Comparison of DNA polymerase activity and cell division in normal and delayed-implanting mouse embryos

✍ Scribed by Weitlauf, H. ;Kiessling, A. ;Buschman, R.

• Publisher: John Wiley and Sons
• Year: 1979
• Tongue: English
• Weight: 389 KB
• Volume: 209
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402090312

✦ Synopsis

Abstract

Cell division stops in mouse blastocysts during the prolonged, free‐living phase associated with delayed implantation. It is not known how the embryos are rendered mitotically dormant and then reactivated to implant at a later time, and the present experiments were undertaken to determine whether or not changes in the level of DNA polymerase in the embryos could play a role in the regulation of cell division.

Unattached normal and delayed‐implanting blastocycts were recovered from pregnant mice at intervals between the fourth and the fifteenth day of pregnancy, and the number of cells and amount of DNA polymerase in the embryos were determined in order to correlate amount of enzyme with the rate of cell division. The number of cells in both types of embryos increased equally until noon of day 5. However, as expected, the rate of cell division in the delayed implanting blastocysts then slowed and there was no further increase in the number of cells beyond day 7 or 8. Termination of the dormant phase of delayed implantation by the injection of 17 β‐estradiol, resulted in a resumption of cell division within 24 hours. The total amount of DNA polymerase activity in normal blastocysts increased 200% between day 4 and day 5. In contrast, there was only a 60% increase in enzyme activity in the delayed implanting embryos during this interval. The level of polymerase activity in the delayed implanting embryos then decreased and remained depressed for the several days of the dormant period. Injecting 17 β‐estradiol on day 9 resulted in an increase (120%) in polymerase activity. Although the amount of DNA polymerase per cell in the dormant embryos was low by comparison with that in normal embryos, it was higher than that in adult spleen (a tissue that is active in DNA synthesis) and therefore it appears likely that other mechanisms are involved in regulating cell division in the embryos.