Mills J C, Kim L H, Pittman R N
Cell Biology Graduate Group, School of Medicine, University of Pennsylvania, Philadelphia 19104, USA.
Exp Cell Res. 1997 Mar 15;231(2):337-45. doi: 10.1006/excr.1997.3474.
Long-term timelapse videomicroscopy was used to investigate the relationships and transitions between mitosis, differentiation, and apoptosis in cultures of NGF-differentiated PC12 cells. After 4 days in NGF, cultures were at an early stage of neuronal differentiation. Removal of NGF led to an appreciable increase in apoptosis with no effect on the relatively high mitotic rate. After 7 days in NGF, cells were more neuronal; NGF withdrawal again resulted in no change in the low mitotic rate but an even greater increase in apoptosis, eventually leading to considerable net loss of cells. After 10 days, cells were terminally differentiated; removal of NGF did not affect the negligible mitotic rate but induced a dramatic increase in apoptosis resulting in death of most of the cells. Apoptosis in the fraction of cells that had become NGF-dependent followed a similar timecourse and was characterized by the same morphology at all three differentiation states. Thus, acquisition of NGF-dependence in PC12 cultures seemed to be the result of a steadily increasing percentage of cells that had each undergone a relatively rapid transition to a postmitotic, NGF-sensitive state. These studies were also helpful for elucidating the timing of apoptosis. Onset of apoptosis was markedly asynchronous within a culture, but the active, blebbing phase, once initiated, always lasted about 45 min, regardless of differentiation state or time spent without NGF. Thus, the active phase might represent a conserved sequence of events that every cell must ultimately undergo before apoptotic death.
利用长期延时视频显微镜技术研究了神经生长因子（NGF）分化的PC12细胞培养物中，有丝分裂、分化和凋亡之间的关系及转变。在NGF作用4天后，培养物处于神经元分化的早期阶段。去除NGF导致凋亡显著增加，而对相对较高的有丝分裂率没有影响。在NGF作用7天后，细胞更具神经元特性；再次去除NGF导致低有丝分裂率没有变化，但凋亡进一步大幅增加，最终导致细胞大量净损失。10天后，细胞终末分化；去除NGF不影响可忽略不计的有丝分裂率，但诱导凋亡急剧增加，导致大多数细胞死亡。已对NGF产生依赖的那部分细胞的凋亡遵循相似的时间进程，并且在所有三种分化状态下具有相同的形态特征。因此，PC12培养物中对NGF依赖性的获得似乎是由于经历了相对快速转变至有丝分裂后、对NGF敏感状态的细胞百分比稳步增加的结果。这些研究对于阐明凋亡的时间也有帮助。培养物中凋亡的起始明显不同步，但一旦启动，活跃的出泡阶段总是持续约45分钟，无论分化状态或无NGF的时间长短。因此，活跃阶段可能代表了每个细胞在凋亡死亡前最终必须经历的一系列保守事件。
