Fertilization of mammalian eggs is followed by successive cell divisions and progressive differentiation, first into the early embryo and subsequently into all of the cell types that make up the adult animal. Transfer of a single nucleus at a specific stage of development, to an enucleated unfertilized egg, provided an opportunity to investigate whether cellular differentiation to that stage involved irreversible genetic modification. The first offspring to develop from a differentiated cell were born after nuclear transfer from an embryo-derived cell line that had been induced to become quiescent. Using the same procedure, we now report the birth of live lambs from three new cell populations established from adult mammary gland, fetus and embryo. The fact that a lamb was derived from an adult cell confirms that differentiation of that cell did not involve the irreversible modification of genetic material required for development to term. The birth of lambs from differentiated fetal and adult cells also reinforces previous speculation that by inducing donor cells to become quiescent it will be possible to obtain normal development from a wide variety of differentiated cells.

Nuclear transfer has been used in mammals as both a valuable tool in embryological studies and as a method for the multiplication of 'elite' embryos. Offspring have only been reported when early embryos, or embryo-derived cells during primary culture, were used as nuclear donors. Here we provide the first report, to our knowledge, of live mammalian offspring following nuclear transfer from an established cell line. Lambs were born after cells derived from sheep embryos, which had been cultured for 6 to 13 passages, were induced to quiesce by serum starvation before transfer of their nuclei into enucleated oocytes. Induction of quiescence in the donor cells may modify the donor chromatin structure to help nuclear reprogramming and allow development. This approach will provide the same powerful opportunities for analysis and modification of gene function in livestock species that are available in the mouse through the use of embryonic stem cells.

Manipulation or non-physiological embryo culture environments can lead to defective fetal programming in livestock. Our demonstration of reduced fetal methylation and expression of ovine IGF2R suggests pre-implantation embryo procedures may be vulnerable to epigenetic alterations in imprinted genes. This highlights the potential benefits of epigenetic diagnostic screening in developing embryo procedures.

Ovine primary fetal fibroblasts were cotransfected with a neomycin resistance marker gene (neo) and a human coagulation factor IX genomic construct designed for expression of the encoded protein in sheep milk. Two cloned transfectants and a population of neomycin (G418)-resistant cells were used as donors for nuclear transfer to enucleated oocytes. Six transgenic lambs were liveborn: Three produced from cloned cells contained factor IX and neo transgenes, whereas three produced from the uncloned population contained the marker gene only. Somatic cells can therefore be subjected to genetic manipulation in vitro and produce viable animals by nuclear transfer. Production of transgenic sheep by nuclear transfer requires fewer than half the animals needed for pronuclear microinjection.

Glial proliferation and activation are associated with disease progression in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar dementia. In this study, we describe a unique platform to address the question of cell autonomy in transactive response DNAbinding protein (TDP-43) proteinopathies. We generated functional astroglia from human induced pluripotent stem cells carrying an ALScausing TDP-43 mutation and show that mutant astrocytes exhibit increased levels of TDP-43, subcellular mislocalization of TDP-43, and decreased cell survival. We then performed coculture experiments to evaluate the effects of M337V astrocytes on the survival of wild-type and M337V TDP-43 motor neurons, showing that mutant TDP-43 astrocytes do not adversely affect survival of cocultured neurons. These observations reveal a significant and previously unrecognized glial cell-autonomous pathological phenotype associated with a pathogenic mutation in TDP-43 and show that TDP-43 proteinopathies do not display an astrocyte non-cell-autonomous component in cell culture, as previously described for SOD1 ALS. This study highlights the utility of induced pluripotent stem cell-based in vitro disease models to investigate mechanisms of disease in ALS and other TDP-43 proteinopathies.glia | motor neuron disease | disease modeling T ransactive response DNA-binding protein (TDP-43) is the major component of ubiquitinated cytoplasmic and nuclear inclusions in neurons and astroglia in amyotrophic lateral sclerosis (ALS) and a subgroup of frontotemporal lobar degeneration (FTLD-TDP) (1-3). These pathological hallmarks provide a unifying description of a range of conditions defined as TDP-43 proteinopathies (4). At present, >30 mutations in the TDP-43 gene (TARDBP) have been linked to familial ALS (fALS) (5), strongly suggesting a causative role for TDP-43 in the pathogenesis of ALS.Accumulating evidence from experimental systems implicating non-cell-autonomous mechanisms in ALS has highlighted the importance of the glial cellular environment to motor neuron (MN) degeneration (1,3,(6)(7)(8)(9). In vivo rodent models of ALS with lineage-specific SOD1 expression have particularly influenced our understanding of the nonneuronal contribution to disease progression. Glial expression of mutant SOD1 cannot initiate MN disease on its own, but is necessary for disease progression (6, 7). Furthermore, astrogliosis precedes MN degeneration in some animal models and is a dominant feature of all human ALS pathology (4, 6, 10). Collectively, these observations highlight the need to better understand the nature of astroglial pathology in ALS. Combining developmental neurobiological principles of cell fate determination with human induced pluripotent stem cell (iPSC) lines derived from patients carrying ALS disease-causing mutations may provide important insights into astroglia pathology.We recently generated human MNs from iPSC lines derived from a fALS patient and demonstrated that the M337V TDP-43 mutation confers cell-autonomous toxicity to MNs (11). More...

Transactive response protein is the dominant disease protein in amyotrophic lateral sclerosis (ALS) and a subgroup of frontotemporal lobar degeneration (FTLD-TDP). Identification of mutations in the gene encoding TDP-43 (TARDBP) in familial ALS confirms a mechanistic link between misaccumulation of TDP-43 and neurodegeneration and provides an opportunity to study TDP-43 proteinopathies in human neurons generated from patient fibroblasts by using induced pluripotent stem cells (iPSCs). Here, we report the generation of iPSCs that carry the TDP-43 M337V mutation and their differentiation into neurons and functional motor neurons. Mutant neurons had elevated levels of soluble and detergent-resistant TDP-43 protein, decreased survival in longitudinal studies, and increased vulnerability to antagonism of the PI3K pathway. We conclude that expression of physiological levels of TDP-43 in human neurons is sufficient to reveal a mutation-specific cell-autonomous phenotype and strongly supports this approach for the study of disease mechanisms and for drug screening. Several in vitro and in vivo models established the toxicity of ALS-associated TDP-43 mutations, although the underlying mechanism is unclear (9, 10). Most cellular and animal models of ALS and FTLD-TDP pathogenesis involve overexpression of TDP-43 in nonneuronal or nonhuman cells and cannot be used to investigate the selective vulnerability of neurons or key molecular events that are unique to human cells. By contrast, induced pluripotent stem cells (iPSCs) (11-14) coupled with defined in vitro differentiation protocols (15-20) offer a model system to investigate disease mechanisms in a more physiological context. Here, we report the pathological effects of endogenous mutant TDP-43 in iPSC-derived human neurons from an ALS patient carrying the M337V mutation.

With the advent of induced pluripotent stem cell (iPSC) technology, it is now feasible to generate iPSCs with a defined genotype or disease state. When coupled with direct differentiation to a defined lineage, such as hepatic endoderm (HE), iPSCs would revolutionize the way we study human liver biology and generate efficient "off the shelf" models of human liver disease. Here, we show the "proof of concept" that iPSC lines representing both male and female sexes and two ethnic origins can be differentiated to HE at efficiencies of between 70%-90%, using a method mimicking physiological relevant condition. The iPSC-derived HE exhibited hepatic morphology and expressed the hepatic markers albumin and E-cadherin, as assessed by immunohistochemistry. They also expressed alpha-fetoprotein, hepatocyte nuclear factor-4a, and a metabolic marker, cytochrome P450 7A1 (Cyp7A1), demonstrating a definitive endodermal lineage differentiation. Furthermore, iPSC-derived hepatocytes produced and secreted the plasma proteins, fibrinogen, fibronectin, transthyretin, and alpha-fetoprotein, an essential feature for functional HE. Additionally iPSC-derived HE supported both CYP1A2 and CYP3A4 metabolism, which is essential for drug and toxicology testing. Conclusion: This work is first to demonstrate the efficient generation of hepatic endodermal lineage from human iPSCs that exhibits key attributes of hepatocytes, and the potential application of iPSC-derived HE in studying human liver biology. In particular, iPSCs from individuals representing highly polymorphic variants in metabolic genes and different ethnic groups will provide pharmaceutical development and toxicology studies a unique opportunity to revolutionize predictive drug toxicology assays and allow the creation of in vitro hepatic disease models. (HEPATOLOGY 2010;51:329-335.) H uman induced pluripotent stem cells (iPSCs) are reprogrammed mature somatic fibroblasts which represent a pluripotent cell population able to generate all primary cell types in vitro. [1][2][3] The ability to derive iPSCs from an indefinite range of genotypes makes them an attractive resource on which to model liver function reflecting the complexity of polygenic influences on metabolism in vitro. Another facet of iPSC technology is the ability to study the impact of gene polymorphisms in a native chromatin setting and model gene interactions with precision. Therefore iPSC-derived models hold great potential to develop a detailed understanding of human liver disease and metabolism including drug toxicity (for a review, see Dalgetty et al. 4

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