Practice question

PAR family establishes early embryonic polarity without zygotic transcription relying solely on maternal proteins and sperm cue. PAR-2 RING finger protein recruited posteriorly after sperm centrosome signal suppresses anterior actomyosin contractility via RhoGAP regulation, preventing PAR-3/PAR-6/PKC-3 complex binding posteriorly. PAR-3 scaffolds anterior complex regulating cortical contractility and spindle positioning via GPR-1/2 and LIN-5. Mutual antagonism creates bistable cortical domains translated into cytoplasmic gradients MEX-5 anterior high and PIE-1 posterior high via differential phosphorylation. Conservation from worms to mammals underscores fundamental cortical polarity principle defining axes before gastrulation.