美國(guó)斯坦福大學(xué)醫(yī)學(xué)院微生物與免疫學(xué)系，干細(xì)胞生物與再生醫(yī)學(xué)研究所,，Baxter干細(xì)胞生物實(shí)驗(yàn)室的科學(xué)家在iPS的研究上取得新的成果,，相關(guān)研究文章發(fā)表在Nature在線版上。
將疾病患者體細(xì)胞重排為病人特異性的誘導(dǎo)多能干細(xì)胞是再生醫(yī)學(xué)的一個(gè)新的創(chuàng)舉,。然而,，誘導(dǎo)iPS細(xì)胞一直存在很多技術(shù)上的瓶頸問題，這些瓶頸問題包括：體細(xì)胞重排的不一致性,，重排效率不高（＜0.1%）,，重排時(shí)間長(zhǎng)（2-3周），DNA去甲基化的問題,。
DNA甲基化是最早發(fā)現(xiàn)的修飾途徑之一,，大量研究表明，DNA甲基化能引起染色質(zhì)結(jié)構(gòu),、DNA構(gòu)象,、DNA穩(wěn)定性及DNA與蛋白質(zhì)相互作用方式的改變，從而控制基因表達(dá),。在甲基轉(zhuǎn)移酶的催化下,，DNA的CG兩個(gè)核苷酸的胞嘧啶被選擇性地添加甲基，形成5－甲基胞嘧啶,，這常見于基因的5'-CG-3'序列,。大多數(shù)脊椎動(dòng)物基因組DNA都有少量的甲基化胞嘧啶，主要集中在基因5＇端的非編碼區(qū),，并成簇存在,。甲基化位點(diǎn)可隨DNA的復(fù)制而遺傳，因?yàn)镈NA復(fù)制后,，甲基化酶可將新合成的未甲基化的位點(diǎn)進(jìn)行甲基化。DNA的甲基化可引起基因的失活,。
要讓體細(xì)胞重新恢復(fù)到未分化的狀態(tài)需要解決的一個(gè)問題就是DNA甲基化的問題,，所以說DNA去甲基化問題成為誘導(dǎo)iPS的一個(gè)重要難題。
為了研究iPS誘導(dǎo)過程中的相關(guān)機(jī)制,，Helen M. Blau院士領(lǐng)銜的研究小組構(gòu)建了一個(gè)異核體細(xì)胞（融合了小鼠胚胎干細(xì)胞和人類成纖維細(xì)胞）,，這種異核體誘導(dǎo)的速度比正常的體細(xì)胞誘導(dǎo)速度快很多，僅需1天時(shí)間,，誘導(dǎo)效率高達(dá)70%,。
用RNAi進(jìn)行掃描發(fā)現(xiàn)，異核體誘導(dǎo)啟動(dòng)依賴一種蛋白,，這種蛋白是AID（胞嘧啶核苷脫氨酶,，也稱為AICDA）,。AID不僅促進(jìn)細(xì)胞重排過程中的脫甲基作用，更是可以誘導(dǎo)OCT4和NANOG基因的表達(dá)（2種iPS誘導(dǎo)過程中的轉(zhuǎn)錄因子）,。AID蛋白對(duì)成纖維細(xì)胞上的OCT4與NANOG發(fā)揮作用,，對(duì)胚胎干細(xì)胞不發(fā)揮作用。
這些實(shí)驗(yàn)數(shù)據(jù)表明,，誘導(dǎo)哺乳動(dòng)物iPS需要AID蛋白參與啟動(dòng)細(xì)胞的DNA脫甲基化,，并啟動(dòng)細(xì)胞核重新編程過程。（生物谷Bioon.com）
干細(xì)胞研究
iPS研究
干細(xì)胞治療
生物谷推薦原始出處：
Nature advance online publication 21 December 2009 | doi:10.1038/nature08752
Reprogramming towards pluripotency requires AID-dependent DNA demethylationnear-final version
Nidhi Bhutani1,2, Jennifer J. Brady1,2, Mara Damian1, Alessandra Sacco1, Stéphane Y. Corbel1 & Helen M. Blau1
1 Baxter Laboratory for Stem Cell Biology, Institute for Stem Cell Biology and Regenerative Medicine, Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305-5175, USA
2 These authors contributed equally to this work.
3 Correspondence to: Helen M. Blau1 Correspondence and requests for materials should be addressed to H.B.
Reprogramming of somatic cell nuclei to yield induced pluripotent stem (iPS) cells makes possible derivation of patient-specific stem cells for regenerative medicine. However, iPS cell generation is asynchronous and slow (2–3?weeks), the frequency is low (<0.1%), and DNA demethylation constitutes a bottleneck. To determine regulatory mechanisms involved in reprogramming, we generated interspecies heterokaryons (fused mouse embryonic stem (ES) cells and human fibroblasts) that induce reprogramming synchronously, frequently and fast. Here we show that reprogramming towards pluripotency in single heterokaryons is initiated without cell division or DNA replication, rapidly (1?day) and efficiently (70%). Short interfering RNA (siRNA)-mediated knockdown showed that activation-induced cytidine deaminase (AID, also known as AICDA) is required for promoter demethylation and induction of OCT4 (also known as POU5F1) and NANOG gene expression. AID protein bound silent methylated OCT4 and NANOG promoters in fibroblasts, but not active demethylated promoters in ES cells. These data provide new evidence that mammalian AID is required for active DNA demethylation and initiation of nuclear reprogramming towards pluripotency in human somatic cells.
