AbstractsBiology & Animal Science

Insects rely largely on the sense of smell for reproduction and survival. Drosophila flies detect volatile environmental cues with arrays of olfactory receptor neurons (ORNs) housed in specialized hairs, called sensilla, covering the antennae and maxillary palps. Three olfactory receptor protein families, Ors, Grs and IRs, underlie the responses of ORNs to odorants. In order to isolate novel components involved in ORN responses, two genetic screens had been performed prior to this project. Fly strains carrying mutagenized chromosomes were screened for defects in odor-evoked ORN response, using the electropalpogram (EPG) and electroantennogram (EAG) techniques which are electrophysiological responses derived from receptor potentials. Each screen isolated one mutant strain that showed greatly reduced EPG and EAG amplitudes. To determine the molecular lesion causing the mutant phenotypes, phenotypic characterization, genetic mapping, genomic sequencing and loss-of-function studies on individual candidate genes were performed. A P4-ATPase phospholipid transporter, dATP8B, was identified as the cause of one mutant phenotype, and is crucial for the sensitivity of Or- expressing ORNs. The requirement is highly specific, as ORN responses mediated by Gr and IR proteins are not affected in the mutant strain. Characterizations of odor-evoked responses, Or localization, and action potential amplitudes in dATP8B mutant animals suggest that dATP8B plays a role in Or-signaling as well as in spike generation. While the identification of the phenotype-causing mutation was not successful in the second mutant strain, analysis of olfactory electrical signals recorded from the mutant as well as wild type animals revealed interesting electrical properties of the olfactory epithelium. Firstly, neighboring sensilla were shown to be electrically coupled in wild type animals. Furthermore, the data suggest that rather than impairing ORN functions, the mutation affects the electrical properties of the olfactory epithelium, such that the coupling conductance between sensillum populations is reduced in the mutants. In summary, this thesis identified a new gene crucial for the sensitivity of Or-expressing ORNs and provided a preliminary characterization on the electrical properties of the olfactory epithelium in Drosophila.