Abstract
The development of the nervous system is carefully coordinated to create a complex network of cells that allow an organism to perceive, interpret, and interact with their environment. One of the strategies employed to create this complex system is neuronal exuberance, where neurons are overproduced and then, if unneeded, are removed via programmed cell death. To clear the resulting widespread cell death, cells called phagocytes clean up the debris. Most of this is done by microglia, the professional phagocyte of the nervous system. However, it is not well understood if and how other cells, acting as ‘non-professional’ phagocytes, contribute to cell clearance during normal development. In this dissertation, we explore how one such cell type, the radial astroglia, behaves during early zebrafish development. In particular, we look at these cells during a wave of neuronal cell death in the optic tectum. We show that radial astroglia form large spherical structures from their thin basal processes that are highly dynamic and often long-lasting. After thorough investigation, we concluded that these structures have not previously been described and named them “scyllate heads.” We developed tools and techniques to study scyllate head behaviors. Throughout this dissertation, we demonstrate that scyllate heads surround the majority of dying neurons, but do not usually become phagocytic. Instead, we show that scyllate heads usually dissipate by passing their contents to microglia, which complete the phagocytic process. We explore these and other behaviors under both homeostatic and manipulated conditions. This research reveals a new role for radial astroglia in early development and raises many questions about the participation of non-professional phagocytes in cell clearance more broadly.
