Conditional Ablation of Neurones in Transgenic Mice Anthony R. Isles, 1,2† Dan Ma, 1,2† Chloe Milsom, 1,2 Michael J. Skynner, 1 * Wei Cui, 3 John Clark, 3 Eric B. Keverne, 2 Nicholas D. Allen 1 1 Laboratory of Cognitive and Developmental Neuroscience, Neurobiology Programme, The Babraham Institute, Babraham, Cambridge, CB2 4AT, United Kingdom 2 Sub-Department of Animal Behaviour, University of Cambridge, Madingley, CB3 8AA, United Kingdom 3 Department of Gene Expression and Development, Roslin Institute, Roslin, Midlothian, EH25 9PS, United Kingdom Received 3 October 2000; accepted 2 January 2001 ABSTRACT: Conditional targeted ablation of spe- cific cell populations in living transgenic animals is a very powerful strategy to determine cell functions in vivo. This approach would be of particular value to study the functions of distinct neuronal populations; however, the transgene of choice for conditional cell ablation studies in mice, the herpes simplex virus thy- midine kinase gene, cannot be used to ablate neurones as its principal mode of action relies on cell proliferation. Here we report that expression of the E.coli nitroreduc- tase gene (Ntr) and metabolism of the prodrug CB1954 (5-aziridin-1-yl-2-4-dinitrobenzamide) to its cytotoxic derivative can be used to conditionally and acutely ab- late specific neuronal populations in vivo. As proof of principal, we have ablated olfactory and vomeronasal receptor neurones by expressing Ntr under the control of the olfactory marker protein (OMP) gene promoter. We demonstrate that following CB1954 administration, ol- factory and vomeronasal receptor neurones expressing the transgene were selectively eliminated from the olfac- tory epithelium (OE), and projections to the olfactory bulb (OB) were lost. The functional efficacy of cell ab- lation was demonstrated using a highly sensitive behav- ioural test to show that ablated mice had lost the olfac- tory ability to discriminate distinct odors and were consequently rendered anosmic. Targeted expression of Ntr to specific neuronal populations using conventional transgenes, as described here, or by “knock-in” gene targeting using embryonic stem cells may be of signifi- cant value to address the functions of distinct neuronal populations in vivo. © 2001 John Wiley & Sons, Inc. J Neurobiol 47: 183–193, 2001 Keywords: ablation; neurone; transgenic; olfactory; con- ditional INTRODUCTION One of the classic strategies to study the in vivo functions of selected neuronal populations or distinct neuroanatomical structures is cell ablation. Cell abla- tion can be achieved using a variety of techniques, ranging from physical to pharmacological lesioning (Shah and Jay, 1993), however, such techniques re- main relatively crude. The greatest selectivity could be potentially achieved using a genetic approach by directing the expression of a transgene encoding a cytotoxin under the control of a neurone-specific pro- moter. Two types of toxin have been used in trans- genic mice, those that are constitutively toxic, such as diptheria toxin or ricin (Landel et al., 1988; Palmiter ² ARI and DM made similar contributors to this work. *Present address: Pfizer Global Research and Development, University of Cambridge Forvie Site, Cambridge, CB2 2QB, United Kingdom. Correspondence to: N.D. Allen (nick.allen@bbsrc.ac.uk). Contract grant sponsor: BBSRC (E.B.K., N.D.A., and A.R.I.). © 2001 John Wiley & Sons, Inc. 183