对于动物而言，正在发育的一部分胚能表现出形成不同形态的能力，此外已经具有一定形态和机能的细胞也可以在内外条件发生变化的情况下表现出其它不同形态，这种现象称为多能性（pluripotency）。在已分化的鼠类及人类细胞中，能通过转录因子（transcription factor）Oct4、Sox2、Klf4和c-Myc的逆转录转导（retroviral transduction）来实现多能性的诱导。  

       在2008年2月7日出版的《细胞—干细胞》（Cell Stem Cell）上，来自美国的一组科学家发明了一种新技术，使得以上四种转录因子可以通过强力霉素诱导的慢病毒载体（doxycycline-inducible lentiviral vector）表达。利用这些可诱导构造，研究小组从鼠胚胎纤维原细胞（MEF）中得到了诱导多能干细胞（iPS），并且科学家发现，转基因沉默是正常的细胞分化的先决条件。  

       在研究中，科学家分析了小鼠诱导多能干细胞产生过程中，已知的多能标记物激活的时间，结果发现，碱性磷酸酶（alkaline phosphatase AP）首先被激活，接着是阶段性特异胚胎抗原1（stage specific embryonic antigen SSEA1）。而作为完全再分化细胞标志的Nanog和内生Oct4基因的表达则只在整个过程的后期被观察到。更重要的是，病毒逆转录的cDNA需要至少被表达12天，以产生iPS细胞。研究小组表示，他们的结果对于了解表观遗传修饰（epigenetic reprogramming）的某些分子过程很重要。

（《细胞—干细胞》（Cell Stem Cell），Vol 2, 151-159, 07 February 2008，Tobias Brambrink, Rudolf Jaenisch）

原始出处：

Cell Stem Cell, Vol 2, 151-159, 07 February 2008

Article

Sequential Expression of Pluripotency Markers during Direct Reprogramming of Mouse Somatic Cells

Tobias Brambrink,1,3 Ruth Foreman,1,2,3 G. Grant Welstead,1,3 Christopher J. Lengner,1 Marius Wernig,1 Heikyung Suh,1 and Rudolf Jaenisch1,2,

1 Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, 9 Cambridge Center, Cambridge, MA 02142, USA
2 Department of Biology, Massachusetts Institute of Technology, 31 Ames Street, Cambridge, MA 02139, USA

Corresponding author
Rudolf Jaenisch
jaenisch@wi.mit.edu

Pluripotency can be induced in differentiated murine and human cells by retroviral transduction of Oct4, Sox2, Klf4, and c-Myc. We have devised a reprogramming strategy in which these four transcription factors are expressed from doxycycline (dox)-inducible lentiviral vectors. Using these inducible constructs, we derived induced pluripotent stem (iPS) cells from mouse embryonic fibroblasts (MEFs) and found that transgene silencing is a prerequisite for normal cell differentiation. We have analyzed the timing of known pluripotency marker activation during mouse iPS cell derivation and observed that alkaline phosphatase (AP) was activated first, followed by stage-specific embryonic antigen 1 (SSEA1). Expression of Nanog and the endogenous Oct4 gene, marking fully reprogrammed cells, was only observed late in the process. Importantly, the virally transduced cDNAs needed to be expressed for at least 12 days in order to generate iPS cells. Our results are a step toward understanding some of the molecular events governing epigenetic reprogramming.