Drosophila Melanogaster As a Model Organism
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How individual olfactory receptors affect olfactory guided behavior in Drosophila Dissertation To Fulfill the Requirements for the Degree of „doctor rerum naturalium“ (Dr. rer. nat.) Submitted to the Council of the Faculty of Biology and Pharmacy of the Friedrich Schiller University Jena by Dipl. Biol. Tom Retzke born on July 14th, 1988 in Wolfen, Germany Reviewers 1. 2. 3. Date of public defense _______________________ 2 | Page “Stay awhile and listen!” (Deckard Cain) 3 | Page Table of Contents Table of Contents Introduction .................................................................................................................................... 5 Drosophila melanogaster as a model organism .......................................................................... 5 The olfactory system of Drosophila melanogaster ..................................................................... 7 Intraspecific connections: It´s all about communication .......................................................... 11 Interspecific connections: If the relationship is one-sided ....................................................... 13 Aims of this thesis ........................................................................................................................ 16 Manuscript Overview ................................................................................................................... 18 Manuscript I .................................................................................................................................. 23 Manuscript II................................................................................................................................. 32 Manuscript III ............................................................................................................................... 42 Manuscript IV ............................................................................................................................... 53 Manuscript V .............................................................................................................................. 119 General Discussion ..................................................................................................................... 139 Trust is good, control is better – importance of proper controls ........................................... 139 A new way flies communicate and how this is modified by others ........................................ 143 Behavioral responses to binary mixtures and their processing .............................................. 148 Different food preferences in larval and adult flies ................................................................ 155 Perspective and future questions ........................................................................................... 157 Summary ..................................................................................................................................... 160 Zusammenfassung ...................................................................................................................... 163 References .................................................................................................................................. 167 Declaration of Independent Assignment .................................................................................. 192 Curriculum Vitae ......................................................................................................................... 193 Acknowledgements .................................................................................................................... 194 4 | Page Introduction Introduction Up to date there is no general definition for what is life. But most of the definitions share some ideas. According to the Oxford Dictionary life “includes the capacity of growth, reproduction, functional activity and continual change preceding death”. Koshland (2002) postulated seven pillars (program, improvisation, compartmentalization, energy, regeneration, adaptability, seclusion), which build the fundament of the temple of life. The common ground of those descriptions of life is the ability to move and to react to environmental changes. To fulfill the latter, living organisms are equipped with abilities to detect heat, sonic waves, light, wind, magnetic fields, etc. – commonly known as senses. One of the oldest among them is chemosensation. Although even unicellular organisms are able to detect changing concentrations of chemicals in water (Bondoc et al., 2016), higher animals, have developed two distinct chemical senses: gustation for the detection of close-range chemical cues, and olfaction for the detection of volatiles over sometimes amazingly long distances. One of the most famous model organisms to study olfaction is the fruit fly Drosophila melanogaster. Drosophila melanogaster as a model organism The first description of the vinegar fly Drosophila melanogaster was made 1830 by Johann Wilhelm Meigen, a German entomologist. 75 years later, in 1905, the first scientific paper dealing with Drosophila as a laboratory animal was published by Frederick W. Carpenter (Carpenter, 1905). Thomas Hunt Morgan, an American 5 | Page Introduction geneticist, finally established the vinegar fly in the beginning of the 20th century in his laboratory (Davenport, 1941). Hence he paved the way to the success of this fly as one of the main biological models by investigating and revealing the general chromosomal structure and its meaning in heredity (Nobel Prize 1933). Furthermore the popularity of Drosophila as a model organism increased because of its short generation time of 8 to 13 days (Mavor, 1927), depending on temperature, and its simplicity to breed. Over decades and across disciplines this model organism supported several Nobel-Prize-awarded discoveries (Hermann Müller in 1946; Edward B. Lewis, Christiane Nüsslein- Volhard and Eric F. Wieschaus in 1995; Richard Axel and Linda Buck in 2004; Jules Hoffman, Bruce Beutler and Ralph Steinmann in 2011). Investigations of the circadian rhythm (Konopka and Benzer, 1971) and the learning behavior (Dudai et al., 1976) of Drosophila form the fundament for the analysis of genetic basics in fly behavior. Since this time a huge amount of genetic tools were developed, allowing cell-specific manipulation, including the artificial activation or silencing and visualization of certain cell types or whole cell populations (Venken et al., 2011). Especially the olfactory system of the vinegar fly was spotlighted during the last decades using these approaches (de Bruyne et al., 2001; Couto et al., 2005; Vosshall and Stocker, 2007; Stensmyr et al., 2012; Grabe et al., 2014; Dweck et al, 2015). 6 | Page Introduction The olfactory system of Drosophila melanogaster Drosophila uses odors to detect, localize, and judge food (Stensmyr et al., 2012), oviposition sites (Dweck et al., 2013) and mating partners (Ziegler et al., 2013). Odors are emitted by different sources in a fly´s environment and are basically blends of many different molecules. To detect these molecules flies are equipped with two specialized paired head appendices, the antennae and the maxillary palps. Both olfactory organs are covered with hair like structures, so-called sensilla (Couto et al., 2005; Benton et al., 2009). While the antennae carry around 500 sensilla each, only 50 can be found on the maxillary palps (Grabe et al., 2016). At the end of the 20th century de Bruyne et al. (1999) showed that these sensilla have numerous pores on their surface. Odor molecules can travel through these pores and reach the sensillum lymph, where they are picked up by odor binding proteins (OBPs). OBPs serve as a kind of ferry to transport the – usually hydrophobic – odor molecules through the hydrous sensillum lymph to chemical receptors (Fan et al., 2011). Up to date we know three different classes of chemical receptors in Drosophila: olfactory receptors (ORs; Clyne et al., 1999; Gao and Chess, 1999; Vosshall et al., 1999), ionotropic glutamate receptors (IRs; Benton et al., 2009) and gustatory receptors (GRs; Clyne et al., 2000; Smith, 2001; Jones et al., 2007 ). At least for ORs and IRs specific co-receptors have been identified, which form a functional dimer with the chemoreceptors. 2004 Larsson et al. found that OR83b is ubiquitously expressed and they called it orco (olfactory receptor co-receptor) and Wicher et al. (2008) found evidence, that orco is necessary for signal transduction. While on the antennae we find ORs and IRs and two GRs detecting CO2 (GR21a/GR63a; Jones et al., 2007; Kwon et al., 2007), the 7 | Page Introduction maxillary palps carry ORs and IRs only and the remaining GRs are located on the flies´ labellum, legs, wings and the ovipositor (Stocker, 1994; Vosshall and Stocker, 2007; Liman et al., 2014). On the antenna each sensillum hosts the OR or IR exposing dendrites of 1 – 4 olfactory sensory neurons (OSNs), which express – with a few exceptions – only one type of OR or IR (Fig. 1A; Couto et al., 2005). When odor molecules bind to the ligand-specific receptors the neuron becomes activated, indicated by an action potential. The generated signal spreads from the dendrites over the soma to the axon of an OSN. All OSN axons of one antenna are bunched and draft from the periphery to the protocerebrum, more precise to the antennal lobe (AL). The AL consists of spherical subunits, so-called glomeruli, and each glomerulus is innervated by all