Centriolar cycle of fused cells.

Ultrastructure of centrioles of fused cells containing heterophasic interphase nuclei, premature chromosome condensation, and a telophase-like nucleus were studied. The study indicated that the heterophasic cellular environments contributed by the different cell partners exert a mutually opposite effect on the structure of centrioles. The G1-cell partner suppresses replication of S-centrioles. Asynchronous replications of G1 and S-stage centrioles were observed in some G1-S, G1-G2 and S-G2 fused cells. In interphase-mitotic fused cells, centrioles of interphase stages underwent mitotic activation when their nuclei were induced to premature chromosome condensation. Daughter centrioles of G1-, S-, and G2-stages were also capable of mitotic activation independently if they were separated from their mother centriole. Inactive centrioles were observed in some cells containing G1-premature chromosome condensation. When mitotic nuclei were induced to telophase-like nucleus formation, their centrioles were also inactivated. Concomitant events of induced nuclear and centriolar changes suggest that they might have been controlled by the heterophasic cytoplasmic factors through similar pathways.