by Joe Delaney, 1st year MCB PhD student
Our collaborator, Brian Kennedy, is in the finishing steps of a genome-wide replicative lifespan study designed to find out which single gene deletion mutants are able to divide significantly more times than wild type cells. These 80-100 genes form the basis of a network which regulates replicative aging in yeast. While previous reports have already shown a number of pathways from this screen to be important (GCN4 activation by Steffen KK et al Cell 2008, and TOR1/SCH9 regulation by Kaeberlein et al Science 2005), most of the genes do not have an immediately recognizable reason for their age extension.
One of my current projects is to define a subset of these genes which are involved in a yeast-specific form of aging: the accumulation of extrachromosomal ribosomal DNA circles (ERCs). These ERCs were previously found to be important through studying the effects of FOB1 deletions and SIR2 overexpression; FOB1 deletion reduces recombination around the rDNA loci and hence reduces ERC formation. SIR2 overexpression yields a similar phenotype, so these genes act antagonistically at the rDNA loci to promote or inhibit ERC formation. Since previous studies in the lab have shown that SIR2 has ERC-independent functions that extend lifespan, one of the ways to find these is to find which genes are both in the SIR2 pathway and which do not act like FOB1 to reduce ERC formation. The strategy which I am undertaking to explore which subset of long lived genes are acting in the FOB1 pathway is by creating SIR2 deletions in all the long lived strains and seeing if the lifespan is extended as it would be with a FOB1 deletion. Ultimately, this will help us parse out different functions for subsets of our long lived deletion collection and help us understand which pathways these genes are active in.