Özet:
Neurogenesis in the adult nervous system is a limited process in higher vertebrates. The olfactory epithelium (OE) is an exception to this limitation and maintains the ability to regenerate lost neurons throughout the lifetime of the organism. Chemosensory neurons have a limited lifespan and need to be replaced continuously by new neurons. The zebrafish OE contains at least four morphologically distinct types of chemosensory cells that are molecularly characterized by their expression of different chemoreceptors. Even though a basic understanding of molecular events involved olfactory neurogenesis has emerged, little is known about the cell type specificity of this process. To address the question whether stem cell / progenitor activity in the OE is cell type-specific, an experimental paradigm to selectively ablate distinct subpopulations of chemosensory neurons in vivo was devised. To this end, transient transgenic zebrafish embryos expressing the bacterial nitroreductase (NTR) gene under the control of the cell type-specific OMP promoter were generated. NTR converts the prodrug metronidazole (MTZ) into a cytotoxic product that selectively kills the cells that express the NTR enzyme. The studies presented in this thesis aim to understand, if a selective loss of OMP expressing ciliated cells can be achieved and if this loss results in increased neurogenesis to selective replace the lost cell type. Results of MTZ treatment in early NTR-expressing embryos suggest that MTZ treatment efficiently and specifically kills transgenic neurons. However, the rate of ongoing neurogenesis during early embryonic development masks the effect of cell ablation, especially at later experimental time points. Transgenic constructs expressing the photo-convertible fluorescent protein dendra2 along with NTR should enable the distinction between previously existing cells and cells that were born after the onset of metronidazole treatment. Yet, the limited stability of converted dendra2 in sensory neurons limits this analysis to short experimental time windows.
