Practice question

PAR-1 is serine-threonine kinase homologous to mammalian MARK2 microtubule affinity-regulating kinase, localizing to posterior cortex soon after fertilization following sperm-derived centrosome cue. Centrosome reduces anterior NMY-2 actomyosin contractility, allowing PAR-2 RING finger to recruit PAR-1 to posterior membrane via lipid binding. PAR-1 phosphorylates MEX-5, MEX-6 and PAR-3 at conserved serines to maintain anterior restriction, creating bistable cortical domains. Posterior enrichment ensures P-granule retention, proper spindle rotation via GPR-1/2, size asymmetry, germline segregation, and embryonic viability essential for polarity maintenance and lineage fidelity throughout early development.