| Popis: |
The size distributions of randomly selected nuclei and of labelled nuclei were examined in livers of 10 g rats killed 3, 8 and 24 hours after injection of thymidine-3H. Randomly selected parenchymal liver nuclei of 10 g rats make up two populations with average diameters of 7.2 ± 0.4 μ and 8.6 ± 0.4 μ respectively; but the latter, larger nuclei constitute only 6.8% of the total. In contrast, 20.5 and 27.9% of the labelled nuclei seen 3 and 8 hours after thymidine-3H injection respectively were of this larger size, so that the proportion of large nuclei is several times higher among labelled than randomly selected nuclei. Since available evidence indicates that at these two time intervals, labelled nuclei are premitotic, it is suggested that there is nuclear enlargement prior to mitosis. While the nuclear enlargement is related to DNA synthesis, it takes place some time after this synthesis begins and proceeds gradually until the nucleus reaches a size comparable to that of permanently tetraploid nuclei. |
