Scherini E, Mares V
Department of Animal Physiology, University of Pavia, Italy.
Physiol Res. 1993;42(6):193-9.
3H thymidine was injected into pregnant mice in order to label the DNA in the dividing Purkinje cell (PC) precursors of the embryonic cerebellum. The retention of 3H-DNA was evaluated in PC nuclei of animals at the age of 25 days, 3, 6 or 9 months by light microscope autoradiography. The number of silver grains decreased in the whole nuclei by 13.6% and 19.6% in animals 6- and 9-month-old, respectively. In the nucleolar region, the loss of DNA radioactivity was more profound; the silver grain counts decreased by 22.6% and 29.1% in 6- and 9-month-old animals, respectively. No significant differences in the volume and dry mass concentration were found in the PC nuclei of 25 PD and 9 PM old animals. Therefore, the observed changes in grain density counts represent the actual measure of 3H-DNA loss, and/or "spontaneous" renewal of the DNA molecule in PC nuclei, as well as its higher expression in the nucleolar region. Furthermore, it follows from the comparison of our data with those present in the literature, that DNA synthesized in nerve cell precursors before their withdrawal from the mitotic cycle is more stable than that synthesized in postmitotic neurones. This suggests that the repair of DNA in mature neurones might be of an error-prone type.
将3H胸腺嘧啶核苷注射到怀孕小鼠体内，以便标记胚胎小脑浦肯野细胞（PC）前体中正在分裂的DNA。通过光学显微镜放射自显影术，在25天、3个月、6个月或9个月大的动物的PC细胞核中评估3H-DNA的保留情况。在6个月和9个月大的动物中，整个细胞核中的银颗粒数量分别减少了13.6%和19.6%。在核仁区域，DNA放射性的损失更为明显；在6个月和9个月大的动物中，银颗粒计数分别减少了22.6%和29.1%。在25日龄和9月龄动物的PC细胞核中，未发现体积和干质量浓度有显著差异。因此，观察到的颗粒密度计数变化代表了3H-DNA损失的实际测量值，和/或PC细胞核中DNA分子的“自发”更新，以及其在核仁区域的更高表达。此外，通过将我们的数据与文献中的数据进行比较可知，在神经细胞前体退出有丝分裂周期之前合成的DNA比在有丝分裂后神经元中合成的DNA更稳定。这表明成熟神经元中DNA的修复可能是易错类型的。
