Researchers map out networks that determine cell fate August 24,
2006 A two-step process appears to regulate cell fate decisions
for many types of developing cells, according to researchers
from the University of Chicago. This finding sheds light on a
puzzling behavior. For some differentiating stem cells, the
first step leads not to a final decision but to a new choice. In
response to the initial chemical signal, these cells take on the
genetic signatures of two different cell types. It often
requires a second signal for them to commit to a single cellular
identity. In the Aug. 25 2006 issue of Cell, the researchers,
working with hematopoietic stem cells, which give rise to the
many types of blood cells, show how "pioneer transcription
factors" trigger the first step, pushing these stem cells
towards this mixed lineage, midway between two related cell
types--in this case between a macrophage and a neutrophil. Then
one of two rival "secondary factors" activates the genes that
lead to one cell type and shuts d