细胞命运转变——谱系重编程技术研究进展

体细胞核移植和诱导多能干细胞技术表明已分化的体细胞可以转变命运。最近的研究再一次验证了成熟体细胞可以通过外源转录因子的导入,直接重编程为其他类型的体细胞或祖细胞。这种重编程技术称为谱系重编程(Lineage reprogramming)。这项技术不仅在再生医学领域具有广阔的应用前景,而且在动物生物技术中也应用广泛。它不但避免了伦理争议,还提供了便利的重编程方法,同时也为基因表达调控的研究提供了重要的手段。文章从谱系重编程的方式、谱系重编程的特点及应用前景等3个方面进行了综述,旨在对相关领域的研究人员起到借鉴作用。     

The evolving biology of small molecules: controlling cell fate and identity

Small molecules have been playing important roles in elucidating basic biology and treatment of a vast number of diseases for nearly a century, making their use in the field of stem cell biology a comparatively recent phenomenon. Nonetheless, the power of biology-oriented chemical design and synthesis, coupled with significant advances in screening technology, has enabled the discovery of a growing number of small molecules that have improved our understanding of stem cell biology and allowed us to manipulate stem cells in unprecedented ways. This review focuses on recent small molecule studies of (i) the key pathways governing stem cell homeostasis, (ii) the pluripotent stem cell niche, (iii) the directed differentiation of stem cells, (iv) the biology of adult stem cells, and (v) somatic cell reprogramming. In a very short period of time, small molecules have defined a perhaps universally attainable naive ground state of pluripotency, and are facilitating the precise, rapid and efficient differentiation of stem cells into somatic cell populations relevant to the clinic. Finally, following the publication of numerous groundbreaking studies at a pace and consistency unusual for a young field, we are closer than ever to completely eliminating the need for genetic modification in reprogramming.     

Planarian stem cells specify fate yet retain potency during the cell cycle

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诱导多能干细胞 (iPS) 的诱导培养与鉴定

通过外源转录调控因子的诱导,使成体细胞重编程为胚胎干细胞(ES细胞)样的多能细胞,这种细胞称为诱导多能干细胞(iPS细胞),这一方法被称为iPS技术。目前,iPS技术已先后在小鼠、人、猕猴、大鼠和猪中成功应用,建立了相应的iPS细胞系,并获得了iPS细胞嵌合小鼠和四倍体克隆小鼠。尽管iPS与ES细胞在形态和生长特性上有许多相同之处,但iPS细胞的建立需要较独特的诱导培养体系和鉴定方法。以下结合近年来iPS技术的发展和本实验室的相关研究,对iPS细胞的建立和培养体系的优化进行了深入探讨。     

Regulatory genes controlling cell fate choice in embryonic and adult neural stem cells

Neural stem cells are the most immature progenitor cells in the nervous system and are defined by their ability to self-renew by symmetric division as well as to give rise to more mature progenitors of all neural lineages by asymmetric division (multipotentiality). The interest in neural stem cells has been growing in the past few years following the demonstration of their presence also in the adult nervous system of several mammals, including humans. This observation implies that the brain, once thought to be entirely post-mitotic, must have at least a limited capacity for self-renewal. This raises the possibility that the adult nervous system may still have the necessary plasticity to undergo repair of inborn defects and acquired injuries, if ways can be found to exploit the potential of neural stem cells (either endogenous or derived from other sources) to replace damaged or defective cells. A full understanding of the molecular mechanisms regulating generation and maintenance of neural stem cells, their choice between different differentiation programmes and their migration properties is essential if these cells are to be used for therapeutic applications. Here, we summarize what is currently known of the genes and the signalling pathways involved in these mechanisms.     

Dysfunctional mitochondrial fission impairs cell reprogramming

We have recently shown that mitochondrial fission is induced early in reprogramming in a Drp1-dependent manner; however, the identity of the factors controlling Drp1 recruitment to mitochondria was unexplored. To investigate this, we used a panel of RNAi targeting factors involved in the regulation of mitochondrial dynamics and we observed that MiD51, Gdap1 and, to a lesser extent, Mff were found to play key roles in this process. Cells derived from Gdap1-null mice were used to further explore the role of this factor in cell reprogramming. Microarray data revealed a prominent down-regulation of cell cycle pathways in Gdap1-null cells early in reprogramming and cell cycle profiling uncovered a G2/M growth arrest in Gdap1-null cells undergoing reprogramming. High-Content analysis showed that this growth arrest was DNA damage-independent. We propose that lack of efficient mitochondrial fission impairs cell reprogramming by interfering with cell cycle progression in a DNA damage-independent manner.     

Identification of a fat cell enhancer: analysis of requirements for adipose tissue-specific gene expression.

The molecular basis for adipose-specific gene expression is not known. To approach the problem of adipocyte gene expression, we have analyzed in detail the capacity of the 5'-flanking region of the adipocyte P2 (aP2) gene to direct cell-type specific gene expression. Although the proximal promoter containing AP-1 and C/EBP binding sites is capable of directing differentiation-dependent gene expression in cultured adipocytes, these constructs are essentially inactive in the tissues of transgenic mice. We found that -5.4 kb of the 5'-flanking region were required to direct heterologous gene (chloramphenicol acetyl transferase; CAT) expression to the adipose tissue of transgenic mice. By deletion analysis, we identified a 520 bp enhancer at -5.4 kb of the aP2 gene. We show that this enhancer can direct high levels of gene expression specifically to the adipose tissue of transgenic mice. This enhancer also functions in a differentiation-dependent manner in cultured adipocytes and cannot be transactivated in preadipocytes by C/EBP. Molecular analysis indicates that several cis- and trans- acting acting elements, though not C/EBP, contribute to the specificity and potency of this enhancer.     

细胞重编程的分子机制

细胞重编程,尤其是诱导多能性干细胞的出现,给再生医学带来极大的希望。近年来,这方面的研究吸引了众多科学家的参与,也取得了非常丰富的成果。本文主要从转录因子、表观遗传和信号转导等角度,介绍了细胞重编程分子机制研究方面的进展和未来的方向。     

C/EBPα在非小细胞肺癌中的表达及其与微血管密度的关系

目的:探讨C/EBPα在非小细胞肺癌(non-small cell lung cancer,NSCLC)组织中的表达及其与肿瘤微血管密度(microvessel density,MVD)的关系.方法:应用免疫组织化学EnVision法检测40例手术切除的NSCLC组织及其配对的40例距肿瘤＞5 cm以上癌旁正常肺组织中C/EBPα蛋白的表达,并分析C/EBPα在NSCLC中的表达与其临床病理特征的关系.采用CD34标记肺癌组织中的肿瘤微血管,分析C/EBPα的表达与肿瘤MVD的关系.结果:NSCLC组织中C/EBPα的阳性表达率明显低于癌旁正常肺组织(P＜0.05).C/EBPα与NSCLC患者的年龄、性别、TNM分期及有无淋巴结转移均无关(P＞0.05),与NSCLC组织的分化程度及病理类型有关(P＜0.05).在NSCLC组织中,C/EBPα蛋白表达阳性组MVD明显低于C/EBPα蛋白表达阴性组(P＜0.05).结论:C/EBPα在NSCLC中的低表达可能通过调节MVD介导NSCLC的发生和发展.