What duration of knockdown can I expect with shRNA?
Theoretically, production of the shRNA and knockdown should be a permanent condition. We see stable and permanent knockdown in cells that were transduced and cultured for over 1 year. These cultures were grown from a single resistance cell (clonal selection). We have seen populations of cells that have not undergone clonal selection shift over time, which is sometimes interpreted as a change in knockdown. What is actually happening is that within the heterogenous population of cells, there are varying effects from the knockdown. As you can imagine, some cells may outpace others in their growth, and as a result the percentage of knockdown seen varies over time as the population of the cell culture shifts.
