To understand the basis of smell perception by studying: a) molecular components involved in signal reception and transduction b) coding processes of the olfactory information c) modulation of this information by other sensorial inputs at the integration level
Research has been carried out in order to genetically decipher genes that participate in smell perception and processing. Drosophila is particularly suited to this task. Its smell recognition apparatus is of low complexity and the genes involved can be targeted by genetic means. Insertion of transposon constructs at random into the genome reveals enhancer elements that direct specific gene expression in neurons involved in smell perception and processing through the build in indicator gene lac z. Eventually, function of the concomitant genes is reduced or even destroyed by the insertion leading to an anosmic phenotype. Strains showing the desired x-gal straining for mutant and molecular analysis were selected.
About 1000 new lines with different transposon insertion loci have been raised. In 20 lines beta-galactosidase activity driven by the insertion site has revealed enhancer elements for expression in part of or all the olfactory hairs of the third antennal segment, the larval smell organ or for brain structures like the antennal lobes and the mushroom bodies. These lines are currently tested in behavioural paradigms for smell recognition.
We use the model system Drosophila to contribute to the understanding of the process of smell perception. Because of its relatively simple olfactory system consisting of only 1200 receptor neurons genetic methods have proven particularly useful in detecting olfactory genes that are not accessible through sequence similarity to other genes. We, therefore, employ genetic and molecular techniques to identify specific components of the system whose functional contribution to the odorant perception process can be measured in vivo either by physiological or behavioural tests. Our experimental approach can be devided in two parts: First, we dissect the organization of the olfactory system by introducing at random into the genome transposons that report on genes activated in cells or cell populations of the olfactory organ. The transposon insertion thus leads us into close proximity of genes that are specifically activated and are likely to act in the olfactory perception cascade. Transposon insertions might have hit and inactivated the olfactory gene and thereby reveal a mutant phenotype. If this is, however, not the case, a new genetically induced "jump out" in a high proportion gives rise to deletion of neighbouring genomic DNA. The phenotype of mutations induced either by transposon insertion or remobilization caused deletions is analysed in the second part of our approach. Here, we apply methods to measure the behavioural or electrophysiological response of the mutant animals. Behavioural paradigms are used to test the response to different odorants. Direct electrophysiological measurements are performed at the main olfactory organ of the adults, the third antennal segment, in response to different airborne chemicals. In this way one can uncover mutations affecting olfactory perception or transduction in primary olfactory neurons. Applying different odorants we can distinguish mutations that have an effect on specific receptors from those that influence the general transduction pathways.
Funding SchemeCON - Coordination of research actions