Wnt signaling and the regulation of stem cell function

Canonical Writ signaling plays a crucial role in controlling cell expansion in many types of stem cells. Recent studies, however, demonstrated that Writ is not only a general stem cell growth factor but can also influence cell lineage decisions in certain stem cell types by promoting specific fates at the expense of others. Thus, Writ signaling elicits multiple functions in stem cells. Writ activity appears to depend on cell-intrinsic properties that might change with time during development, thereby altering the cellular response to Wnt. Moreover, the spatial context of a stem cell also determines how the cell interprets Writ signal activity, in that synergistic or antagonistic signaling pathways can modulate Writ signaling. How a stem cell integrates Writ and other signals and how such signaling networks regulate stem cell function on the molecular level remains to be elucidated.