elegans. Instead, we demonstrate that Piwi acts upstream of an endogenous siRNA pathway in Tc3 silencing. These data might suggest a link between piRNA and siRNA function.