Genetic Dissection of Zebrafish Olfactory Circuitry Mediating Attractive Response to Amino Acids

Tetsuya Koide1, Nobuhiko Miyasaka1, Kozo Morimoto1, Koichi Kawakami2, and Yoshihiro Yoshihara1

Laboratory for Neurobiology of Synapse, RIKEN Brain Science Institute1
Division of Molecular and Developmental Biology, National Institute of Genetics2

  In teleost fishes, there are two major types of olfactory sensory neurons (OSNs) in the olfactory epithelium: microvillous and ciliated OSNs. It has been suggested that microvillous OSNs projecting axons to lateral glomeruli in the olfactory bulb (OB) mediate feeding behavior, whereas ciliated OSNs mainly targeting medial glomeruli mediate social behavior. However, the molecular, cellular, and neural-circuit mechanisms underlying such olfactory behaviors are not fully understood yet. In the present study, we introduced a Tol2 transposon-mediated gene trap method for genetic dissection of the zebrafish olfactory system. Three transgenic zebrafish lines (Tg1, Tg2, and Tg3) were established in which a transcriptional activator GAL4 is expressed in distinct subsets of OSNs. By crossing individual lines with the UAS-GFP reporter line, olfactory axons were fluorescently visualized which innervate some overlapping but mostly different glomeruli in the OB, respectively. In Tg3, GAL4 was expressed predominantly in microvillous OSNs innervating the lateral chain of glomeruli that has been proposed to be the feeding-related and amino acid-responsive region of the OB. To genetically elucidate the functional role of these microvillous OSNs in the feeding behavior, the targeted expression of tetanus toxin light chain (TeTxLC) for neural transmission blockade was achieved in the GAL4-expressing OSNs of Tg3 by crossing with the UAS-TeTxLC transgenic line. Silencing the microvillous OSNs by the GAL4-driven expression of TeTxLC in Tg3 resulted in a dramatic loss of attractive response to amino acids. These findings clearly demonstrate the functional significance of a selective neural circuitry originating from the trapped OSNs in the amino acid-mediated feeding behavior of the zebrafish.