世界生命科學(xué)前沿動(dòng)態(tài)周報(bào)（三十六）

（12.13-12.19/2010）
美寶國(guó)際集團(tuán):陶國(guó)新 

 　　本周動(dòng)態(tài)包括以下內(nèi)容：人體多能干細(xì)胞體外定向分化形成腸組織；CRTC3基因可放慢脂肪消耗速度；發(fā)現(xiàn)能顯著減緩生物鐘的化合物；降低基質(zhì)與細(xì)胞的機(jī)械力可使干細(xì)胞保持在多能狀態(tài)；p53失活使癌細(xì)胞獲得干細(xì)胞特性；果蠅生殖干細(xì)胞分化新機(jī)制。

1. 人體多能干細(xì)胞體外定向分化形成腸組織
【摘要】
　　據(jù)美國(guó)物理學(xué)家組織網(wǎng)12月13日?qǐng)?bào)道，美國(guó)科學(xué)家首次在實(shí)驗(yàn)室中將人體多能干細(xì)胞變成了功能性的人體腸道組織。辛辛那提兒童醫(yī)院醫(yī)學(xué)中心的科學(xué)家在12日出版的《自然》雜志在線版上表示，最新突破為人體腸道的發(fā)育、功能和有關(guān)疾病的研究打開(kāi)了一扇大門，并有望研制出用于移植的腸道組織。該研究主要負(fù)責(zé)人、辛辛那提兒童醫(yī)院發(fā)育生物學(xué)分部高級(jí)研究員詹姆斯·威爾斯表示，這是科學(xué)家首次證明，皮氏培養(yǎng)皿（用作細(xì)菌培養(yǎng)的有蓋玻璃碟）中人體多功能干細(xì)胞能轉(zhuǎn)變?yōu)榫哂腥S架構(gòu)、細(xì)胞組成成分同人體腸組織非常類似的人體組織。將干細(xì)胞變成腸道組織最終會(huì)讓罹患?jí)乃佬孕∧c結(jié)腸炎、炎性腸病、短腸綜合征的病人大大受益。
　　威爾斯團(tuán)隊(duì)在研究中使用了兩類多功能干細(xì)胞：來(lái)自于幾個(gè)月大的人體胚胎干細(xì)胞（hESCs）和基于人體皮膚細(xì)胞的誘導(dǎo)多功能干細(xì)胞（iPSCs）。hESCs能變?yōu)槿梭w內(nèi)200多種細(xì)胞類型中的任何一種，因此也被稱為多功能干細(xì)胞。iPSCs可以使用病人的細(xì)胞來(lái)獲得，因擁有該病人的遺傳成分而不會(huì)發(fā)生排斥反應(yīng)。威爾斯解釋到，因?yàn)閕PSCs技術(shù)非常新穎，其是否具有hESCs所擁有的全部潛能還是未解之謎，因此，研究人員在本次實(shí)驗(yàn)中使用了這兩種干細(xì)胞，以進(jìn)一步測(cè)試和比較這兩種干細(xì)胞轉(zhuǎn)化為其他細(xì)胞的能力。為了將多功能干細(xì)胞變成腸道組織，科學(xué)家使用化學(xué)物質(zhì)和生長(zhǎng)因子蛋白進(jìn)行了一系列細(xì)胞操作，在實(shí)驗(yàn)室中模擬出了胚胎腸的發(fā)育過(guò)程?？茖W(xué)家首先將多功能干細(xì)胞變成名為定型內(nèi)胚層的胚胎細(xì)胞，接著將胚胎細(xì)胞變成了名為“后腸定向祖細(xì)胞”的胚胎腸細(xì)胞。隨后，他們將胚胎腸細(xì)胞提交給促進(jìn)腸發(fā)育的“親腸”細(xì)胞培養(yǎng)裝置。28天后，科學(xué)家獲得了類似于胎兒腸的成型三維組織，這種組織包含腸道所有的主要細(xì)胞，包括腸上皮細(xì)胞、帕內(nèi)特細(xì)胞和腸內(nèi)分泌細(xì)胞。這個(gè)組織會(huì)持續(xù)成熟，獲得正常人體腸組織擁有的吸收和分泌功能，并會(huì)形成腸特異性干細(xì)胞。
　　威爾斯表示，這個(gè)過(guò)程可以作為人體腸發(fā)育的研究工具，也可幫助科學(xué)家了解人體腸道在生病后的變化。由于大部分口服藥都通過(guò)腸道吸收發(fā)揮作用，該突破還將有助于科學(xué)家設(shè)計(jì)出更好的、更容易吸收的口服藥物。研究人員接下來(lái)將進(jìn)行動(dòng)物實(shí)驗(yàn)，驗(yàn)證該腸組織是否可以有效地用于移植手術(shù)中，并最終用來(lái)治療罹患腸道疾病的病人。

【點(diǎn)評(píng)】
　　通過(guò)模擬胚胎腸發(fā)育體外培養(yǎng)干細(xì)胞發(fā)育形成有一定功能的腸組織，是干細(xì)胞生物學(xué)向具有實(shí)際應(yīng)用價(jià)值的方向邁出的重要一步，盡管依然受限于胚胎干細(xì)胞和誘導(dǎo)多能干細(xì)胞的來(lái)源和質(zhì)量。

【原文摘錄】Nature doi:10.1038/nature09691
Directed differentiation of human pluripotent stem cells into intestinal tissue in vitro
Jason R. Spence, Christopher N. Mayhew, Scott A. Rankin, et al.
Studies in embryonic development have guided successful efforts to direct the differentiation of human embryonic and induced pluripotent stem cells (PSCs) into specific organ cell types in vitro1, 2. For example, human PSCs have been differentiated into monolayer cultures of liver hepatocytes and pancreatic endocrine cells3, 4, 5, 6 that have therapeutic efficacy in animal models of liver disease7, 8 and diabetes9, respectively. However, the generation of complex three-dimensional organ tissues in vitro remains a major challenge for translational studies. Here we establish a robust and efficient process to direct the differentiation of human PSCs into intestinal tissue in vitro using a temporal series of growth factor manipulations to mimic embryonic intestinal development10. This involved activin-induced definitive endoderm formation11, FGF/Wnt-induced posterior endoderm pattering, hindgut specification and morphogenesis12, 13, 14, and a pro-intestinal culture system15, 16 to promote intestinal growth, morphogenesis and cytodifferentiation. The resulting three-dimensional intestinal ‘organoids’ consisted of a polarized, columnar epithelium that was patterned into villus-like structures and crypt-like proliferative zones that expressed intestinal stem cell markers17. The epithelium contained functional enterocytes, as well as goblet, Paneth and enteroendocrine cells. Using this culture system as a model to study human intestinal development, we identified that the combined activity of WNT3A and FGF4 is required for hindgut specification whereas FGF4 alone is sufficient to promote hindgut morphogenesis. Our data indicate that human intestinal stem cells form de novo during development. We also determined that NEUROG3, a pro-endocrine transcription factor that is mutated in enteric anendocrinosis18, is both necessary and sufficient for human enteroendocrine cell development in vitro. PSC-derived human intestinal tissue should allow for unprecedented studies of human intestinal development and disease.

2. CRTC3基因可放慢脂肪消耗速度
【摘要】 來(lái)源：新華網(wǎng) 發(fā)布時(shí)間：2010-12-17 11:18:28
　　為什么一些人竭力控制飲食依然肥胖？為什么一些人吃得不少照樣苗條？答案可能在基因中。美國(guó)一個(gè)研究小組發(fā)現(xiàn)，一種名為CRTC3的基因可以放慢脂肪消耗速度。人體若缺乏這種基因，則脂肪消耗快，不容易發(fā)胖。索爾克生物研究所生物學(xué)家馬克·蒙特米尼帶領(lǐng)的研究小組發(fā)現(xiàn)，普通老鼠和喪失CRTC3基因的老鼠正常進(jìn)食時(shí)，兩者體重未發(fā)生明顯變化。但喂它們吃高熱量飲食后，只有正常老鼠發(fā)胖。另外，喪失CRTC3基因的老鼠棕色脂肪細(xì)胞數(shù)量是普通老鼠的兩倍。棕色脂肪細(xì)胞燃燒白色脂肪細(xì)胞中的脂肪，產(chǎn)生熱量，維持動(dòng)物體溫。一些研究顯示，身材偏瘦者棕色脂肪細(xì)胞含量高于偏胖者。蒙特米尼告訴每日科學(xué)網(wǎng)站：“CRTC3可能是控制棕色脂肪細(xì)胞數(shù)量的開(kāi)關(guān)，如果能產(chǎn)生更多棕色脂肪細(xì)胞，就可能控制肥胖?！毖芯咳藛T比較兩組墨西哥裔美國(guó)人的體重后發(fā)現(xiàn)，CRTC3基因活躍的一組偏胖。
　　蒙特米尼分析，人類在進(jìn)化過(guò)程中，發(fā)展出應(yīng)對(duì)饑餓的機(jī)制，即經(jīng)由CRTC3這類基因的表達(dá)，放慢燃燒脂肪的速度。這種機(jī)制對(duì)人類祖先意義重大，因?yàn)樗麄兺燥栆活D要等好長(zhǎng)一段時(shí)間才能獵取到下頓食物，需要在身體內(nèi)存貯熱量。那些體內(nèi)“省吃基因”活躍的人具有生存優(yōu)勢(shì)，可以長(zhǎng)時(shí)間不吃東西存活。對(duì)現(xiàn)代人而言，這種機(jī)制可能是一種累贅，可能導(dǎo)致脂肪在體內(nèi)堆積，威脅健康。科學(xué)家上世紀(jì)60年代就想到人體內(nèi)可能存在“省吃基因”，當(dāng)時(shí)對(duì)基因的認(rèn)識(shí)遠(yuǎn)不如現(xiàn)在。
 　　蒙特米尼帶領(lǐng)的研究小組希望他們的發(fā)現(xiàn)給治療肥胖癥、減少人們患糖尿病等疾病風(fēng)險(xiǎn)開(kāi)拓一條新路?；谶@項(xiàng)研究，制藥企業(yè)可以開(kāi)發(fā)藥物抑制CRTC3基因的作用。醫(yī)生可以從一個(gè)人體內(nèi)CRTC3基因活躍程度掌握這個(gè)人患肥胖癥風(fēng)險(xiǎn)是否偏高，從而采取應(yīng)對(duì)措施。并非所有體內(nèi)CRTC3基因活躍的人都趨向發(fā)胖，例如，研究人員未發(fā)現(xiàn)這種基因與美國(guó)白人體重之間存在關(guān)聯(lián)。研究人員認(rèn)為，生活環(huán)境和生活方式同樣會(huì)影響體重。蒙特米尼說(shuō)：“治療糖尿病或肥胖癥的方法應(yīng)該因人而異。”每日科學(xué)網(wǎng)站的數(shù)據(jù)顯示，7200萬(wàn)美國(guó)成年人受肥胖癥困擾。

【點(diǎn)評(píng)】
基因?qū)Ψ逝值挠绊懸欢ù嬖?，但不是全部，而且因人而異，后天的環(huán)境影響也不可小覷。

【原文摘錄】Nature 468: 933–939， doi:10.1038/nature09564
CRTC3 links catecholamine signalling to energy balance
Youngsup Song, Judith Altarejos, Mark O. Goodarzi, et al.
The adipose-derived hormone leptin maintains energy balance in part through central nervous system-mediated increases in sympathetic outflow that enhance fat burning. Triggering of β-adrenergic receptors in adipocytes stimulates energy expenditure by cyclic AMP (cAMP)-dependent increases in lipolysis and fatty-acid oxidation. Although the mechanism is unclear, catecholamine signalling is thought to be disrupted in obesity, leading to the development of insulin resistance. Here we show that the cAMP response element binding (CREB) coactivator Crtc3 promotes obesity by attenuating β-adrenergic receptor signalling in adipose tissue. Crtc3 was activated in response to catecholamine signals, when it reduced adenyl cyclase activity by upregulating the expression of Rgs2, a GTPase-activating protein that also inhibits adenyl cyclase activity. As a common human CRTC3 variant with increased transcriptional activity is associated with adiposity in two distinct Mexican-American cohorts, these results suggest that adipocyte CRTC3 may play a role in the development of obesity in humans.

3. 發(fā)現(xiàn)能顯著減緩生物鐘的化合物
【摘要】 中國(guó)日?qǐng)?bào)網(wǎng) 發(fā)布時(shí)間：2010-12-17 12:29:44
　　據(jù)美國(guó)物理學(xué)家組織網(wǎng)12月14日?qǐng)?bào)道，美國(guó)研究人員在使用自動(dòng)篩選技術(shù)尋找新藥品時(shí)，發(fā)現(xiàn)了一種能顯著減緩生物鐘的分子化合物，將其命名為“白日罪惡”。這一發(fā)現(xiàn)有望被用來(lái)開(kāi)發(fā)新藥品，幫助需要倒時(shí)差的空中飛人和嚴(yán)重睡眠障礙患者。相關(guān)論文發(fā)表于《公共科學(xué)圖書館—生物學(xué)》（PLoS Biology）。
　　此項(xiàng)研究由美國(guó)加利福尼亞大學(xué)圣地亞哥分校生物科學(xué)院院長(zhǎng)史蒂夫·凱的實(shí)驗(yàn)室主導(dǎo)。實(shí)驗(yàn)中，他們將生物鐘基因加入到可使螢火蟲發(fā)光的熒光素酶基因中，然后將其植入人的骨癌細(xì)胞中，這樣骨癌細(xì)胞就可以在生物鐘被激活時(shí)發(fā)光，從而可以直觀地得知細(xì)胞生物鐘的變化。在觀察了多達(dá)12萬(wàn)種可能的化合物與人類骨癌細(xì)胞發(fā)生的反應(yīng)后，研究人員篩選出了“白日罪惡”。在老鼠和幼年斑馬魚身上，研究人員同樣發(fā)現(xiàn)這種分子化合物能顯著減慢它們的生物鐘。之后，史蒂夫的團(tuán)隊(duì)將隔離出的“白日罪惡”分子交給另一間實(shí)驗(yàn)室的科學(xué)家做進(jìn)一步研究，也得出了同樣的結(jié)論。有鑒于此，史蒂夫自信地表示：“從理論上來(lái)說(shuō)，‘白日罪過(guò)’可以用于治療睡眠障礙?！?

【點(diǎn)評(píng)】
　　影響生物鐘基因的化合物既可能治療睡眠障礙，也可能擾亂生物節(jié)律，作為人工干預(yù)基因活動(dòng)的后果人類還沒(méi)有把握完全掌控。

【原文摘錄】PLoS Biol 8(12): e1000559 doi:10.1371/journal.pbio.1000559
High-Throughput Chemical Screen Identifies a Novel Potent Modulator of Cellular Circadian Rhythms and Reveals CKIa as a Clock Regulatory Kinase
Hirota T, Lee JW, Lewis WG, et al.
The circadian clock underlies daily rhythms of diverse physiological processes, and alterations in clock function have been linked to numerous pathologies. To apply chemical biology methods to modulate and dissect the clock mechanism with new chemical probes, we performed a circadian screen of ~120,000 uncharacterized compounds on human cells containing a circadian reporter. The analysis identified a small molecule that potently lengthens the circadian period in a dose-dependent manner. Subsequent analysis showed that the compound also lengthened the period in a variety of cells from different tissues including the mouse suprachiasmatic nucleus, the central clock controlling behavioral rhythms. Based on the prominent period lengthening effect, we named the compound longdaysin. Longdaysin was amenable for chemical modification to perform affinity chromatography coupled with mass spectrometry analysis to identify target proteins. Combined with siRNA-mediated gene knockdown, we identified the protein kinases CKIδ, CKIα, and ERK2 as targets of longdaysin responsible for the observed effect on circadian period. Although individual knockdown of CKIδ, CKIα, and ERK2 had small period effects, their combinatorial knockdown dramatically lengthened the period similar to longdaysin treatment. We characterized the role of CKIα in the clock mechanism and found that CKIα-mediated phosphorylation stimulated degradation of a clock protein PER1, similar to the function of CKIδ. Longdaysin treatment inhibited PER1 degradation, providing insight into the mechanism of longdaysin-dependent period lengthening. Using larval zebrafish, we further demonstrated that longdaysin drastically lengthened circadian period in vivo. Taken together, the chemical biology approach not only revealed CKIα as a clock regulatory kinase but also identified a multiple kinase network conferring robustness to the clock. Longdaysin provides novel possibilities in manipulating clock function due to its ability to simultaneously inhibit several key components of this conserved network across species.

4. 降低基質(zhì)與細(xì)胞的機(jī)械力可使干細(xì)胞保持在多能狀態(tài)
【摘要】 Sciencedaily  2010-12-17 9:31:11
　　近日伊利諾大學(xué)的研究人員發(fā)現(xiàn)了一種新方法可使干細(xì)胞長(zhǎng)期維持在中間狀態(tài)。研究論文發(fā)表在 PLoS One雜志上。在論文中研究人員稱他們利用一種軟凝膠培養(yǎng)小鼠胚胎干細(xì)胞(mESCs)可使細(xì)胞長(zhǎng)期維持在多能狀態(tài)。并且無(wú)需加入昂貴的生長(zhǎng)因子，這種軟基質(zhì)能在很長(zhǎng)一段時(shí)間內(nèi)維持同質(zhì)克隆的生長(zhǎng)?！斑@一技術(shù)在未來(lái)的再生醫(yī)學(xué)中有著巨大的應(yīng)用前景，”研究的共同負(fù)責(zé)人、醫(yī)學(xué)科學(xué)和工程學(xué)教授Ning Wang說(shuō)：“這是一個(gè)鼓舞人心的結(jié)果。我們的研究結(jié)果表明我們朝著揭示干細(xì)胞的基本生物學(xué)邁出了重要的一步?！?BR>　　在干細(xì)胞研究中將mESC維持在均一的多能狀態(tài)是一件非常困難的事情。多能干細(xì)胞可自發(fā)地分化，轉(zhuǎn)變?yōu)閷ｉT化的組織類型例如皮膚或肌肉。長(zhǎng)期以來(lái)研究人員都是利用生長(zhǎng)因子來(lái)維持mESCs的狀態(tài)不變，但是即便如此不久之后培養(yǎng)細(xì)胞還是會(huì)進(jìn)入不同的分化階段，呈現(xiàn)不同的基因表達(dá)和形態(tài)。樣品的多樣性使得研究人員很難開(kāi)展實(shí)驗(yàn)誘導(dǎo)干細(xì)胞培養(yǎng)生成特定類型的組織?！拔覀兊哪繕?biāo)就是使同質(zhì)的未分化細(xì)胞朝著我們感興趣的組織分化，并且一直使這些細(xì)胞保持同質(zhì)性，”伊利諾大學(xué)基因組生物學(xué)研究所的動(dòng)物科學(xué)教授Tanaka說(shuō)：“只有如此，才能生成特定的細(xì)胞類型，并最終實(shí)現(xiàn)多能干細(xì)胞的臨床應(yīng)用?！?BR>　　在新研究中研究人員發(fā)現(xiàn)多能mESCs更傾向于粘附在一起形成圓形克隆，而克隆邊緣與堅(jiān)硬的培養(yǎng)皿接觸的細(xì)胞則相對(duì)分化地更快一些?；诖爽F(xiàn)象，研究人員決定將研究方向集中到mESC的機(jī)械學(xué)而非化學(xué)研究上。進(jìn)而研究人員發(fā)現(xiàn)相對(duì)于成熟的細(xì)胞干細(xì)胞要柔軟10倍，于是研究人員開(kāi)始質(zhì)疑是否是培養(yǎng)皿和細(xì)胞間的機(jī)械力刺激了細(xì)胞分化。在早期的研究中王寧和Tanaka證實(shí)即使是很小的機(jī)械力也可直接影響細(xì)胞的分化。那么是否可以利用機(jī)械學(xué)來(lái)抑制干細(xì)胞分化呢？研究人員大膽地提出了假設(shè)。
　　研究小組將培養(yǎng)的mESCs細(xì)胞分成三個(gè)處理組進(jìn)行平行試驗(yàn)：第一組mESCs細(xì)胞的用常規(guī)的加入生長(zhǎng)因子的培養(yǎng)基培養(yǎng)；研究人員將第二組細(xì)胞接種在與細(xì)胞同樣硬度的軟膠上培養(yǎng)，并加入生長(zhǎng)因子；第三組的細(xì)胞同樣在軟膠上培養(yǎng)，但卻沒(méi)有加入生長(zhǎng)因子。研究人員發(fā)現(xiàn)在軟凝膠上培養(yǎng)的細(xì)胞表現(xiàn)出更強(qiáng)的同質(zhì)性和多能性。甚至在缺乏因子因子的條件下，培養(yǎng)三個(gè)月，傳代20次后仍是如此。“世界上的事物都有兩面性。我們?cè)诎l(fā)現(xiàn)機(jī)械力可以誘導(dǎo)干細(xì)胞分化后反其道行之，證實(shí)降低基質(zhì)與細(xì)胞的機(jī)械力可使細(xì)胞保持在多能狀態(tài)，”王寧說(shuō)：“我們的研究證實(shí)機(jī)械環(huán)境具有與化學(xué)生長(zhǎng)因子一樣重要的作用。在體內(nèi)，細(xì)胞只在一段短時(shí)間內(nèi)分泌生長(zhǎng)因子。而另一方面，機(jī)械力則一直在影響著每個(gè)細(xì)胞?！痹诮酉聛?lái)的試驗(yàn)中，研究人員想嘗試用誘導(dǎo)多能干細(xì)胞(iPSCs)來(lái)進(jìn)一步驗(yàn)證他們的軟基質(zhì)培養(yǎng)方法“我們將嘗試將小鼠iPSCs接種到同樣的軟基質(zhì)中培養(yǎng)，看看是否能夠獲得同質(zhì)的干細(xì)胞培養(yǎng)物。這一實(shí)驗(yàn)如果能取得成功，其產(chǎn)生的影響將無(wú)疑是巨大的?！?Tanaka說(shuō)。

【點(diǎn)評(píng)】
　　通過(guò)控制物理作用的影響極大的改進(jìn)了干細(xì)胞培養(yǎng)的方法，對(duì)于大量獲得處于多能狀態(tài)的干細(xì)胞有很大幫助，有利于促進(jìn)干細(xì)胞的基礎(chǔ)研究。

【原文摘錄】PLoS ONE   doi:10.1371/journal.pone.0015655
Soft Substrates Promote Homogeneous Self-Renewal of Embryonic Stem Cells via Downregulating Cell-Matrix Tractions
Farhan Chowdhury, Yanzhen Li, Yeh-Chuin Poh, et al.
Maintaining undifferentiated mouse embryonic stem cell (mESC) culture has been a major challenge as mESCs cultured in Leukemia Inhibitory Factor (LIF) conditions exhibit spontaneous differentiation, fluctuating expression of pluripotency genes, and genes of specialized cells. Here we show that, in sharp contrast to the mESCs seeded on the conventional rigid substrates, the mESCs cultured on the soft substrates that match the intrinsic stiffness of the mESCs and in the absence of exogenous LIF for 5 days, surprisingly still generated homogeneous undifferentiated colonies, maintained high levels of Oct3/4, Nanog, and Alkaline Phosphatase (AP) activities, and formed embryoid bodies and teratomas efficiently. A different line of mESCs, cultured on the soft substrates without exogenous LIF, maintained the capacity of generating homogeneous undifferentiated colonies with relatively high levels of Oct3/4 and AP activities, up to at least 15 passages, suggesting that this soft substrate approach applies to long term culture of different mESC lines. mESC colonies on these soft substrates without LIF generated low cell-matrix tractions and low stiffness. Both tractions and stiffness of the colonies increased with substrate stiffness, accompanied by downregulation of Oct3/4 expression. Our findings demonstrate that mESC self-renewal and pluripotency can be maintained homogeneously on soft substrates via the biophysical mechanism of facilitating generation of low cell-matrix tractions.

5. p53失活使癌細(xì)胞獲得干細(xì)胞特性
【摘要】
　　p53是人類重要的腫瘤抑制基因，正常p53的生物功能好似“基因組衛(wèi)士”,在G1期檢查DNA損傷點(diǎn)，監(jiān)視基因組的完整性。當(dāng)基因組遭受損傷時(shí)，p53蛋白可阻止DNA復(fù)制，以提供足夠的時(shí)間使損傷DNA修復(fù)；如果修復(fù)失敗，p53蛋白則會(huì)引發(fā)細(xì)胞凋亡。當(dāng)p53基因的兩個(gè)拷貝都發(fā)生突變時(shí)，細(xì)胞的增殖會(huì)失去控制，從而導(dǎo)致細(xì)胞癌變。近日來(lái)自薩克生物研究學(xué)院和普林斯頓大學(xué)高級(jí)研究所的研究人員在共同合作的一項(xiàng)研究中發(fā)現(xiàn)p53還可抑制癌細(xì)胞向更富于侵襲性的干細(xì)胞樣狀態(tài)轉(zhuǎn)化。研究人員根據(jù)p53的這個(gè)新功能將其稱之為“防止基因組重編程的衛(wèi)士（Guardian against Genome Reprogramming）”。研究論文發(fā)表在本周的 PNAS 雜志上?！氨娝苤头只?、細(xì)胞及遺傳異質(zhì)性是許多侵襲性和致死性癌癥的重要特征，”薩克生物研究所基因表達(dá)實(shí)驗(yàn)室的Wahl教授說(shuō)道：“最近有科學(xué)家提出這些特征是由于存在干細(xì)胞樣癌細(xì)胞所致。我們的發(fā)現(xiàn)表明p53突變可使腫瘤細(xì)胞重新獲得干細(xì)胞樣‘編程’?！薄鞍┘?xì)胞需要獲得干細(xì)胞的某些特征例如永生性才能生存和適應(yīng)不斷變化的環(huán)境。永生能力使得細(xì)胞能夠不斷自我更新，并能生成可分化為其他細(xì)胞類型的祖細(xì)胞，”Wahl說(shuō)：“所有的腫瘤都是由癌細(xì)胞組成的不同的細(xì)胞聚集物，然而目前我們尚無(wú)法了解腫瘤異質(zhì)性形成的機(jī)制。”
　　過(guò)去科學(xué)家們將腫瘤的細(xì)胞多樣性主要?dú)w因于其具有遺傳不穩(wěn)定性。隨著腫瘤細(xì)胞群擴(kuò)增，個(gè)別細(xì)胞發(fā)生隨機(jī)突變，細(xì)胞的分子特性開(kāi)始出現(xiàn)差異，最終由成百萬(wàn)的各不相同的癌細(xì)胞共同構(gòu)成了腫瘤。此外一些科學(xué)家們還認(rèn)為腫瘤的異質(zhì)性是由于完全定型和特化的細(xì)胞在腫瘤發(fā)生和發(fā)展的過(guò)程中發(fā)生了去分化所造成的。然而最終這一理論被丟棄，取而代之的當(dāng)前流行的癌干細(xì)胞理論。癌干細(xì)胞理論認(rèn)為腫瘤中存在一類重要的細(xì)胞即癌干細(xì)胞。這些癌干細(xì)胞有可能起源于正常干細(xì)胞或早期祖細(xì)胞，與其他腫瘤細(xì)胞不同它們具有自我更新的能力并可像正常干細(xì)胞一樣生成非干細(xì)胞?！拔覀兊难芯拷Y(jié)果表明與干細(xì)胞相似的癌細(xì)胞并不是早期腫瘤的組成部分，而是在腫瘤發(fā)生的后期隨著p53功能的喪失才出現(xiàn)的，“論文的共同作者、博士后研究人員Benjamin T. Spike說(shuō)：“腫瘤異質(zhì)性有可能是由于不斷增長(zhǎng)的基因組不穩(wěn)定性和與干細(xì)胞樣表型相關(guān)的表觀遺傳不穩(wěn)定性共同作用所致?！?BR>在新研究中研究人員證實(shí)p53不止發(fā)揮了“基因組衛(wèi)士”的功能，這個(gè)腫瘤抑制因子同時(shí)還是阻斷體細(xì)胞重編程的一個(gè)重要障礙。
　　為了確定p53失活對(duì)于干細(xì)胞樣癌細(xì)胞出現(xiàn)的影響，Spike和Mizuno對(duì)乳腺癌和肺癌中的幾百個(gè)基因表達(dá)圖譜進(jìn)行了嚴(yán)密地篩查，尋找干細(xì)胞樣的標(biāo)記，檢測(cè)它們與p53狀態(tài)的聯(lián)系?！拔覀儼l(fā)現(xiàn)p53突變或失活的腫瘤與干細(xì)胞在基因表達(dá)模式上有著密切的聯(lián)系，”Spike說(shuō)：“p53喪失使得細(xì)胞克服了死亡和增殖障礙從而產(chǎn)生了致瘤性。”Wahl希望在接下來(lái)的研究中能夠更深入地了解腫瘤細(xì)胞向干細(xì)胞樣狀態(tài)轉(zhuǎn)化的過(guò)程?！澳[瘤越接近干細(xì)胞狀態(tài)就越具有侵襲性，但是它們?nèi)匀痪哂蟹只癁檩^低侵襲性的細(xì)胞類型的能力，”Wahlshuo ：“如果我們能夠利用這一潛力，我們或許就能迫使這些細(xì)胞重新分化，從而降低它們的危險(xiǎn)性。 ”

【點(diǎn)評(píng)】
　　該研究表明干細(xì)胞樣癌細(xì)胞不是腫瘤起因，而是結(jié)果，p53在腫瘤發(fā)生后期可以阻止腫瘤細(xì)胞向干細(xì)胞樣狀態(tài)轉(zhuǎn)化，從而降低其侵襲性。

【原文摘錄】PNAS  DOI: 10.1073/pnas.1017001108
Inactivation of p53 in breast cancers correlates with stem cell transcriptional signatures
Hideaki Mizuno, Benjamin T. Spikec, Geoffrey M. Wahlc, and Arnold J. Levine
Breast cancer comprises a heterogeneous set of diseases distinguishable from one another by pathologic presentation and molecular signatures. However, each breast cancer subtype is also heterogeneous. Some of the heterogeneity may be attributable to genetic instability, but recent data emphasize that developmental plasticity may also contribute. The p53 tumor suppressor could constitute a nodal control point underlying both sources of heterogeneity because it is frequently inactivated during malignant progression and has recently been shown to function as a potent barrier preventing fully differentiated cells from reverting to pluripotent stem cells after expression of appropriate oncogenes. Using archival microarray datasets, we tested the hypothesis that a p53 mutation could allow cells within a tumor to acquire a stem cell-like state by looking for coordinate expression of stem cell identity genes. We show that breast and lung cancers with p53 mutations do exhibit stem cell-like transcriptional patterns. Such tumors were also depleted for differentiation genes regulated by the polycomb repressor complex 2. These data are consistent with a model in which loss of p53 function enables acquisition of stem cell properties, which are positively selected during tumor progression.

6. 果蠅生殖干細(xì)胞分化新機(jī)制
【摘要】
　　干細(xì)胞是生物體內(nèi)少數(shù)處于無(wú)限增殖，未分化或低分化狀態(tài)并具有多種或一種分化潛能的細(xì)胞群。干細(xì)胞的獨(dú)特能力表現(xiàn)在于，通過(guò)不對(duì)稱分裂產(chǎn)生具有不同命運(yùn)的兩個(gè)子代細(xì)胞，一個(gè)是通過(guò)自我更新，重新產(chǎn)生維持干細(xì)胞特性的新干細(xì)胞；而另一個(gè)子細(xì)胞則步入分化程序，進(jìn)而形成新的組織，或替代生物體中損傷或丟失的組織和器官以維持生命活動(dòng)的延續(xù)。而生殖干細(xì)胞如何維持其未分化狀態(tài)是這一領(lǐng)域的一項(xiàng)核心課題。之前的研究顯示，骨形成蛋白（BMP）對(duì)于維持果蠅生殖干細(xì)胞的未分化狀態(tài)具有重要的意義，這種作用因子可以通過(guò)分化因子Bam，抑制生殖干細(xì)胞的分化，但是這一具體的過(guò)程，至今科學(xué)家們還不是很清楚。
　　來(lái)自中科院動(dòng)物研究所，清華大學(xué)生科院的研究人員發(fā)現(xiàn)了果蠅生殖干細(xì)胞分化的一種新機(jī)制，并且這一機(jī)制也可以延伸到斑馬魚和人類細(xì)胞，這對(duì)于分析生殖干細(xì)胞分化機(jī)制具有重要的意義。這一研究成果公布在上周的Cell雜志上。在這篇文章中，研究人員發(fā)現(xiàn)一種絲氨酸/蘇氨酸激酶：Fused (Fu)能調(diào)控Hedgehog，并與Smurf形成復(fù)合物，通過(guò)BMP應(yīng)答系統(tǒng)操縱果蠅生殖干細(xì)胞的命運(yùn)，而且研究人員在斑馬魚，以及人類細(xì)胞中也發(fā)現(xiàn)了相似的作用，這說(shuō)明這一新機(jī)制可能具有廣泛的保守性。去年陳大華研究組還發(fā)現(xiàn)了泛素介導(dǎo)的細(xì)胞周期蛋白在調(diào)控干細(xì)胞命運(yùn)方面的重要作用，他們以果蠅生殖干細(xì)胞為研究對(duì)象，發(fā)現(xiàn)泛素化過(guò)程相關(guān)的一種重要的基因effete——編碼一種泛素接合酶E2（Ubiquitin-conjugating Enzyme），在調(diào)控果蠅卵巢生殖干細(xì)胞的命運(yùn)決定中發(fā)揮重要作用。
　　進(jìn)一步運(yùn)用遺傳學(xué)、生化及分子生物學(xué)等多種手段研究發(fā)現(xiàn)，Eff蛋白通過(guò)結(jié)合有絲分裂后期促進(jìn)因子APC（一種多亞基的泛素連接酶E3）復(fù)合體中的dAPC2，介導(dǎo)細(xì)胞周期蛋白——Cyclin A的泛素化，從而通過(guò)調(diào)控Cyclin A蛋白水平的變化來(lái)影響生殖干細(xì)胞的命運(yùn)。這將泛素化信號(hào)通路調(diào)控與干細(xì)胞的命運(yùn)決定聯(lián)系起來(lái)，同時(shí)也表明了細(xì)胞周期調(diào)控因子直接控制干細(xì)胞的維持與分化。泛素化機(jī)理和細(xì)胞周期調(diào)控機(jī)制從酵母到高等哺乳動(dòng)物高度保守，說(shuō)明哺乳動(dòng)物中可能存在相似的調(diào)控機(jī)制控制干細(xì)胞的命運(yùn)。

【點(diǎn)評(píng)】
　　對(duì)于干細(xì)胞增殖與分化調(diào)控機(jī)制的認(rèn)識(shí)又前進(jìn)了一步。

【原文摘錄】Cell  doi:10.1016/j.cell.2010.11.022
The Fused/Smurf Complex Controls the Fate of Drosophila Germline Stem Cells by Generating a Gradient BMP Response
Laixin Xia, Shunji Jia, Shoujun Huang, et al.
Highlights
CB differentiation involves antagonism of BMP signaling through regulation of Tkv Fu regulates CB differentiation by antagonizing BMP signal via interaction with Tkv Fu acts in concert with Smurf to terminate BMP signal by ubiquitinating Tkv in CBs Fu has a conserved role in antagonizing BMP/TGFβ signals from fly to vertebrate.
Summary
In the Drosophila ovary, germline stem cells (GSCs) are maintained primarily by bone morphogenetic protein (BMP) ligands produced by the stromal cells of the niche. This signaling represses GSC differentiation by blocking the transcription of the differentiation factor Bam. Remarkably, bam transcription begins only one cell diameter away from the GSC in the daughter cystoblasts (CBs). How this steep gradient of response to BMP signaling is formed has been unclear. Here, we show that Fused (Fu), a serine/threonine kinase that regulates Hedgehog, functions in concert with the E3 ligase Smurf to regulate ubiquitination and proteolysis of the BMP receptor Thickveins in CBs. This regulation generates a steep gradient of BMP activity between GSCs and CBs, allowing for bam expression on CBs and concomitant differentiation. We observed similar roles for Fu during embryonic development in zebrafish and in human cell culture, implying broad conservation of this mechanism.