sentences:  In 1996 Nik Zeps published the first paper demonstrating label retaining cells were present in the mouse mammary gland and this was confirmed in 2005 by Gilbert Smith who also published evidence that a subset of mouse mammary epithelial cells could retain DNA label and release DNA label in a manner consistent with the immortal DNA strand mechanism.Soon after, scientists from the laboratory of Derek van der Kooy showed that mice have neural stem cells that are BrdU-retaining and continue to be mitotically active.Asymmetric segregation of DNA was shown using real-time imaging of cells in culture.