The olfactory system of the Fruit fly, Drosophila melanogaster

The fruit fly Drosophila melanogaster is a classic genetic model organism that has also been instrumental in many breakthroughs in the study of olfaction in later years. From a position of relative obscurity, Drosophila has recently become the king among insects in olfactory research, and one of the major model species among animals. There are several reasons for the rise of this seemingly insignificant insect to such an elevated position. In 1999 the complete genome sequence of Drosophila melanogaster was released, which allowed the identification of the first insect olfactory receptor genes through bioinformatic screens of DNA sequences. To this day, Drosophila remains one of very few insects, and indeed rather few organisms, to have its genomic sequence detemined. Access to its complete genome sequence and methods for genetic manipulation, in combination with electrophysiological recordings and optical imaging, makes Drosophila a very powerful tool to investigate the relationships between olfactory genes, the nervous system, and olfactory behaviour.

 

Olfactory stimuli, Perception, and Odour preferences in Drosophila

Although Drosophila has been used in many investigations of the olfactory system and odour-driven learning and memory, very little effort has gone into characterizing the physiology and behaviour towards natural odours that the fly normally utilizes, e.g. for oviposition in fermenting fruit. I am identifying ecologically relevant odours from natural odour sources by using the fly´s own olfactory system as a detector. Recordings from hyper-sensitive single olfactory receptor neurons stimulated with biological extracts fractionated in a gas chromatograph are used to pin-point active compounds. Behavioural experiments with biological extracts and synthetic stimuli are used to characterize the preference of different strains and species for specific odours.

 

Odours and Olfactory Receptor Genes in Related Drosophila species

The genus Drosophila comprises hundreds of related species with differing food and habitat specializations, from generalist exploiters of fermenting fruits to specialists breeding in only a single plant species. The olfactory sense of each species has presumably adapted to detect odours necessary for finding its specific substrates used for breeding. We want to identify olfactory host cues for several Drosophila species and compare how their olfactory systems detect these cues: what are the olfactory receptor genes involved, and how do these govern the response spectra of their olfactory receptor neurons?

 

Genetic Modifications of the Olfactory Sense

Olfactory receptor neurons and neurons in the central nervous system of living Drosophila can be manipulated through a variety of genetic techniques. Specific genes can be expressed in selected neurons to kill or silence them, or additional genes such as olfactory receptors can be expressed to change the properties of the neurons. By characterizing the effects on the olfactory system together with behavioural effects of these manipulations, we can deduce the function of specific neurons involved in olfactory behaviour. In addition, activity-dependent fluorescent dyes can be expressed in specific neurons to study their activity through optical imaging techniques.

 

Funding

The Linnaeus initiative "Insect Chemical Ecology, Ethology and Evolution" ICE3

 

Personnel

Mattias Larsson, Agnieszka Ruebenbauer, Lina Bryngelsson

 

Collaboration

Christer Löfstedt, (Lund University, Sweden)

 

Selected reference

Larsson MC, Domingos AI, Jones WD, Chiappe ME, Amrein H, Vosshall LB. 2004. Or83b encodes a broadly expressed odorant receptor essential for Drosophila olfaction. Neuron 43:703-714