Cell cycle analysis and X-chromosome inactivation in the developing mouse.

The duration of different phases of the cell cycle (G1, S, G2, and M), as well as the exact time of initiation of asynchronous DNA replication pattern in one of the X-chromosomes in the female mouse during the early stages of development, have been investigated. It was found that early developmental stages in the mouse are devoid of G1 period, and from the late blastocyst stage the embryonic cells first acquire all the characteristic stages of the cell cycle (G1, S, G2, and M). Additionally, asynchronous DNA replication pattern in one of the X-chromosomes in the female embryos was found to be initiated with the appearance of the G1 period. I have established a correlation between the onset of the G1 period and the initiation of an asynchronous DNA replication pattern in one of the X-chromosomes of the female mammal during embryogenesis.