Cloning and Stem Cells：人兽杂合胚胎不具备干细胞多能性

来自北卡罗来那州维克森林大学(Wake Forest University)医学院，再生医学研究院，德州理工大学，先进细胞技术公司等处的研究人员发现虽然克隆人类胚胎能表达实现多能性需要的各种基因，但是动物-人类的杂合细胞却不具有多能性，这对于从治疗性克隆中分离人类胚胎干细胞意义重大，也是继黄禹锡的造假克隆实验之后的一项重大研究成果。这一研究成果公布在Cloning and Stem Cells杂志上。

领导这一研究的是先进细胞技术公司ACT的研究总监Robert Lanza，他表示，“这些卵细胞不能被重新编程”，人类-动物杂合胚胎无法进行多能性分化。

由于人类卵细胞的缺乏，许多研究人员希望能通过将人类细胞核注射到动物卵细胞中，获得病人特异性的人类胚胎干细胞，虽然这项工作目前并没有得到美国政府的资助，但是在世界各地的许多实验室中都开展了相关内容的研究，其中也包括允许进行动物-人类杂合胚胎研究的英国科学家。

Lanza博士和他的同事分析了体外培养的人-人克隆，人-牛克隆，人-大鼠克隆(主要手段为核移植技术)的早期胚胎的全基因组表达情况，结果他们发现虽然种间杂合的胚胎看起来和人类胚胎相似，但是它们并不具有相同的表达模式。

在人类-动物杂合胚胎中，有大约2300多个基因差异表达，其中大部分是负调控基因，而且引起科学家注意的是，只有人类胚胎能增加关键全能性基因： Oct-4, Sox-2和nanog的表达，“这些细胞不会开启正常的基因，相反，它们会将这些基因关闭或沉默”，Lanza表示。

Lanza的这一研究成果除了否定了杂合胚胎，也为人类治疗性克隆能获得定制的胚胎干细胞提供了新的证据，“这是第一次，不仅发现了细胞重新编程需要的关键的基因，而且捐献DNA重新编程途径与正常胚胎相同。”

而在08年发表在同一杂志上的，来自中国上海交通大学的盛辉(Hui Sheng，音译)等人的研究成果则与之不同，盛辉等人发现在人-牛杂合胚胎晚期，有5个多能性相关基因活跃，其中包括Lanza研究组中分析的3个。 Lanza则对于中国的这一研究结果不以为然，对Sheng的研究组的研究成果表示怀疑。

Cloning and Stem Cells. ahead of print. doi:10.1089/clo.2009.0004.

Reprogramming of Human Somatic Cells Using Human and Animal Oocytes

Young Chung, Colin E. Bishop, Nathan R. Treff, Stephen J. Walker, Vladislav M. Sandler, Sandy Becker, Irina Klimanskaya, Wan-Song Wun, Randall Dunn, Rebecca M. Hall, Jing Su, Shi-Jiang Lu, Marc Maserati, Young-Ho Choi, Richard Scott, Anthony Atala, Ralph Dittman, Robert Lanza.

There is renewed interest in using animal oocytes to reprogram human somatic cells. Here we compare the reprogramming of human somatic nuclei using oocytes obtained from animal and human sources. Comparative analysis of gene expression in morula-stage embryos was carried out using single-embryo transcriptome amplification and global gene expression analyses. Genomic DNA fingerprinting and PCR analysis confirmed that the nuclear genome of the cloned embryos originated from the donor somatic cell. Although the human–human, human–bovine, and human–rabbit clones appeared morphologically similar and continued development to the morula stage at approximately the same rate (39, 36, and 36%, respectively), the pattern of reprogramming of the donor genome was dramatically different. In contrast to the interspecies clones, gene expression profiles of the human–human embryos showed that there was extensive reprogramming of the donor nuclei through extensive upregulation, and that the expression pattern was similar in key upregulation in normal control embryos. To account for maternal gene expression, enucleated oocyte transcriptome profiles were subtracted from the corresponding morula-stage embryo profiles. t-Test comparisons (median-normalized data @ fc > 4; p < 0.005) between human in vitro fertilization (IVF) embryos and human–bovine or human–rabbit interspecies somatic cell transfer (iSCNT) embryos found between 2400 and 2950 genes that were differentially expressed, the majority (60–70%) of which were downregulated, whereas the same comparison between the bovine and rabbit oocyte profiles found no differences at all. In contrast to the iSCNT embryos, expression profiles of human–human clones compared to the age-matched IVF embryos showed that nearly all of the differentially expressed genes were upregulated in the clones. Importantly, the human oocytes significantly upregulated Oct-4, Sox-2, and nanog (22-fold, 6-fold, and 12-fold, respectively), whereas the bovine and rabbit oocytes either showed no difference or a downregulation of these critical pluripotency-associated genes, effectively silencing them. Without appropriate reprogramming, these data call into question the potential use of these discordant animal oocyte sources to generate patient-specific stem cells.