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本帖最后由 tpwang 于 2011-6-30 21:37 编辑
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5 u/ z0 q8 H9 V5 K4 v. M回复 tpwang 的帖子
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重编程早期的细胞分裂过程补充材料。
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5 f" B+ [ o9 D/ ^! uJaenisch在2011年6月ISSCR会上的摘要其中一部分是关于重编程机制的:
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8 t" A$ R6 B }/ j6 O; ?2 e- Ia. Mechanisms of direct reprogramming:
+ ?/ E8 u; Q9 c9 B7 B6 e: pDirect reprogramming of somatic cells into induced pluripotent stem cells (iPSCs) can be achieved by over-expression of Oct4, Sox2, Klf4 and c-Myc transcription factors, but only a minority of donor somatic cells can be reprogrammed to pluripotency. We have demonstrated that reprogramming is a continuous stochastic process where almost all donor cells eventually give rise to iPSCs upon continued growth and transcription factor expression. Inhibition of the p53/p21 pathway or over expression of Lin28 increased the cell division rate and resulted in an accelerated kinetics of iPSC formation that was directly proportional to the increase in cell proliferation. These results suggest that the number of cell divisions is a key parameter driving epigenetic reprogramming to pluripotency. In contrast, Nanog over expression accelerated reprogramming in a predominantly cell division rate independent manner.. y# g M2 J/ f7 U
重编程过程早期的细胞分裂与增殖是一个必要的阶段，细胞染色质结构只有在分裂过程中才会留出机会发生改变（放松、开放），使得重编程因子有机会结合。p53抑制（减弱凋亡）等提升了细胞分裂速率从而加速了iPSC形成。而Nanog加速重编程的作用则与细胞分裂速率无关。
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亚马纳卡的摘要里也提到：
, }8 f5 x7 T6 B' v1 \' t. MIt is also important to note that an iPS cell clone can be heterogeneous despite the fact that all the cells within the clone are derived from a single progenitor cell. This is because the process requires multiple cell divisions which cannot be completed by the four exogenous factors alone. Additional factors including p53 and Rb pathways are considered to play various roles in achieving full reprogramming.
4 J" G2 p/ `' J# k8 G细胞分裂过程导致iPSC克隆的“非均一性”。另一个事情是考虑到早期的细胞分裂增殖，最后计算的重编程效率其实都是高估的，因为没有把增殖的因素考虑进去。
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V0 Y, E% E) | I5 w同在Reprogramming and Fate Conversion的session下，Gurdon关于核移植机制的讨论也涉及到早期的细胞分裂：6 ~. o! @ o9 Q
...the events that immediately follow the transplantation of somatic nuclei to eggs are difficult to analyze because, immediately after nuclear transfer to eggs, the major activity of a transplanted nucleus is to replicate DNA, and transcription starts only after many hours (mammals) or many cell divisions (amphibia). When somatic nuclei are transplanted to the germinal vesicle of an oocyte in first meiotic prophase, a very efficient activation of previously quiescent pluripotency genes takes place.
- O* i* e2 n6 Q$ N b6 \精确到特定细胞分裂阶段的核移植可以通过激活多能基因而提高核移植重编程效率。这种干预手段不知是否能在因子诱导的重编程中加以应用。
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8 {4 N" K) G2 d- r重编程过程中通过提高细胞分裂速率（无论通过主动还是被动的方法）来提高重编程效率，自然也同比例地（也许甚至是不成比例地）增加了风险，尤其是采用抑制细胞凋亡机制的手段。有可能存在欲速则不达的问题，不小心就确实成了造“潜在肿瘤干细胞”了。1 i4 @) O/ L$ o% M: H
1 W0 q& h, S9 e. m7 Z0 N一个连带的问题是重编程过程中的“mutations”是重编程的“推动者”还是“蹭车者”。Abstract里有一篇相关的内容：
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, Q2 L# N* K" E/ K( IFUNCTIONAL CONSEQUENCES OF SOMATIC MUTATIONS IN HUMAN INDUCED PLURIPOTENT STEM CELLS
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It is also unknown if mutations are functional “drivers” for the reprogramming process or if they are “passengers” acquired due to clonal selection. |
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发表于 2011-6-30 14:58
