Molecules that reverse cellular aging and rejuvenate human cells without altering the genome. Sinclair and his team developed high-throughput cell-based assays that distinguish young from old and senescent cells, including transcription-based aging clocks and a real-time nucleocytoplasmic compartmentalization (NCC) assay. In 2006, Takahashi and Yamanaka demonstrated that the expression of four transcription factors, OCT4, SOX2, KLF4, and c-MYC (collectively known as "OSKM"), reprograms the developmental potential of adult cells, enabling them to be converted into various cell types. These findings initiated the field of cell reprogramming, with a string of publications in the 2000s showing that the identity of many different types of adult cells from different species could be erased to become induced pluripotent stem cells, commonly known as "iPSCs".