Practice question

EMS blastomere, daughter of P1, generates MS mesoderm and E endoderm. Its polarity depends on POP-1, C. elegans TCF transcription factor downstream of Wnt/MAPK signaling from P2. In anterior daughter MS, high nuclear POP-1 represses endoderm genes; in posterior E maintained in contact with P2, Wnt signal phosphorylates POP-1 lowering nuclear levels and converting it to activator cooperating with SKN-1 and MED factors to induce END-1/3. Loss of POP-1 causes both daughters to become E-like, showing POP-1 essential for EMS asymmetry and proper endomesoderm specification throughout intestine and pharynx formation.