Figure 2.
Various modes of regulation of niche signaling range. Niche-derived signaling molecules can be enriched in the vicinity of stem cells either by ligand-receptor interactions or by extracellular matrix components in order to generate a signal gradient across stem cells and their differentiating daughters for cell fate determination. Alternatively, niche signals can be precisely controlled by specialized subcellular structures including nanotubes and cytonemes in the stem cells (cytonemes are specialized filopodia. Although not drawn in the figure, cytonemes also concentrate ligands and receptors on their surface to allow very specific intercellular signaling events).
