If P2 is removed from the 4-cell stage embryo, what happens to EMS fate?
EMS fate specification integrates maternal SKN-1 and signal from neighboring P2 cell via MOM-2 Wnt pathway. P2 secretes MOM-2 and expresses MES-1, activating Src and Wnt cascades that lower nuclear POP-1 in posterior EMS daughter, allowing E fate. Anterior MS retains high POP-1. When P2 is ablated or removed at 4-cell stage, no Wnt signal reaches EMS, POP-1 remains high in both daughters, repressing endoderm program. Both progeny differentiate as MS-like cells producing mesoderm and pharynx, no intestine. This demonstrates inductive requirement for E patterning despite autonomous SKN-1 presence, showing P2-dependent polarization.
Ref: Goldstein 1993; Gilbert Developmental Biology Chapter 4: P2 removal effect - EMS produces two MS cells.