Focus on RNA interference A user’s guide

NA interference (RNAi) has exploded into a popular field CONTENTS methods of study and a major biology tool—both evolving very 670 On the art of rapidly. The idea of this user guide came from conversa- R identifying effective tions with researchers, which revealed that those interested in and specific siRNAs the tool face a confusing mass of literature from which it may Yi Pei & Thomas Tuschl .com/nature e be difficult to extract information about the state-of-the-art 677 Enhancing and reagents and practices. We have asked users, would-be users and confirming the

.natur specificity of RNAi w tool developers to help us identify the most common questions experiments Of RNAi and petunias. Artistic surrounding the use of RNAi. This Focus issue does not aim to Bryan R Cullen interpretation by Erin Boyle. be comprehensive, but tries to address these specific questions 682 Tuning silence: http://ww

within the context of mammalian systems. conditional systems The dsRNAs that trigger specific silencing by RNAi in mamma- for RNA interference oup r Maciej Wiznerowicz,

G lian cells come in many flavors: synthetic small interfering Jolanta Szulc & (siRNAs), their enzymatically produced cousins (esiRNAs), and Didier Trono short hairpin RNAs (shRNAs), which can be within several types of 689 Expressing short lishing b expression cassettes. This Focus touches on all of these and is divided hairpin RNAs in vivo Pu

into two sections. The first section contains four Perspectives Ola Snøve Jr & John J Rossi intended for researchers wishing to knock down the expression of 696 Enzymatically prepared RNAi libraries their favorite . The second section will be of interest to those Nature

Frank Buchholz, Ralf 6 wishing to embark on functional genomic screens. Kittler, Mikolaj Slabicki &

200 This second section is dedicated to RNAi libraries, which can Mirko Theis © be prepared enzymatically (as reviewed on p. 696) or purchased 701 shRNA libraries and as shRNA-expressing viral vectors. Several major shRNA libraries their use in cancer are now available, and they cover most human and mouse . René Bernards, To provide a comparative analysis of these resources, we present Thijn R Brummelkamp & Perspectives by their developers (p. 701, 707 and 715). Each article Roderick L Beijersbergen details a library’s performance, rationale of design and examples of 707 Lessons from Nature: application, and also contains a Box synthesizing this information microRNA-based for comparison at a glance. shRNA libraries We invite you to visit our Focus website, which features a collec- Kenneth Chang, Stephen J Elledge & tion of relevant papers published in Nature titles within the past Gregory J Hannon year, as well as a few ‘classics’. We are indebted to all those who 715 Genome-scale loss- provided input on this Focus and helped define its scope, and to of-function screening our authors and reviewers who generously put a lot of effort into with a lentiviral RNAi making this Focus a practical and useful reference. library David E Root, Nir Veronique Kiermer Hacohen, William C Hahn, Eric S Lander & David M Sabatini

Focus Editor Veronique Kiermer Senior Production Editor Copy Editor Irene Kaganman Focus Associate Editor Nicole Rusk Ingrid McNamara Design Erin Boyle Production Editors Brandy Moyer, Marketing Eric Claiborne Blake Dennis

NATURE METHODS | VOL.3 NO.9 | SEPTEMBER 2006 | 669