Practice question

MOM-2 encodes C. elegans Wnt homolog expressed in P2 blastomere at 4-cell stage. It binds MOM-5 Frizzled receptor on EMS, collaborating with MES-1/SRC-1 pathway to activate WRM-1 beta-catenin and MAPK signaling, resulting in phosphorylation and downregulation of POP-1 TCF in posterior daughter E. Converted POP-1 together with higher SYS-1 beta-catenin activates transcription of end-1, end-3 endoderm determinants. mom-2 mutants phenocopy loss of P2 signal, causing both EMS daughters to become MS-like. Thus primary function of MOM-2 is to activate Wnt signaling establishing EMS polarity and endoderm specification.