Analyzing receptor responses in the Drosophila Johnston's organ with two-photon microscopy
von Philipp Jähde
Datum der mündl. Prüfung:2016-08-24
Erschienen:2017-07-31
Betreuer:Prof. Dr. Martin Göpfert
Gutachter:Prof. Dr. Martin Göpfert
Gutachter:Prof. Dr. André Fiala
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http://dx.doi.org/10.53846/goediss-6371
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Name:phd_thesis_philipp_jaehde.pdf
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Zusammenfassung
Englisch
Hearing organs rely on force-gated ion channels to convert the mechanical energy imposed by sound into receptor potentials usable by the nervous system. So far, little is known about the identity and working mechanisms of these channels, but in recent years several candidate proteins have emerged which seem to be key elements of force transduction systems. In the fruit fly Drosophila melanogaster, two proteins involved in the function of several mechanosensory organs are the transient receptor potential channel subunits Inactive and NompC (No mechanoreceptor potential C). Mutations of both proteins strongly impair the function of many mechanosensory organs, an influence which has been best studied in the Johnston's organ (JO), the mechanosensitive neurons of the Drosophila ear. Recent studies came to different conclusions about the specific roles of Inactive and NompC, but all of them agree in the observations that loss of Inactive changes the active amplification properties of the JO, and disrupts the transmission of auditory signals into the brain. Mutations of NompC instead prevent active amplification of faint sounds, but the JO retains a certain amount of sound sensitivity. All of these studies used experimental methods lacking spatial resolution, and thus had to base their conclusions on the response of large groups of JO neurons. In this thesis I adopted an existing widefield calcium imaging method for two-photon excitation microscopy, increasing the spatial resolution to single scolopidia (assemblies of two to three sensory neurons). This method thus allowed me to study the influence of nompC- and inactive mutations on individual receptor units of the JO. Measuring individual responses of the JO neurons of control flies revealed a much higher diversity of response characteristics as distinguishable before. While the separation into highly sound-sensitive and less sensitive wind-detecting neurons found in earlier studies could in general be confirmed, especially the more sensitive cells showed a much larger response variability than detectable with group recording methods. Analysis of sound responses in mutant backgrounds revealed that both mutations do not remove the mechanosensitivity of all sensory neurons: Whereas inactive leaves small residual responses in some sensory neurons, nompC leads to several different response changes. Differing from earlier studies, some of the sound-sensitive cells remain mechanosensitive (even though with decreased sensitivity) and only in a few sound responses are abolished. In addition, several JO neurons react to sound stimulation with a negative calcium signal, which is a so far unobserved effect of the nompC mutation. Concluding from my results, neither Inactive nor NompC are “the” transduction channel of all Drosophila auditory neurons. Which roles they play in mutant neurons with remnant mechanosensitivity remains to be investigated.
Keywords: Drosophila melanogaster; Hearing; Mechanotransduction; Johnston's organ; NompC; Inactive; Two-photon microscopy; Calcium imaging; Mechanosensation; Transient receptor potential channel; TRP
