6606 Nucleic Acids Research, 2011, Vol. 39, No. 15 expression in somatic tissues tends to be localized to speciﬁc cell types. Thus, tissues containing low overall pilRNA amounts might still have high pilRNA concentra- tions in discrete cells. Presence of pilRNA in somatic tissues across a wide range of animal species, from ﬂies to macaques, indicates their potential functional signiﬁ- cance. Based on their sequence features and genomic origins, pilRNA closely resemble the germline piRNA from the corresponding species, rather than piRNA found in the ﬂy ovarian somatic cells. It is, therefore, con- ceivable that functions of pilRNA in somatic tissues are similar to functions of piRNA in the germline. Further studies are needed to explore the full scope of pilRNA in animal somatic tissues, their association with Piwi proteins, as well as the functional roles they play. SUPPLEMENTARY DATA Supplementary Data are available at NAR Online. ACKNOWLEDGEMENTS We thank Suzhou Drug Safety Evaluation and Research Center and C.Lian, H.Cai and X.Zheng in particular for providing the macaque samples; Professor Yong Liu and Dr Liu Yang for providing mouse pancreas and 832/3 cell line; W. Tang for enabling us to do LCM experiments; J. Dent for editing the manuscript; E. Lizano and F. Xue for assistance and all members of the Comparative Biology Group in Shanghai for helpful discussions and suggestions. FUNDING Funding for open access charge: Ministry of Science and Technology of the People’s Republic of China (grant numbers 2007CB947004 and 2006CB910700); Chinese Academy of Sciences (grant numbers KSCX2-YW-R-094 and KSCX2-YW-R-251); Shanghai Institutes for Biological Sciences (grant number 2008KIT104); Max Planck Society; Bundesministerum fuer Bildung und Forschung. Conﬂict of interest statement. None declared. REFERENCES 1. Brennecke,J., Aravin,A.A., Stark,A., Dus,M., Kellis,M., Sachidanandam,R. and Hannon,G.J. 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