A new state of stem cell that could facilitate our understanding of early human development and evolution is described in Nature this week. The method used to produce the novel cell state enables human stem cells to differentiate when injected into a non-viable and non-intact post-implantation mouse embryo in a dish, which provides a platform for studying events that are otherwise difficult to approach, such as tissue specification.
Pluripotent stem cells (PSCs) have the ability to develop into any cell in the body. Two types of pluripotent cells have been isolated from embryos at different points during mammalian development: embryonic stem cells, which are able to differentiate into a broad range of cell types, and epiblast stem cells, which are primed for differentiation into specific cell types. These distinct states offer some insights into the processes that underlie pluripotency, but it has been suggested that they may not represent the full spectrum of pluripotent stem cells.
The alternative state identified by Juan Carlos Izpisua Belmonte and colleagues displays distinct characteristics, and the cells are named region-selective PSCs (rsPSCs) as they are shown to selectively colonize specific regions of isolated non-viable embryos. These rsPSCs can be efficiently obtained from cell lines in mice and primates (including humans), are easy to clone and can have their genomes edited with relative ease. Such cells could provide new tools for studying the role of pluripotency in mammalian development as well as having potential applications in regenerative medicine.