Practice question

Upon C. elegans fertilization, oocyte and sperm pronuclei must migrate to meet. After sperm entry at posterior, sperm aster nucleates microtubules. Female pronucleus migration toward centrosome depends on minus-end directed motor dynein anchored on nuclear envelope via SUN-1, ZYG-12 LINC complex. Dynein pulls microtubules, drawing pronuclei together for fusion before first mitosis. Kinesin drives opposite plus-end movement, myosin actin provides cortical but not directed migration. Mutation in dhc-1 heavy chain or dnc mutants blocks pronuclear meeting, resulting in failed karyogamy and embryonic arrest, demonstrating dynein essential for pronuclear migration during fertilization.