Practice question

Juxtacrine signaling requires direct physical contact between adjacent cells, where membrane-bound ligand presented on one cell surface binds receptor on immediate neighbor without diffusion. Canonical example is Notch-Delta pathway controlling lateral inhibition and binary fate decisions: Delta ligand activates Notch receptor triggering gamma-secretase cleavage and NICD transcriptional regulation that suppresses neural potential in receiving cell. Such contact-dependent communication ensures precise patterning at single-cell resolution without soluble intermediates, distinguishing it from paracrine diffusion over several cell diameters or endocrine circulation through bloodstream. Gap junctions also represent juxtacrine exchange of small metabolites.