| dc.description.abstracteng | Cell turnover is an important biological process for maintaining tissue homeostasis. During cell turnover, newly generated cells replace unwanted cells to balance the number of cells and ensure the functionality of a tissue. Failure of cell turnover can lead to physiological complications. Therefore, it is of high interest to understand the mechanistic basis of cell turnover. Planarian flatworms, with their unique biology, can serve as a model to study cell turnover: Planarians undergo cell turnover on an organismal scale, continuously replacing all cells throughout their lifetime. In this process, adult pluripotent stem cells serve as the only source for generating new cells. Third, their flexible body size contributes to the dynamic maintenance of tissue homeostasis. Despite the interesting biology of planarian cell turnover, our knowledge of this process is limited due to the limited tools available.
To deepen our knowledge about this process, I developed two imaging assays to investigate cell turnover in planarians. In Chapter 2, I established a pulse-chase dye labeling assay to quantify the turnover rate of epidermal cells. The results show that the ventral epidermis is a very dynamic tissue with a half-life of 4.5 days. Interestingly, differences in turnover rates were observed between dorsal and ventral epidermis and between anterior and posterior epidermis. In Chapter 4, I developed a live imaging protocol to directly observe cell removal in the planarian epidermis. The results show that epidermal cells were eliminated by basal extrusion and entered the interior of the animal. In this process, basally extruded epidermal cells relocated to the intestine.
In summary, the imaging assays developed in this thesis allow for the quantification of the epidermal cell turnover rate and observation of the elimination of these cells. The findings show that cell turnover in the planarian epidermis involves basal extrusion and subsequent intestinal digestion, suggesting that extruded epidermal cells are recycled as an energy resource. | de |