Practice question

Lateral inhibition ensures tertiary fate protection. After induction, P6.p primary cell expresses LAG-2 ligands activating LIN-12 Notch in P5.p and P7.p, specifying secondary fate. Secondary cells also secrete DSL signals that activate LIN-12 in more distant P3.p, P4.p, P8.p. LIN-12 activation induces transcriptional repressors that prevent activation of LET-23 EGFR pathway by low LIN-3 and promotes hyp7 fusion via inhibition of egl-17 and vulval genes. Thus LIN-12 prevents LIN-3 activation from specifying vulval fate in tertiary cells, ensuring correct 3-2-1-2-3 pattern by restricting EGFR responsiveness through Notch-mediated lateral inhibition mechanism.