Cell-biological aspects of the prion protein in transgenic Xenopus intermediate pituitary cells

Abstract

In mammals, prions are the causative agents of various neurodegenerative diseases (e.g. scrapie, mad cow and Creutzfeldt-Jakob disease) in which the three-dimensional structure of the normal cellular form of the prion protein (PrPC) is misfolded into the infectious scrapie form (PrPSc or prion). In the brain, PrPSc molecules tend to aggregate and spread rapidly from cell to cell. Despite its clear role in neurodegenerative diseases, the normal physiological function of PrPC remains elusive. The goal of the research described in this thesis was to exploit the melanotrope cells of the intermediate pituitary of the South-African claw-toed frog Xenopus laevis as a model system to study cell-biological aspects of Xenopus PrPC functioning in vivo. Chapter 1 provides a general introduction to the various topics dealt with in this thesis. The research described in the first experimental chapter focuses on the temporal and spatial mRNA expression patterns of PrP in Xenopus (chapter 2). In chapter 3, the technique of stable Xenopus transgenesis in combination with a POMC gene promoter fragment was used as a tool to express Xenopus PrPC fused to the green fluorescent protein GFP specifically in the Xenopus melanotrope cells, and to study the biosynthesis and intracellular fate of GFP-PrPC in this highly specialized neuroendocrine cell. Chapter 4 reports the functional analysis of Xenopus melanotrope cells transgenic for the GFP-PrPC protein. Chapter 5 describes a biosynthetic and functional analysis of transgenic Xenopus melanotrope cells expressing mutated forms of the GFP-PrPC fusion protein (the non-cleavable GFP-PrPCK81A, the GPI-deleted GFP-PrPC?GPI, the octarepeat-containing GFP-PrPCocta and the GFP-GPI mutant proteins). Finally, in chapter 6 we discuss the results described in this thesis and put them in a broader perspective. We propose a model regarding the effect of overexpressed PrPC on the transgenic Xenopus intermediate pituitary cells