EGFR signaling in the brain is necessary for olfactory learning in Drosophila larvae

Abstract

Signaling via the epidermal growth factor receptor (EGFR) pathway has emerged as one of the key mechanisms in the development of the central nervous system in Drosophila melanogaster. By contrast, little is known about the functions of EGFR signaling in the differentiated larval brain. Here, promoter-reporter lines of EGFR and its most prominent activating ligands, Spitz, Keren, and Vein, were used to identify the brain structures relevant for the EGFR pathway. Unexpectedly, promoter activity of all these pathway components was found in the mushroom bodies, which are known to be a higher brain center required for olfactory learning. We investigated the role of the EGFR pathway in this process by using different mutant larvae with reduced pan-neuronal EGFR signaling and those with reduced EGFR signaling in mushroom bodies only. Expression of a dominant-negative form of EGFR as well as silencing of the ligands via RNA interference was applied and resulted in significantly impaired olfactory learning performances. General defects in the ability to taste or smell as well as impaired EGFR signaling during embryonic development could be excluded as major reasons for this learning phenotype. In addition, targeted expression of a constitutively active form of the ligand Spitz also led to a significantly reduced learning ability. Thus, very low levels as well as very high levels of EGFR signaling are deleterious for olfactory learning and memory formation. We hypothesize that EGFR signaling in a certain range maintains a homeostatic situation in the mushroom bodies that is necessary for proper learning and memory.

The Role of Monoaminergic Neurotransmission for Metabolic Control in the Fruit Fly Drosophila Melanogaster

“…Other transgenic strains including nsyb-GAL4 (#51635), ppl-GAL4 (#58768), were obtained from the Bloomington Drosophila Stock Center. All flies, unless otherwise stated, were raised on standard yeast/cornmeal/agar medium at 25°C with about 50%–60% relative humidity under a 12 h/12 h light/dark cycle as described previously (Rahn et al, 2013 ; Li et al, 2015 ). RNAi-mediated knockdown of OAR/TARs genes in different tissues was achieved by crossing UAS-receptor RNAi line to the tissue-specific promoter GAL4 line and the F1 generation flies were kept at 29°C to enhance the RNA interference, the parental lines crossed to w 1118 were used as controls.…”

THE OCTOPAMINE RECEPTOR octß2R IS ESSENTIAL FOR OVULATION AND FERTILIZATION IN THE FRUIT FLY Drosophila melanogaster

“…The tissue was directly mounted on a slide with one drop of FocusClear (CelExplorer) medium. Each image was photographed and analyzed by using a Carl Zeiss HPX120 microscope (Zeiss, Göttingen, Germany) and Zeiss AxioVision 4.8 software (Rahn et al., ).…”

Expression analysis of octopamine and tyramine receptors in Drosophila

“…The analysis of peripheral expression sites was performed with native GFP fluorescence mostly using an Olympus SXZ12 steromicroscope equipped with epifluorescence (Olympus, Hamburg, Germany). Expression in the brain was analyzed following anti-GFP immunohistochemistry as described earlier (Rahn et al 2013). The brains were dissected in Drosophila Ringer's solution and immediately fixed in 4 % (w/v) paraformaldehyde in PBS for 1-2 h at room temperature.…”