Page "Stem cell" Paragraph 24

Nearly all research to date has made use of mouse embryonic stem cells ( mES ) or human embryonic stem cells ( hES ).

Both have the essential stem cell characteristics, yet they require very different environments in order to maintain an undifferentiated state.

Mouse ES cells are grown on a layer of gelatin as an extracellular matrix ( for support ) and require the presence of leukemia inhibitory factor ( LIF ).

Human ES cells are grown on a feeder layer of mouse embryonic fibroblasts ( MEFs ) and require the presence of basic fibroblast growth factor ( bFGF or FGF-2 ).

Without optimal culture conditions or genetic manipulation, embryonic stem cells will rapidly differentiate.