The Experts Speak Views on Four Key Questions About Zebrafish Research Keith C. Cheng and members of the zebrafish community* Our 2004 ‘‘Experts Speak’’ commentary in- cluded a series of well-considered perspectives on the potential contributions of the zebrafish to biology and human health. It is fun to look back on those comments. Since that time, the use of morpholino knockdowns as a reverse genetic tool has become commonplace. Inser- tional mutagenesis with evolving retroviral and now, transposon-based tools, has made it much easier to clone genes found in mutant screens, though the relative strength of ENU mutagene- sis to detect phenotypically interesting muta- tions in essential genes remains. To challenge the ease of morpholino knock-downs in zeb- rafish, somatic cell knockdowns of mammalian cell culture cells with RNAi has now become commonplace. Broadly-applicable targeted en- gineering of animal genomes, including zebra- fish, looms tantalizingly on the horizon. Before Steve Ekker 0 s arrival as our new edi- tor, to take another ‘‘snap shot’’ of our moving field, I was asked to help find out what some senior members of the zebrafish community think about where we are, focusing on four ques- tions (and a ‘‘grab bag’’of questions). Most striking was the large increase in discussion of relevance of the zebrafish to humans, which validates past and future NIH support for zebrafish research. The answers we received are presented in alphabetical order by inves- tigator last name, with editorial changes in brackets. May these comments inspire an ever- clearer vision of how the zebrafish will contri- bute to our understanding of the living world. 1. What do you think are the most significant contributions the zebrafish (and other fish) has made to our understanding of basic biology and medicine that we did not already know from other invertebrate (Drosophila, C. elegans, yeast) and vertebrate (Xenopus, chicken, mouse) model systems? Why? Well, the first choice is in vitro or in vivo model. In vitro systems are in general more convenient and are also more favorable from a 3R** perspective, but of course lack the complexity of the in vivo’s. The latter spans from insects to primates and the choice of an optimal model involves a Jake Gittlen Cancer Research Foundation, Penn State College of Medicine, Hershey, Pennsylvania. *Participants: Peter Alestro ¨ m, Gerrit Begemann, Michael J. Carvan, III, Keith C. Cheng, Kathy and Phil Crosier, Stephen Ekker, Anna Huttenlocher, Koichi Kawakami, Gregory Kelly, Vladimir Korzh, Graham Lieschke, Marina Mione, Melody N. Neely, Stephan Neuhauss, and Nikolaus S. Trede. **Reference to the 3R Research Foundation Switzerland, dedicated to reduction, refinement, and replacement of animal experi- mentation. ZEBRAFISH Volume 5, Number 1, 2008 ª Mary Ann Liebert, Inc. DOI: 10.1089/zeb.2008.9996 9