Proteinaceous infectious particles or prions are self-perpetuating alternate conformations of proteins that are the causative agents of pathologies in mammals (including Humans) and of heritable non-mendelian traits in filamentous fungi and yeast. We have showed that the cytotoxic fibrillar aggregates which are believed to be at the origin of several neurodegenerative diseases (Alzheimer, Parkinson, Huntington) behave as prions that propagate their abnormal conformation from neuron-to-neuron. The yeast Saccharomyces cerevisiae hosts many prion or prion-like proteins, unrelated in sequence and function, which proved to be excellent models for understanding the mechanisms of epigenetic structural inheritance.

Specifically, we are interested in the mechanisms of propagation, elimination and degradation of the yeast prions Sup35p and Ure2p. We have highlighted a role for the proteasome, a major cellular proteolytic nanomachine, in the degradation of both the native and aggregated forms of these prions. More recently, we reported that these prions are secreted within extracellular vesicles in their aggregated and infectious conformation. Among the possible implications of our work is the possibility of previously unsuspected extracellular vesicle-mediated horizontal cell-to-cell transfer of fungal prions. We now aim at pursuing this work by documenting the role of the vesicular traffic and autophagy in the secretion, degradation and the vertical or horizontal transfer of yeast prions.

The thesis project will specifically aim at answering the numerous questions raised by our findings: are yeast prions targeted for degradation by autophagy and under which conditions? How and when are the aggregated forms of these prion proteins packaged within extracellular vesicles? What are the structural determinants, the cellular factors and the signals that regulate these processes? Are extracellular vesicles more than just cellular trash bins or do they play more elaborate roles as vectors of the horizontal transfer of genetic information in general and of yeast prions in particular?

This is a highly multidisciplinary project that will combine in vitro approaches using purified components (prions, extracellular vesicles) with cell biological, cellular biochemistry and molecular genetics approaches.