Cloning and Functional Characterization of Odorant Receptors Expressed in the Zebrafish Olfactory System

Abstract

A given olfactory sensory neuron (OSN) in the olfactory epithelium chooses to express only one odorant receptor (OR) from the OR gene repertoire. OSNs expressing the same receptor project axons to the same reproducibly positioned glomerulus in the olfactory bulb. As a consequence, specific odorants evoke distinctive patterns of glomerular activation in the bulb. The human odorant receptor repertoire contains 400 genes while the zebrafish repertoire contains approximately 143 genes. Our objective is to correlate the odorant specificity of each zebrafish OR with the associated glomerulus they target in the bulb. To achieve this we are cloning ORs into an expression vector which is then transfected into Hana3A cells. OR activation is monitored via a high‐throughput luciferase reporter assay in response to a large library of approximately 850 individual and defined odorants. In our first preliminary studies we have successfully cloned three ORs (111‐7, 111‐11, and 128‐5) and have identified specific candidate odorants that activate each of them. We subsequently cloned 9 more ORs into the expression vector for further analysis and characterization of odorant activation. The heterologous expression system was found to be suitable for matching odorants to zebrafish ORs. In future studies, we will seek to determine a functional relationship between odorant‐specific responses of the odorant receptors with the target locations within the bulb of the olfactory sensory neurons that express them.