New type of stem cell discovered

The naïve-like stem cell – a type so elusive it was thought not to exist – has been found by scientists from Bath and Berlin in what they have termed a Eureka moment. The new type of stem cell can develop into any type of cell and has huge potential for regenerating damaged tissue or reducing the need for organ transplant. Human embryonic stem cells (ESCs) are capable of transforming into several different types of cell but their fate is pre-determined. These new naïve-like cells – previously only found in mice – can differentiate into any cell type. “Most stem cells are primed to some extent to become a certain type of cell. If you use the analogy of a train network, these cells are like one of the main London stations. Trains from Paddington can go to Cardiff or Exeter, but not to Norwich. In the same way, these cells can develop into a fixed number of different cell types,” said Professor Laurence Hurst from the University of Bath. “However the naïve-like cells we’ve identified are like a central terminus; they are present earlier in the embryo’s development and so we think their fates can go in any direction and become any type of cell.” The naïve-like stem cells were found by studying which genes were expressed in very early embryos. HERVH – human endogenous retrovirus H has become integrated into human DNA and was very highly expressed at the right time and place in human embryos where scientists would expect to see naïve-like stem cells if they existed. The protein LBP9 is essential for HERVH activity in early embryos, and using a reporter system in which cells expressing the gene via LBP9 glowed green, the scientists found they had purified cells showing all the hallmarks of a mouse naïve cell. “Our human naïve-like cells look remarkably like the mouse ones, and express the same sorts of genes as the human inner cell mass (ICM) in the embryo, just as expected of naïve cells,” said Yichang Wang from MDC and first author of the paper in Nature. These cells also have features unique to humans and the team hope to investigate this further. “We were very excited by this discovery,” said Dr Zsusanna Izsvák from the Max Delbrück Centre for Molecular Medicine (MDC) in Berlin. “It was one of those Eureka moments that rarely happens in science.” Primate-specific endogenous retrovirus-driven transcription defines naive-like stem cells