Review Exploring RNAi as a therapeutic strategy for controlling disease in aquaculture Paula C. Lima a, b, c , James O. Harris b, c , Mathew Cook a, c, * a CSIRO Marine and Atmospheric Research, C/- CSIRO Livestock Industries, QBP, 306 Carmody Rd, St Lucia, QLD 4067, Australia b School of Biological Sciences, Flinders University, GPO 2100, SA 5001, Australia c Seafood CRC, Science Park, Laffer Drive, Bedford Park, SA 5042, Australia article info Article history: Received 29 June 2012 Received in revised form 21 November 2012 Accepted 30 November 2012 Available online 28 December 2012 Keywords: RNA interference Aquaculture Gene function Infectious diseases abstract Aquatic animal diseases are one of the most significant constraints to the development and management of aquaculture worldwide. As a result, measures to combat diseases of fish and shellfish have assumed a high priority in many aquaculture-producing countries. RNA interference (RNAi), a natural mechanism for post-transcriptional silencing of homologous genes by double-stranded RNA (dsRNA), has emerged as a powerful tool not only to investigate the function of specific genes, but also to suppress infection or replication of many pathogens that cause severe economic losses in aquaculture. However, despite the enormous potential as a novel therapeutical approach, many obstacles must still be overcome before RNAi therapy finds practical application in aquaculture, largely due to the potential for off-target effects and the difficulties in providing safe and effective delivery of RNAi molecules in vivo. In the present review, we discuss the current knowledge of RNAi as an experimental tool, as well as the concerns and challenges ahead for the application of such technology to combat infectious disease of farmed aquatic animals. Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. 1. Introduction Aquaculture has expanded rapidly to become a major economic and food-producing sector in the world [1]. In parallel, due to the intensification of rearing methods and systems, the industry has been overwhelmed with a number of trans-boundary aquatic animal diseases caused by viruses, bacteria, fungi and parasites, with newer pathogens being identified every year [2]. Conse- quently, disease outbreaks have become a significant constraint to the development of the aquaculture industry, affecting the socio- economic development of this sector worldwide [3]. Therefore, in order to meet the increased demands of our expanding population, new technologies and techniques for disease control must be developed and implemented. Of major interest is the application of genetic engineering and other biotechnologies. One recent technology likely to play a major role in the future of aquaculture is RNA interference (RNAi). RNAi is a recently- discovered mechanism of post-transcriptional gene silencing in which double-stranded RNA (dsRNA) corresponding to a gene, or coding region, of interest is introduced into an organism, resulting in degradation of the corresponding mRNA [4]. Because of this sequence-specific ability to silence target genes, RNAi has been extensively used to investigate the functional role of specific genes by reducing expression, without altering genotypes [5]. The silencing effects could be used not only to study gene function, but also to indentify drug targets and vaccine candidates [6], as well as to control infectious disease by interfering with pathogen trans- mission, development and proliferation within the host [5]. In this review we summarize the current knowledge regarding the therapeutic applications of RNAi for developing alternative treatment strategies against infectious diseases in aquaculture. 2. RNA interference RNA interference (RNAi) is a highly evolutionally conserved process of post-transcriptional gene silencing (PTGS) by which double-stranded RNA (dsRNA), when introduced into a cell, causes sequence-specific degradation of homologous mRNA sequences [7]. RNAi as a mechanism of PTGS most likely evolved as a cellular defence strategy to eliminate unwanted nucleic acids (viruses and transposable elements) in plants, fungus and invertebrates [8], but * Corresponding author. CSIRO Marine and Atmospheric Research, C/- CSIRO Livestock Industries, QBP, 306 Carmody Rd, StLucia, QLD 4067, Australia. Tel.: þ61 7 3214 2317; fax: þ61 7 3214 2430. E-mail address: mathew.cook@csiro.au (M. Cook). Contents lists available at SciVerse ScienceDirect Fish & Shellfish Immunology journal homepage: www.elsevier.com/locate/fsi 1050-4648/$ e see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fsi.2012.11.037 Fish & Shellfish Immunology 34 (2013) 729e743