Human Reproduction, Vol 13, 398-402, Copyright © 1998 by Oxford University Press
H Matsumoto and S Sugawara
Development of the rat embryo is arrested at the 2-cell stage in vitro in
the presence of inorganic phosphate (Pi). Rat embryos were affected by
exposure to 1.19 mM KH2PO4 in modified hamster embryo culture medium- 1 at
the late 2-cell stage only. When exposure durations were 6 h, embryos whose
exposure timings were prior to cleavage had a reduced rate of development
to the blastocyst stage (2-8%) when compared with embryos with no exposure
to Pi (97%, P < 0.05). When exposure durations were 18 h, all embryos
were arrested at the 2- to 4-cell stage. These timings would correspond to
the G2 to M phase of the second cell cycle. Maturation-promoting factor
(MPF), which is regulated by a phosphorylation cascade, controls cell
division, and its kinase activity is necessary in order for the cell to
enter the M phase. However, the histone H1 kinase activity levels and the
patterns of the state of phosphorylation of cdc2 were the same in blocked
and non- blocked embryos. Because MPF was active in blocked embryos, the
developmental block in rat 2-cell embryos caused by phosphate was not due
to MPF activity or its phosphorylation cascade.
ARTICLES
Effect of phosphate on the second cleavage division of the rat embryo
Department of Animal Sciences, Tohoku University, Sendai, Japan.
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