 In the 1980s Dr. Blau's findings challenged the prevalent view that the mammalian differentiated state is fixed and irreversible.In her famous heterokaryon experiments she fused differentiated cells of two different species to form stable non-dividing heterokaryons, and found that previously silent genes could be activated.As a result, human keratinocytes, hepatocytes and fibroblasts expressed muscle genes that they normally never would.