Lateral inhibition in C. elegans vulval differentiation

(a) Inhibitory signal Cell closest to anchor cell differentiates with 1° fate and then inhibits neighboring cells from 1° fate. Center cell (P6.p) detects more UN-3 signal (green), up- regulates lateral signal (blue) and down-regulates receptor (yellow). Left and right cells (P5.p and P7.p) receive more signal (blue) from center cell and up-regulate receptor (yellow) while down-regulating lateral signal (blue). Strong activation of Iin-3/Iet—23 pathway promotes 1° cell fate, in turn activating the Iag-Z/Iin-lZ pathway, which promotes a 2° cell fate in neighboring cells.