Enforced cytokinesis without complete nuclear division in embryonic cells depleting the activity of DNA topoisomerase IIalpha.
BACKGROUND
There are two distinct DNA topoisomerase II (topo II) isoforms, designated topo IIalpha and topo IIbeta, in mammalian cells. The function of topo IIalpha in the development of mammalian cells has not been elucidated because of a lack of topo IIalpha mutants.


RESULTS
We generated mice with a targeted disruption of the topo IIalpha gene. The development of topo IIalpha-/- 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 IIalpha-/- 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 IIalpha-depleted embryonic cells. Laser scanning cytometry of the topo IIalpha-depleted cells revealed the presence of 2N DNA cells.


CONCLUSIONS
Our results indicate that topo IIalpha has an essential role in the early stages of mouse development and that depletion of topo IIalpha from the embryonic cells causes incomplete nuclear division followed by enforced cytokinesis.
Akimitsu
Nobuyoshi
N
Laboratory of Developmental Biochemistry, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 3-1, 7-Chome, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Adachi
Noritaka
N
Hirai
Hiroshi
H
Hossain
Muktadir S
MS
Hamamoto
Hiroshi
H
Kobayashi
Masao
M
Aratani
Yasuaki
Y
Koyama
Hideki
H
Sekimizu
Kazuhisa
K
D000818:Animals; D000951:Antigens, Neoplasm; D001755:Blastocyst / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D002455:Cell Division / Q000187:drug effects*; D002467:Cell Nucleus / Q000187:drug effects* / Q000378:metabolism; D004261:DNA Replication / Q000187:drug effects*; D004250:DNA Topoisomerases, Type II / Q000172:deficiency* / Q000378:metabolism; D004268:DNA-Binding Proteins; D054659:Diketopiperazines; D006657:Histones / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008938:Mitosis / Q000187:drug effects; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology; D059005:Topoisomerase II Inhibitors
D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D054659:Diketopiperazines; D006657:Histones; D010879:Piperazines; D059005:Topoisomerase II Inhibitors; C070899:4,4'-(1,2-dimethyl-1,2-ethanediyl)bis-2,6-piperazinedione; D004250:DNA Topoisomerases, Type II