Protein Damage Control during Embryonic Stem Cell Differentiation: Role of the Proteasome

During the lifespan of organisms ranging from yeast to humans, there is an accumulation of macromolecular damage. However, these organisms produce youthful progeny with low damage levels. This thesis focuses on how this is accomplished. I have analyzed whether the levels of oxidatively damaged proteins change in mouse embryonic stem (ES) cells during the initial steps of cell specification (differentiation) from the pluripotent state. The results show that ES cells contain high levels of proteins modified by carbonyls and advanced glycation end products and that the identity of these damaged proteins, including chaperones and proteins of the cytoskeleton, are the same as those of aged tissues. However, early differentiation is accompanied by a dramatic drop in the damage of such proteins, both in cultured ES cells and in the blastocyst in vivo. //Text removed from public version// Moreover, the results support a model in which the restoration of low levels of protein damage at the start of each generation is achieved, in part, by a maintained capacity of the germ line to rid itself from such damage. //Text removed from public version/