In order to determine whether ERCs play a role in age-associated LOH, it is necessary to eliminate ERC formation and/or accumulation in aging cells. Using the bud6Δ strain we reduced ERC levels at a median RLS by approximately 50%, down to a level that was equivalent to a younger wild type population (26 hours of replicative aging; Figure 8B). It is significant that at this younger age, wild type cells show no increase in LOH rate at the MET15 locus. Despite this reduction in ERC levels, the bud6Δ strain showed no suppression of age-associated LOH with age. While we interpret this as evidence that ERC accumulation does not drive age-associated LOH at MET15, it remains formally possible that this reduced level of ERCs is still above a threshold required to increase LOH, or that a subpopulation of cells contain higher ERC levels that drive age-associated LOH events. A clearer understanding of the contribution of ERCs to age-associated LOH will require more refined control of ERC initiation and accumulation.
