Stem Cell Science
The size of organs in an adult organism typically remains constant despite the fact that many tissues continuously renew their structure. Stem Cell Science depends on the close control of a series of cellular events which includes the generation of new cells by division, the disposition of cells in space to generate tissue architecture, and the expression of a particular repertoire of genes for tissue function. It is changes in the normal steady state balance between these processes that underlie the in vivo generation of new tissue following damage or wounding.
The ability to manipulate such processes is clearly a necessary requirement for the in vitro generation of tissues by tissue engineering. It has recently become apparent that only a small fraction of proliferating cells, termed somatic stem cells, is capable of the continual self renewal and generation of differentiating cells required for maintain tissue function. A further finding of particular significance is that the commitment of adult stem cells to particular tissue lineages may be much more flexible than previously conceived and that they may share some of the properties of embryonic stem cells.
This raises interesting questions about how somatic stem cells can be amplified and their differentiation is controlled but also suggests that it may be possible to generate new tissues by reprogramming adult stem cells into new pathways of differentiation.