Practice question

PAR proteins, partitioning defective family identified in C. elegans zygote, establish anterior-posterior polarity essential for asymmetric divisions of P lineage. PAR-3, PAR-6, PKC-3 localize anteriorly, PAR-1, PAR-2 posteriorly after fertilization, driven by sperm centrosome cues and actomyosin flows. This restricts P-granules, PIE-1, SKN-1, MEX-5/6 to posterior blastomere P1, ensuring germline versus somatic divergence. Mutations in par genes randomize AB versus P1 divisions, causing symmetric divisions and loss of endoderm. They do not directly regulate vulval signaling, functioning primarily in early polarity establishment of embryo axis.