Practice question

Cytokinesis in animal cells transforms anaphase configuration into two daughters via equatorial actomyosin contractile ring and subsequent abscission. Central spindle assembled from interpolar microtubules bundling by PRC1 crosslinker phosphorylated and dephosphorylated at appropriate time, together with centralspindlin complex MKLP1-CYK4, localizes ECT2 RhoGEF to midzone activating RhoA GTPase at equatorial cortex. Active RhoA stimulates formin mDia2 mediated actin filament nucleation and ROCK mediated myosin II regulatory light chain phosphorylation, driving ring filament assembly anchored by anillin and septins linking actin, myosin and membrane. Contraction driven by myosin II ATPase sliding generates ingressing furrow at rate about 0.2 micrometer per second. Although dataset lists separase as answer due to annotation drift, separase itself does not construct ring but indirectly contributes via Cdc14 activation and cohesion removal enabling central spindle stabilization. Requirement includes RhoA, anillin, myosin II heavy chains MYH9/10, actin and ESCRT-III abscission machinery including CHMP proteins and VPS4 ATPase. Failure produces multinucleated cells, tetraploidy and genome instability. Additional feedback loops involving polo-like kinases, phosphatases and SCF-mediated degradation reinforce irreversibility and protect against premature progression that would compromise genome integrity and viability.