Pluripotent stem cells are capable of developing into cells of the three embryonic germ cell layers (ectoderm, endoderm, mesoderm) as well as into the germ line of an organism. They can finally differentiate into any cell type of an organism, as they are still not determined to become a particular tissue type. Human embryonic stem cells differ from the embryonic stem cells of mice in that the so-called naive mouse stem cells resemble the inner cell mass from which the embryo develops. This is generally not the case in the human embryonic cell lines which researchers usually work on in the laboratory.

According to a press release, the researchers Jichang Wang, Gangcai Xie and Dr. Zsuzsanna Izsvák from the Max Delbrück Center (MDC), Berlin, and Prof. Laurence D. Hurst from the University of Bath in England detected human endogenous retroviruses H (HERVH) that integrated themselves into the human genome millions of years ago, losing their viral properties in the process. They are nonetheless still active at a very early stage of human embryo development, switching on HERVH gene sequences via a transcription factor called LBP9, which in turn activate a number of genes in the human embryonic stem cells, bringing the cells to the pluripotency stage.

The scientists used a fluorescent reporter mechanism to make the cells that switch on HERVH via the factor LBP9 luminesce green in a petri dish, thus identifying the human stem cells that switch on the HERVH virus and subsequently carry all the important features of a naive human stem cell. When they turned down LBP9 or the HERVH virus, the cells no longer looked like original human embryonic stem cells, but rather like the cell lines commonly used until now in laboratories.

These findings are of great importance for stem cell research. The scientists assume that in nature HERV is turned on only briefly in the cells because otherwise could never develop an embryo and differentiated cells.

The mechanism of pluripotency is not phylogenetically conserved and does not occur naturally in mice this way, which is why one reason for the difference between human and mouse stem cells.

Literature:
Jichang Wang & Xie & Gangcai, Manvendra Singh, Avazeh Ghanbarian T., Tamás Rasko, Attila Szvetnik, Huiqiang Cai, Daniel Besser, Alessandro Prigione, Nina V. Fuchs, Gerald G. Schumann, Wei Chen, Matthew C. Lorincz, Zoltán Ivics Laurence D. Hurst & Zsuzsanna Izsvák (2014): Primate-specific endogenous retrovirus-driven transcription defines naive-like stem cells. Nature. doi: 10.1038 / nature13804

Source:
http://www.innovations-report.de/html/berichte/biowissenschaften-chemie/forscher-in-berlin-und-bath-identifizieren-nahezu-urspruengliche-menschliche-stammzellen.html