Practice question

Juxtacrine signaling requires cell-to-cell contact where membrane-bound ligand on one cell engages receptor on adjacent cell without secretion or diffusion. Notch-Delta interaction exemplifies this: Delta ligand presented on signaling cell binds Notch receptor on receiving cell, triggering ADAM and gamma-secretase cleavage and release of Notch intracellular domain that translocates to nucleus and activates Hes genes via Su(H) complex. BMP, Wnt and Sonic hedgehog are diffusible paracrine morphogens acting at distance via gradient. Contact-dependent Notch-Delta mediates lateral inhibition, boundary formation and binary fate choices during neurogenesis, somitogenesis and lymphocyte development ensuring precise patterning.