Practice question

Fertilization entry point defines posterior in C. elegans through centrosome-derived polarity cue. Sperm centrosome enters at one pole, initiating cytoplasmic streaming and actomyosin cortical flows that push PAR-3, PAR-6, PKC-3 and CDC-42 anteriorly, while PAR-1 kinase and PAR-2 RING protein accumulate posteriorly. Microtubule organizing center reorganizes cortex, establishing mutually exclusive domains via phosphorylation feedback. This sperm-position cue creates anterior-posterior axis before first mitosis, dictating unequal cleavage, spindle positioning, and segregation of P-granules and maternal mRNAs essential for asymmetric patterning and early developmental symmetry breaking.