This manuscript investigated how growth of beta-cells are controlled in adult pancreas. Beta-cells located in the pancreas produces insulin and is critical for the maintaining blood levels of glucose in healthy individuals. Using mouse models that we engineered to lack a protein (PTEN) that controls the growth potential of the cells, we have found that we can increases the total number of beta cells and make the mice better at handling high glucose levels. In this manuscript, we further found that this effect of PTEN is particularly obvious in the old beta-cells. This finding is very important to Diabetes which often develop in middle-aged and older populations. We also discovered that PTEN controls the levels of a protein that is responsible for the lack of growth in aged beta-cells.