Which pathway is required for distinguishing ABa and ABp cells?
Early C. elegans embryo distinguishes AB daughters ABa and ABp via Notch signaling integrating cell contact geometry and timing. At four-cell stage, P2 expresses APX-1 Delta ligand contacting ABp but not ABa due to spatial arrangement and spindle orientation governed by PAR polarity. APX-1 binds GLP-1 Notch receptor on ABp, gamma-secretase cleavage releases intracellular domain that activates lag-1 transcription factor and bHLH repressors ref-1 family. This induces distinct transcriptomes; ABa generates anterior pharynx and neurons while ABp generates dorsal posterior structures. Without GLP-1
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 8: Notch signaling distinguishes ABa and ABp via GLP-1 and APX-1.
