Enforced cytokinesis without complete nuclear division in embryonic cells depleting the activity of DNA topoisomerase IIα

Abstract

Background: There are two distinct DNA topoisomerase II (topo II) isoforms, designated topo IIα and topo IIβ, in mammalian cells. The function of topo IIα in the development of mammalian cells has not been elucidated because of a lack of topo IIα mutants. Results: We generated mice with a targeted disruption of the topo IIα gene. The development of topo IIα-/- embryos was terminated at the 4- or 8-cell stage. When wild-type embryos at the 2- or 4-cell stage were treated with ICRF-193, a catalytic inhibitor of topo II, nuclear division occurred followed by cytokinesis to form 4 or 8 cells, respectively, then development was terminated. Microscope analysis of 4,6-diamidino-2-phenylindole (DAPI)-stained nuclei of both topo IIα-/- and ICFR-193-treated embryonic cells revealed a droplet-like structure connecting the terminals of two adjacent nuclei forming a bridge-like structure. Phosphorylated histone H3, a marker for the M phases, disappeared from the nuclei of the topo IIα-depleted embryonic cells. Laser scanning cytometry of the topo IIα-depleted cells revealed the presence of 2N DNA cells. Conclusions: Our results indicate that topo IIα has an essential role in the early stages of mouse development and that depletion of topo IIα from the embryonic cells causes incomplete nuclear division followed by enforced cytokinesis.