Abstract

To initiate a genetic analysis of olfactory development and function in the zebrafish, Danio rerio, we developed a behavioral genetic screen for mutations affecting the olfactory sensory system. First, we characterized olfactory responses of wild-type zebrafish to various odors. We found that 3-day-old juvenile zebrafish reacted to the amino acid L-cysteine with an aversive behavioral response. We isolated one mutant, laure (lre), which showed no aversive behavioral response to L-cysteine at 3 days of development, and carried out a preliminary characterization of this mutant's defects. We found that Ire mutant fish were also defective in their response to L-serine and L-alanine, but not to taurocholic acid, as young adults. In addition, Ire mutant fish had significantly fewer primary olfactory sensory neurons than normal, and the axons of these neurons did not form the characteristic axon termination pattern in the developing olfactory bulb. Nevertheless, the olfactory epithelium of lre mutant fish showed normal or near normal electrophysiological responses to several odorants. Our data suggest that the behavioral defects observed in the ire mutant result from the disruption of the developing olfactory sensory neurons and their axonal connections within the olfactory bulb. The isolation of the Ire mutant shows that our behavior-based screen represents a viable approach for carrying out a genetic dissection of olfactory behaviors in this vertebrate model system. (c) 2005 Wiley-Liss, Inc.