克隆干细胞保真性更高

坤明

来源：生物谷 2014-07-04 15:35
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$ I+ F: t* N+ O4 p- o2014年7月4讯 /生物谷BIOON/ --与重编程的细胞相比，通过核移植产生的干细胞具有更高的保真性。& p  }8 P7 ]3 n) C, @

. Y. C$ A9 t' L. m) I, d! A人类的多功能干细胞首次在1998年从人类胚胎组织中培养获得。这种方法获得的干细胞仍然被作为多能干细胞评价的金标准，因为从胚胎组织中获得的干细胞毫无疑问可以产生各种类型的组织。7 x, L/ G  G# u$ l; o6 x

# L) u1 I$ Y) R* |% V) i4 H从一个人分化的细胞得到能形成各种细胞类型的干细胞有两种方法，一个是通过克隆，一个是通过重编程诱导多能干细胞（iPS细胞）。这些新技术都能从病人身上提取细胞并产生和病人不发生排斥的干细胞。* ?! N2 ^9 }) U3 ?* i

, ]( i( ~+ G0 X. b! _去年，Shoukhrat Mitalipov和他的团队第一个通过核移植技术获得了人的多能干细胞，这种技术更熟知的名字是克隆。他们通过将培养获得的皮肤细胞的细胞核放入未受精的去核卵细胞中，成功的获得了胚胎干细胞。
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而Mitalipov最近在Nature杂志上发表的结果称，他的团队比较了克隆得到的多能干细胞和诱导多能干细胞。将两种细胞的状态和之前多能干细胞的金标准作比较，通过比较细胞的甲基化类型，一种DNA的表观遗传修饰来确定两种细胞相对的质量。最终结果表明，多余1200个基因在这三种细胞中的表达不一致，其中65%的基因差异来自于iPS细胞和另外两种胚胎干细胞。这样的差异显示，通过核移植产生的胚胎干细胞在发育成为其他细胞类型方面iPS细胞有着明显的优势。

坤明

Pluripotent stem cells can produce large supplies of, say, neurons or heart muscle, so are valuable for studying diseases and, potentially, for treating them. Human pluripotent stem cells were first made2 in 1998 from embryos left over from fertility treatments, and pluripotent stem cells produced by this method are still considered the gold standard because there is no question that embryos can produce all types of tissue in the body.# d; b  S* p& R+ p: K/ x

' r- O1 z9 ?- v- b4 p  Y3 \# S& wThe newer techniques, called nuclear transfer and genetic reprogramming, can use cells from living people to make pluripotent stem cells that are genetically matched to a patient. For research purposes, matching provides cells from people whose disease history is known. For therapies, matching means that cells are more likely to be suitable for therapies.
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( _- R7 {. W6 _7 w9 x9 \$ JLast year, Shoukhrat Mitalipov, a cell biologist at the Oregon Health and Science University in Portland, and his colleagues became the first to produce human pluripotent stem cells using nuclear transfer3, a technique also known as cloning. They took the nucleus from a cultured skin cell, placed it in an unfertilized egg that had had its nucleus removed, then made embryonic stem (ES) cells from the resultant embryo.
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  ~2 }/ e$ ]/ Q6 J8 ^6 FIn the paper published today, Mitalipov and his collaborators compared cloned ES cells to 'induced pluripotent' stem (iPS) cells made by inserting 'reprogramming' genes into cells from the same batch of cultured skin cells used to make the cloned ES cells.& g" Z8 L2 w* d! A

0 _; G  n0 C* B8 r# [* CIn neither case did the genetic material return fully to an embryonic-like state, says Mitalipov, but one technique was the clear winner. "Nuclear transfer doesn't do a perfect job of resetting, but in general it does a very, very good job in relation to iPS reprogramming."
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To measure the relative quality of the two types directly, they saw how they measured next to the 'golden standard' of cells from discarded embryos by looking at their patterns of methylation, a type of 'epigenetic' modification of DNA, meaning that it affects gene expression without changing the underlying gene sequences.
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1 j8 t( b8 ^" c$ l& k8 rMethylation patterns of nuclear-transfer ES cells were closer to those from fertilized eggs than were methylation patterns in iPS cells. More than 1,200 genes were expressed differently in the three cell types; most of these differences, about 65%, were between iPS cells and the two types of ES cells. These differences, says Mitalipov, could mean that ES cells from nuclear transfer are better able than iPS cells to mature into other cell types.
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"It's an important study. It points to some clear differences," says Martin Pera, a stem-cell biologist studying pluripotency at the University of Melbourne in Australia. However, he says, much more work remains to be done. Epigenetic modifications of iPS cells sometimes grow more like those of ES cells over a longer time in culture, for example, and it is unclear whether the differences spotted by Mitalipov and his team will matter once the stem cells have been coaxed into specialized types.1 b; y0 a4 E! S% W1 r
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Genetic reprogramming is likely to remain the dominant technique for making new pluripotent cells, says Pera. Nuclear transfer is ethically, logistically and technically more difficult. It requires young women to provide eggs and creates an embryo that is then destroyed for research. (Mitalipov and his collaborators needed their institutions' approval and special funding sources to work on the cells.) The nuclear-transfer technique also requires several months of training.
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* {9 N# r" M# wStill, such studies are warranted, says Pera, because understanding how an egg cell resets a transferred cell's nucleus into an embryonic-like state would solve a big biological mystery and might help to improve techniques for creating pluripotent cells. "As we see these differences, we may get clues on how to modify the iPS process to get greater fidelity with ES cells."

zhouleiwang2

对于说成体细胞核移植（SCNT或曰克隆）得到的干细胞而言，要说起不会与提供细胞核的个体发生免疫排斥，恐怕是一个有些以偏概全的说法。能够提供卵子的是女性，细胞质遗传物质来自女性，因此得到的干细胞的表达的部分蛋白质必然会与男性个体的体细胞会有差异，这些蛋白质就是潜在的免疫原吧。

dispassion

我总感觉这种通过建立的细胞系，说一种方法比另一种方法好的实验不是很确信。因为建立的细胞系本身（包括人的干细胞作为的正对照）就会因为不同操作，不同检测标准在多能性上有所差别。但是又想不到更好的比较两种诱导方法区别的方法。期待大家的指导。