Generation of germline-competent induced pluripotent stem cells

We have previously shown that pluripotent stem cells can be induced from mouse fibroblasts by retroviral introduction of Oct3/4 (also called Pou5f1), Sox2, c-Myc and Klf4, and subsequent selection for Fbx15 (also called Fbxo15) expression. These induced pluripotent stem (iPS) cells (hereafter called Fbx15 iPS cells) are similar to embryonic stem (ES) cells in morphology, proliferation and teratoma formation; however, they are different with regards to gene expression and DNA methylation patterns, and fail to produce adult chimaeras. Here we show that selection for Nanog expression results in germline-competent iPS cells with increased ES-cell-like gene expression and DNA methylation patterns compared with Fbx15 iPS cells. The four transgenes (Oct3/4, Sox2, c-myc and Klf4) were strongly silenced in Nanog iPS cells. We obtained adult chimaeras from seven Nanog iPS cell clones, with one clone being transmitted through the germ line to the next generation. Approximately 20% of the offspring developed tumours attributable to reactivation of the c-myc transgene. Thus, iPS cells competent for germline chimaeras can be obtained from fibroblasts, but retroviral introduction of c-Myc should be avoided for clinical application.     

RNA对基因表达调控作用的研究进展

RNA可以单独或者通过与其它蛋白因子的相互作用参与基因表达的调控。在转录前水平,RNA分子可以通过介导DNA的甲基化或异染色质的形成来调控基因表达;在转录水平,RNA分子通过直接与转录因子或RNA聚合酶相互作用来调控基因表达;在转录后水平,RNA利用由siRNA和microRNA介导的RNA干扰机制,通过降解目标mRNA或阻碍目标基因的翻译来沉默基因的表达。此外,mRNA还可以通过感知环境中代谢物的浓度,通过形成核糖开关（riboswitch）来调控基因的表达;反义RNA可以从复制、转录和翻译3个水平上调控基因的表达。     

Epigenetic inheritance in plants

The function of plant genomes depends on chromatin marks such as the methylation of DNA and the post-translational modification of histones. Techniques for studying model plants such as Arabidopsis thaliana have enabled researchers to begin to uncover the pathways that establish and maintain chromatin modifications, and genomic studies are allowing the mapping of modifications such as DNA methylation on a genome-wide scale. Small RNAs seem to be important in determining the distribution of chromatin modifications, and RNA might also underlie the complex epigenetic interactions that occur between homologous sequences. Plants use these epigenetic silencing mechanisms extensively to control development and parent-of-origin imprinted gene expression.     

反义RNA对质粒复制的调控作用

反义RNA的存在最先是在质粒和其它原核附属DNA元件中被证实的.对这些体系深入的研究揭示了原核反义RNA结构和功能的联系,以及正义/反义RNA相互作用的机理.本文着重叙述反义RNA在质粒复制中的作用及其进展.     

A histone H3 methyltransferase controls DNA methylation in Neurospora crassa.

DNA methylation is involved in epigenetic processes such as X-chromosome inactivation, imprinting and silencing of transposons. We have demonstrated previously that dim-2 encodes a DNA methyltransferase that is responsible for all known cytosine methylation in Neurospora crassa. Here we report that another Neurospora gene, dim-5, is required for DNA methylation, as well as for normal growth and full fertility. We mapped dim-5 and identified it by transformation with a candidate gene. The mutant has a nonsense mutation in a SET domain of a gene related to histone methyltransferases that are involved in heterochromatin formation in other organisms. Transformation of a wild-type strain with a segment of dim-5 reactivated a silenced hph gene, apparently by 'quelling' of dim-5. We demonstrate that recombinant DIM-5 protein specifically methylates histone H3 and that replacement of lysine 9 in histone H3 with either a leucine or an arginine phenocopies the dim-5 mutation. We conclude that DNA methylation depends on histone methylation.