Reciprocal Induction and Lateral Inhibition
■ Ephrins are cell-surface signaling ligands whose receptors (Ephs) are receptor tyrosine kinases.
■ B-class ephrins and their receptors (EphB), each acting as both a ligand and a receptor, can mediate reciprocal induction in adjacent cells (see Figure 15-35).
■ Interactions between the Notch receptor and its transmembrane ligand Delta are used in lateral inhibition, which can control the choice between two alternative cell fates.
■ An initial random or biased fluctuation in signaling between two adjacent equivalent cells can trigger a regulatory circuit that amplifies the initial difference, leading eventually to one cell expressing only Delta ligand and the other expressing only Notch receptor (see Figure 15-36).
■ In C. elegans, Notch-mediated lateral inhibition causes two initially equal cells to follow different developmental paths.
■ In Drosophila, newly formed neural precursor cells (neu-roblasts and sensory organ precursors) express high levels of Delta and use Notch signaling to prevent their neighbors from becoming neural precursors (see Figure 15-38). Similar Notch-mediated lateral inhibition controls the balance between neural and non-neural cells in the development of Xenopus laevis.
Integrating and Controlling
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