Defining the programmed proteome rejuvenation underlying gametogenesis

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ABSTRACT The integrity of a cell depends on the quality of its components. These components include proteins, which are responsible for executing most cellular functions, many through organization into stable complexes. A hallmark of aged cells is the breakdown of protein integrity, or proteostasis, which results from the damage to key proteins and complexes over time, leading to more accumulated damage, and ultimately cell dysfunction. The specific proteome components that are most susceptible to damage and that drive its accumulation remain unclear, but the survival of future generations depends on protection of one cell type—gametes—from inheriting damaged components from their precursor cell. During gametogenesis in the simple budding yeast, as a precursor cell is differentiated into gametes, we observe the degradation of many cellular structures and proteins, followed by their resynthesis and reorganization. This cellular restructuring is associated with an active rejuvenation program that allows equivalently young gametes to be produced from old or young precursor cells. The mechanisms that contribute to this natural rejuvenation program are not known, but it can be recapitulated by exogenous expression of a meiotic transcription factor in aged mitotic cells, suggesting that it is portable. Gametogenesis in yeast thus offers the opportunity to watch as the cell shows us what proteins and complexes it needs to reset and reorganize to ensure cellular youth, and the mechanisms it uses to achieve this. Of particular interest are proteins of basal or “housekeeping” function, including the ribosome, which are long- lived in mitotic cells, but degraded and replaced at great energetic cost during gametogenesis. We also observe reorganization of abundant housekeeping complexes, including the proteasome, during gametogenesis, and aggregation of some proteins, including superoxide dismutase 1 (Sod1), at the time of their degradation. Together, these observations suggest that yeast cells remodel their proteome during gametogenesis as a quality control measure. Here, we propose to identify the key set of cellular components, with a focus on “housekeeping” proteins, that are reset as gametes are created from precursor cells. We use a proteomic approach to globally define changes to protein complexes during gamete construction, and specifically determine proteasome remodeling and activity over time. We investigate the links between aggregation of proteins, including Sod1, and protein oxidation and degradation. Finally, we identify the specific degradation mechanisms that drive key aspects of proteome remodeling and test their necessity for gamete rejuvenation and ability to drive lifespan extension when exogenously activated. This project will build an atlas to reveal the proteins and complexes that are important enough for young cell identity to warrant the energetic cost of resetting them during gamete formation, as well as those that may be toxic enough to warrant their active removal. By identifying and manipulating the specific pathways used by gametes to selectively remodel their proteome, we will find strategies that can be co-opted to combat and prevent age-associated cellular damage.