Induced pluripotent stem cell lines derived from human somatic cells

Somatic cell nuclear transfer allows trans-acting factors present in the mammalian oocyte to reprogram somatic cell nuclei to an undifferentiated state. We show that four factors (OCT4, SOX2, NANOG, and LIN28) are sufficient to reprogram human somatic cells to pluripotent stem cells that exhibit the essential characteristics of embryonic stem (ES) cells. These induced pluripotent human stem cells have normal karyotypes, express telomerase activity, express cell surface markers and genes that characterize human ES cells, and maintain the developmental potential to differentiate into advanced derivatives of all three primary germ layers. Such induced pluripotent human cell lines should be useful in the production of new disease models and in drug development, as well as for applications in transplantation medicine, once technical limitations (for example, mutation through viral integration) are eliminated.     

人端粒酶活性的调控机制及其新功能研究进展

端粒酶活性在胚胎发育过程中消失,人的绝大多数体细胞没有端粒酶活性,因而随着体细胞分裂次数的增加,端粒长度在不断缩短.当端粒缩短到一定程度时,细胞无法维持正常的端粒结构而导致细胞的衰老,而当细胞衰老调控机制失控的情况下,端粒的极限缩短将导致细胞死亡或癌变.端粒酶的活性在细胞癌变的过程中被重新激活以维持端粒的长度和结构,以及细胞无限增殖化的能力,与衰老及肿瘤的发生发展密.切相关.随着人们对端粒酶认识的深入,新研究进展显示端粒酶具有独立于端粒之外的新功能,端粒酶在DNA修复、促进细胞存活、基因转录及刺激干细胞增殖等方面不依赖于端粒的新功能的发现,为阐明端粒酶在衰老及癌变中重要功能的分子机制提供了新的思路.     

人类胚胎干细胞研究述评

对人类胚胎干细胞(hESCs)的来源、培养方法、建系条件、生物学特性和鉴定方法、遗传操作及其需解决的问题进行了讨论。提出目前研究的重点在于揭示维持ES细胞多能性和自我更新的机理,进一步优化人类和其他哺乳动物类ES细胞的分离、培养、建系方法,探讨其定向分化机理,建立胚胎干细胞(ESCs)和胚胎生殖细胞(EGCs)的大规模快速扩增技术;完善hESCs向重要功能细胞(生殖细胞)分化的体系;单细胞比对分析ESCs、畸胎瘤细胞(ECSs)、EGCs、类胚体(EBs)、各级生殖细胞和成体细胞的基因及蛋白表达图谱,以探求生殖细胞、成体细胞、ESCs、ECSs、EGCs的本质区别,积极开展将ES细胞用于治疗人类疾病模型的研究。     

Penetration of somatic mammalian cells by sperm

Penetration of somatic mammalian cells by spermatozoa occurred after simple admixture in culture. With sperm labeled in vivo, autoradiography revealed incorporation of DNA into nuclei of recipient cells, indicating release of DNA after entrance by sperm. This system provides a new approach to study the molecular biology of information transfer and of haploid gene expression.     

Differentiation of embryonic stem cell lines generated from adult somatic cells by nuclear transfer

Embryonic stem (ES) cells are fully pluripotent in that they can differentiate into all cell types, including gametes. We have derived 35 ES cell lines via nuclear transfer (ntES cell lines) from adult mouse somatic cells of inbred, hybrid, and mutant strains. ntES cells contributed to an extensive variety of cell types, including dopaminergic and serotonergic neurons in vitro and germ cells in vivo. Cloning by transfer of ntES cell nuclei could result in normal development of fertile adults. These studies demonstrate the full pluripotency of ntES cells.     

Embryonic stem cells. Stem cell programs

The availability of human embryonic stem cell lines provides an important tool for scientists to explore the fundamental mechanisms that regulate differentiation into specific cell types. When more is known about the mechanisms that govern these processes, human embryonic stem cells may be clinically useful in generating cell types that have been damaged or depleted by a variety of human diseases. The NIH is actively pursuing a variety of initiatives to promote this developing research field, while continuing and expanding its long-standing investment in adult stem cells and research.     

Generation of mouse induced pluripotent stem cells without viral vectors

Induced pluripotent stem (iPS) cells have been generated from mouse and human somatic cells by introducing Oct3/4 and Sox2 with either Klf4 and c-Myc or Nanog and Lin28 using retroviruses or lentiviruses. Patient-specific iPS cells could be useful in drug discovery and regenerative medicine. However, viral integration into the host genome increases the risk of tumorigenicity. Here, we report the generation of mouse iPS cells without viral vectors. Repeated transfection of two expression plasmids, one containing the complementary DNAs (cDNAs) of Oct3/4, Sox2, and Klf4 and the other containing the c-Myc cDNA, into mouse embryonic fibroblasts resulted in iPS cells without evidence of plasmid integration, which produced teratomas when transplanted into mice and contributed to adult chimeras. The production of virus-free iPS cells, albeit from embryonic fibroblasts, addresses a critical safety concern for potential use of iPS cells in regenerative medicine.     

Progress,problems and prospects of porcine pluripotent stem cells

Pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced PSCs (iPSCs), can differentiate into cells of the three germ layers, suggesting that PSCs have great potential for basic developmental biology research and wide applications for clinical medicine. Genuine ESCs and iPSCs have been derived from mice and rats, but not from livestock such as the pig—an ideal animal model for studying human disease and regenerative medicine due to similarities with human physiologic processes. Efforts to derive porcine ESCs and iPSCs have not yielded high-quality PSCs that can produce chimeras with germline transmission. Thus, exploration of the unique porcine gene regulation network of preimplantation embryonic development may permit optimization of in vitro culture systems for raising porcine PSCs. Here we summarize the recent progress in porcine PSC generation as well as the problems encountered during this progress and we depict prospects for generating porcine naive PSCs.     

Specific mutations induced by triplex-forming oligonucleotides in mice

Triplex-forming oligonucleotides (TFOs) recognize and bind to specific duplex DNA sequences and have been used extensively to modify gene function in cells. Although germ line mutations can be incorporated by means of embryonic stem cell technology, little progress has been made toward introducing mutations in somatic cells of living organisms. Here we demonstrate that TFOs can induce mutations at specific genomic sites in somatic cells of adult mice. Mutation detection was facilitated by the use of transgenic mice bearing chromosomal copies of the supF and cII reporter genes. Mice treated with a supF-targeted TFO displayed about fivefold greater mutation frequencies in the supF gene compared with mice treated with a scrambled sequence control oligomer. No mutagenesis was detected in the control gene (cII) with either oligonucleotide. These results demonstrate that site-specific, TFO-directed genome modification can be accomplished in intact animals.     

Induced pluripotent stem cells generated from patients with ALS can be differentiated into motor neurons

The generation of pluripotent stem cells from an individual patient would enable the large-scale production of the cell types affected by that patient's disease. These cells could in turn be used for disease modeling, drug discovery, and eventually autologous cell replacement therapies. Although recent studies have demonstrated the reprogramming of human fibroblasts to a pluripotent state, it remains unclear whether these induced pluripotent stem (iPS) cells can be produced directly from elderly patients with chronic disease. We have generated iPS cells from an 82-year-old woman diagnosed with a familial form of amyotrophic lateral sclerosis (ALS). These patient-specific iPS cells possess properties of embryonic stem cells and were successfully directed to differentiate into motor neurons, the cell type destroyed in ALS.     

Gene for human insulin receptor: localization to site on chromosome 19 involved in pre-B-cell leukemia

Consistent chromosomal translocations in neoplastic cells may alter the expression of proto-oncogenes that are located near the breakpoints. The complementary DNA sequence of the human insulin receptor is similar to those of the EGF receptor (erbB oncogene) and products of the src family of oncogenes. With in situ hybridization and Southern blot analysis of somatic cell hybrid DNA, the human insulin receptor gene was mapped to the distal short arm of chromosome 19 (bands p13.2----p13.3), a site involved in a nonrandom translocation in pre-B-cell acute leukemia.     

Reactivation of an inactive human X chromosome: evidence for X inactivation by DNA methylation

A mouse-human somatic cell hybrid clone, deficient in hypoxanthine-guanine phosphoribosyltransferase (HPRT) and containing a structurally normal inactive human X chromosome, was isolated. The hybrid cells were treated with 5-azacytidine and tested for the reactivation and expression of human X-linked genes. The frequency of HPRT-positives clones after 5-azacytidine treatment was 1000-fold greater than that observed in untreated hybrid cells. Fourteen independent HPRT-positive clones were isolated and analyzed for the expression of human X markers. Isoelectric focusing showed that the HPRT expressed in these clones is human. One of the 14 clones expressed human glucose-6-phosphate dehydrogenase and another expressed human phosphoglycerate kinase. Since 5-azacytidine treatment results in hypomethylation of DNA, DNA methylation may be a mechanism of human X chromosome inactivation.     

The past,present and future of bovine pluripotent stem cells: a brief overview

Although the pursuit of bovine embryonic stem cells started more than 26 years ago for the purpose of gene-targeting, true pluripotent stem cells in this economically important species are still elusive. With the rapid advances in genome-editing and cloning using homologously recombined somatic cells, the need for pluripotent stem cells for precise genetic modification in any species became questionable. With the pig being the better model for human regenerative biology, the identification of the commonalities and uniqueness of the pluripotency circuitry across mammalian species may be the main objective for studying pluripotent stem cells in the bovine.     

Germ-line transmission of a c-abl mutation produced by targeted gene disruption in ES cells

A substitution mutation has been introduced into the c-abl locus of murine embryonic stem cells by homologous recombination between exogenously added DNA and the endogenous gene, and these cells have been used to generate chimeric mice. It is shown that the c-abl mutation was transmitted to progeny by several male chimeras. This work demonstrates the feasibility of germ-line transmission of a mutation introduced into a nonselectable autosomal gene by homologous recombination.