Concept: Somatic cell nuclear transfer
Somatic cell nuclear transfer (SCNT) is a unique technology that produces cloned animals from single cells. It is desirable from a practical viewpoint that donor cells can be collected noninvasively and used readily for nuclear transfer. The present study was undertaken to determine whether peripheral blood cells freshly collected from living mice could be used for SCNT. We collected a drop of peripheral blood (15-45 µl) from the tail of a donor. A nucleated cell (leukocyte) suspension was prepared by lysing the red blood cells. Following SCNT using randomly selected leukocyte nuclei, cloned offspring were born at a 2.8% birth rate. Fluorescence-activated cell sorting revealed that granulocytes/monocytes and lymphocytes could be roughly distinguished by their sizes, the former being significantly larger. We then cloned putative granulocytes/monocytes and lymphocytes separately, and obtained 2.1% and 1.7% birth rates, respectively (P > 0.05). Because the use of lymphocyte nuclei inevitably results in the birth of offspring with DNA rearrangements, we applied granulocyte/monocyte cloning to two genetically modified strains and two recombinant inbred strains. Normal-looking offspring were obtained from all four strains tested. The present study clearly indicated that genetic copies of mice could be produced using a drop of peripheral blood from living donors. This strategy will be applied to the rescue of infertile founder animals or a “last-of-line” animal possessing invaluable genetic resources.
Myostatin (MSTN) has been shown to be a negative regulator of skeletal muscle development and growth. MSTN dysfunction therefore offers a strategy for promoting animal growth performance in livestock production. In this study, we investigated the possibility of using RNAi-based technology to generate transgenic sheep with a double-muscle phenotype. A shRNA expression cassette targeting sheep MSTN was used to generate stable shRNA-expressing fibroblast clones. Transgenic sheep were further produced by somatic cell nuclear transfer (SCNT) technology. Five lambs developed to term and three live lambs were obtained. Integration of shRNA expression cassette in three live lambs was confirmed by PCR. RNase protection assay showed that the shRNAs targeting MSTN were expressed in muscle tissues of three transgenic sheep. MSTN expression was significantly inhibited in muscle tissues of transgenic sheep when compared with control sheep. Moreover, transgenic sheep showed a tendency to faster increase in body weight than control sheep. Histological analysis showed that myofiber diameter of transgenic sheep M17 were bigger than that of control sheep. Our findings demonstrate a promising approach to promoting muscle growth in livestock production.
Reprogramming somatic cells into pluripotent embryonic stem cells (ESCs) by somatic cell nuclear transfer (SCNT) has been envisioned as an approach for generating patient-matched nuclear transfer (NT)-ESCs for studies of disease mechanisms and for developing specific therapies. Past attempts to produce human NT-ESCs have failed secondary to early embryonic arrest of SCNT embryos. Here, we identified premature exit from meiosis in human oocytes and suboptimal activation as key factors that are responsible for these outcomes. Optimized SCNT approaches designed to circumvent these limitations allowed derivation of human NT-ESCs. When applied to premium quality human oocytes, NT-ESC lines were derived from as few as two oocytes. NT-ESCs displayed normal diploid karyotypes and inherited their nuclear genome exclusively from parental somatic cells. Gene expression and differentiation profiles in human NT-ESCs were similar to embryo-derived ESCs, suggesting efficient reprogramming of somatic cells to a pluripotent state.
Derivation of patient-specific human pluripotent stem cells via somatic cell nuclear transfer (SCNT) has the potential for applications in a range of therapeutic contexts. However, successful SCNT with human cells has proved challenging to achieve, and thus far has only been reported with fetal or infant somatic cells. In this study, we describe the application of a recently developed methodology for the generation of human ESCs via SCNT using dermal fibroblasts from 35- and 75-year-old males. Our study therefore demonstrates the applicability of SCNT for adult human cells and supports further investigation of SCNT as a strategy for regenerative medicine.
Previous studies of serial cloning in animals showed a decrease in efficiency over repeated iterations and a failure in all species after a few generations. This limitation led to the suggestion that repeated recloning might be inherently impossible because of the accumulation of lethal genetic or epigenetic abnormalities. However, we have now succeeded in carrying out repeated recloning in the mouse through a somatic cell nuclear transfer method that includes a histone deacetylase inhibitor. The cloning efficiency did not decrease over 25 generations, and, to date, we have obtained more than 500 viable offspring from a single original donor mouse. The reprogramming efficiency also did not increase over repeated rounds of nuclear transfer, and we did not see the accumulation of reprogramming errors or clone-specific abnormalities. Therefore, our results show that repeated iterative recloning is possible and suggest that, with adequately efficient techniques, it may be possible to reclone animals indefinitely.
Cloned embryonic stem cells (ESCs) are the tools used for therapeutic cloning, which is designed to remedy disease, not as a means for reproduction. Thirteen years after the first successful derivation of cloned ESCs in mice, and eleven years after the first application of therapeutic cloning also in mice, these pluripotent cells have now been produced in humans. The work of Tachibana and colleagues (Cell, May 2013) shows that the cytoplasm of the human oocyte, like that of several other mammalian species, is endowed with reprogramming capacity after somatic cell nuclear transfer (SCNT). The developmental rates, up to 60% for blastocyst formation and up to 50% for ESC derivation, are very competitive in comparison with the alternative technology of the induced pluripotent stem cells (iPSCs). What did Tachibana and colleagues do differently from the other investigators whose previous attempts to produce cloned human blastocysts and ESCs were unsuccessful? The authors developed a highly refined method for oocyte enucleation and embryo culture, and meticolously selected the oocytes. What does the achievement of the cloned human ESCs mean for basic science and for biomedicine? The reprogramming factors of the human oocyte can be mined and transferred to other reprogramming systems, such as iPSC. Human iPSC’s reprogramming can now be tested against a natural reference-the human oocyte. The achievement of Tachibana and colleagues is a great leap forward for knowledge. It also raises questions, for instance the extent of potency of cloned human embryos, and some issues that society will likely have to confront, such as the principles that should guide the allocation of human oocytes for reproductive versus non-reproductive purposes.
Recently in Cell, Mitalipov and colleagues report an advance that has eluded scientists for over a decade-the successful derivation of embryonic stem cell lines using somatic cell nuclear transfer, or SCNT (Tachibana et al., 2013).
- Proceedings of the National Academy of Sciences of the United States of America
- Published over 4 years ago
Cellular reprogramming is a new and rapidly emerging field in which somatic cells can be turned into pluripotent stem cells or other somatic cell types simply by the expression of specific combinations of genes. By viral expression of neural fate determinants, it is possible to directly reprogram mouse and human fibroblasts into functional neurons, also known as induced neurons. The resulting cells are nonproliferating and present an alternative to induced pluripotent stem cells for obtaining patient- and disease-specific neurons to be used for disease modeling and for development of cell therapy. In addition, because the cells do not pass a stem cell intermediate, direct neural conversion has the potential to be performed in vivo. In this study, we show that transplanted human fibroblasts and human astrocytes, which are engineered to express inducible forms of neural reprogramming genes, convert into neurons when reprogramming genes are activated after transplantation. Using a transgenic mouse model to specifically direct expression of reprogramming genes to parenchymal astrocytes residing in the striatum, we also show that endogenous mouse astrocytes can be directly converted into neural nuclei (NeuN)-expressing neurons in situ. Taken together, our data provide proof of principle that direct neural conversion can take place in the adult rodent brain when using transplanted human cells or endogenous mouse cells as a starting cell for neural conversion.
Human pluripotent stem cells hold potential for regenerative medicine, but available cell types have significant limitations. Although embryonic stem cells (ES cells) from in vitro fertilized embryos (IVF ES cells) represent the ‘gold standard’, they are allogeneic to patients. Autologous induced pluripotent stem cells (iPS cells) are prone to epigenetic and transcriptional aberrations. To determine whether such abnormalities are intrinsic to somatic cell reprogramming or secondary to the reprogramming method, genetically matched sets of human IVF ES cells, iPS cells and nuclear transfer ES cells (NT ES cells) derived by somatic cell nuclear transfer (SCNT) were subjected to genome-wide analyses. Both NT ES cells and iPS cells derived from the same somatic cells contained comparable numbers of de novo copy number variations. In contrast, DNA methylation and transcriptome profiles of NT ES cells corresponded closely to those of IVF ES cells, whereas iPS cells differed and retained residual DNA methylation patterns typical of parental somatic cells. Thus, human somatic cells can be faithfully reprogrammed to pluripotency by SCNT and are therefore ideal for cell replacement therapies.
It is well known that both recipient cells and donor nuclei demonstrate a mitotic advantage as observed in the traditional reprogramming with somatic cell nuclear transfer (SCNT). However, it is not known whether a specific mitotic factor plays a critical role in reprogramming. Here we identify an isoform of human bromodomain-containing 3 (BRD3), BRD3R (BRD3 with Reprogramming activity), as a reprogramming factor. BRD3R positively regulates mitosis during reprogramming, upregulates a large set of mitotic genes at early stages of reprogramming, and associates with mitotic chromatin. Interestingly, a set of the mitotic genes upregulated by BRD3R constitutes a pluripotent molecular signature. The two BRD3 isoforms display differential binding to acetylated histones. Our results suggest a molecular interpretation for the mitotic advantage in reprogramming and show that mitosis may be a driving force of reprogramming.