25th ANNIVERSARY OF CLONING BY SOMATIC-CELL NUCLEAR TRANSFER: Nuclear transfer and the development of genetically modified/gene edited livestock.

The birth and adult development of 'Dolly' the sheep, the first mammal produced by the transfer of a terminally differentiated cell nucleus into an egg, provided unequivocal evidence of nuclear equivalence among somatic cells. This ground-breaking experiment challenged a long-standing dogma of irreversible cellular differentiation that prevailed for over a century and enabled the development of methodologies for reversal of differentiation of somatic cells, also known as nuclear reprogramming. Thanks to this new paradigm, novel alternatives for regenerative medicine in humans, improved animal breeding in domestic animals and approaches to species conservation through reproductive methodologies have emerged. Combined with the incorporation of new tools for genetic modification, these novel techniques promise to (i) transform and accelerate our understanding of genetic diseases and the development of targeted therapies through creation of tailored animal models, (ii) provide safe animal cells, tissues and organs for xenotransplantation, (iii) contribute to the preservation of endangered species, and (iv) improve global food security whilst reducing the environmental impact of animal production. This review discusses recent advances that build on the conceptual legacy of nuclear transfer and - when combined with gene editing - will have transformative potential for medicine, biodiversity and sustainable agriculture. We conclude that the potential of these technologies depends on further fundamental and translational research directed at improving the efficiency and safety of these methods.

25th ANNIVERSARY OF CLONING BY SOMATIC CELL NUCLEAR TRANSFER: Generation of genetically engineered livestock using somatic cell nuclear transfer.

Genetic engineering (GE) of livestock initially has been accomplished primarily using pronuclear microinjection into zygotes (1985-1996). The applications of the technology were limited due to low integration efficiency, aberrant transgene expression resulting from random integration and the presence of genetic mosaicism in transgenic founder animals. Despite enormous efforts to established embryonic stem cells (ESCs) for domestic species, the ESC GE technology does not exist for livestock. Development of somatic cell nuclear transfer (SCNT) has bypassed the need in livestock ESCs and revolutionized the field of livestock transgenesis by offering the first cell-based platform for precise genetic manipulation in farm animals. For nearly two decades since the birth of Dolly (1996-2013), SCNT was the only method used for the generation of knockout and knockin livestock. Arrival of CRISPRS/Cas9 system, a new generation of gene-editing technology, gave us an ability to introduce precise genome modifications easily and efficiently. This technological advancement accelerated production of GE livestock by SCNT and reinstated zygote micromanipulation as an important GE approach. The primary advantage of the SCNT technology is the ability to confirm in vitro that the desired genetic modification is present in the somatic cells prior to animal production. The edited cells could also be tested for potential off-target mutations. Additionally, this method eliminates the risk of genetic mosaicism frequently observed following zygote micromanipulation. Despite its low efficiency, SCNT is a well-established procedure in numerous laboratories around the world and will continue to play an important role in the GE livestock field.

25th ANNIVERSARY OF CLONING BY SOMATIC-CELL NUCLEAR TRANSFER Twenty-five years after Dolly: how far have we come?

For more than a century, the scientific consensus stated that a nucleus from a terminally differentiated cell would not be able to control the development of offspring. This theory was refuted by the birth of Dolly, the first animal generated by nuclear transfer using an adult somatic cell as a nuclear donor. Following this paradigm shift, a wide variety of animals has been cloned using somatic cell nuclear transfer. Coupled with modern genome engineering technology, somatic cell nuclear transfer has become the method of choice for the generation of genetically modified farm animals. This has opened new opportunities to study the function of genes and has led to the establishment of animal models for a variety of human conditions and diseases or to improve the health of livestock animals.

25th ANNIVERSARY OF CLONING BY SOMATIC-CELL NUCLEAR TRANSFER: Current applications of SCNT in advanced breeding and genome editing in livestock.

SCNT (somatic cell nuclear transfer) has complemented the toolbox of ARTs offering yet another technique to reproduce animals in an unprecedented way. Despite remarkable achievements, SCNT suffers low efficiency, high pregnancy losses and higher than normal stillbirth rates that makes it an expensive technique to reproduce animals. Moreover, due to welfare issues associated with gestation and the newborn offspring, it is banned in some countries. It has become evident that these problems are of epigenetic nature associated with incomplete genome reprogramming, observed more frequently in ruminants and less often and of minor degree in pigs and horses. Genome editing is enormously benefiting from SCNT to turn genome edited cells into animals, even if zygote microinjection of CRISPR/Cas9 will become an alternative route in some occasions. SCNT will also be a route to reprogram somatic cell to pluripotency since bona fide iPSC in livestock are missing while embryonic stem cells have been now established. This opens the way to other technologies like the development of artificial gametes or interspecies nuclear transfer. To strengthen its commercial applications, SCNT will face three major challenges, that is, intellectual property (extremely unclear in genome editing), regulatory approval by the relevant authorities of the resuting potential products and finally, acceptance by the public who will eventually decide with its behavior the life or the death of the technology.

25th ANNIVERSARY OF CLONING BY SOMATIC-CELL NUCLEAR TRANSFER: Scientific and technological approaches to improve SCNT efficiency in farm animals and pets.

The birth of Dolly through somatic cell nuclear transfer (SCNT) was a major scientific breakthrough of the last century. Yet, while significant progress has been achieved across the technics required to reconstruct and in vitro culture nuclear transfer embryos, SCNT outcomes in terms of offspring production rates are still limited. Here, we provide a snapshot of the practical application of SCNT in farm animals and pets. Moreover, we suggest a path to improve SCNT through alternative strategies inspired by the physiological reprogramming in male and female gametes in preparation for the totipotency required after fertilization. Almost all papers on SCNT focused on nuclear reprogramming in the somatic cells after nuclear transfer. We believe that this is misleading, and even if it works sometimes, it does so in an uncontrolled way. Physiologically, the oocyte cytoplasm deploys nuclear reprogramming machinery specifically designed to address the male chromosome, the maternal alleles are prepared for totipotency earlier, during oocyte nuclear maturation. Significant advances have been made in remodeling somatic nuclei in vitro through the expression of protamines, thanks to a plethora of data available on spermatozoa epigenetic modifications. Missing are the data on large-scale nuclear reprogramming of the oocyte chromosomes. The main message our article conveys is that the next generation nuclear reprogramming strategies should be guided by insights from in-depth studies on epigenetic modifications in the gametes in preparation for fertilization.

25th ANNIVERSARY OF CLONING BY SOMATIC-CELL NUCLEAR TRANSFER: Epigenetic abnormalities associated with somatic cell nuclear transfer.

Twenty-five years have passed since the birth of Dolly the sheep, the first mammalian clone produced by adult somatic cell nuclear transfer (SCNT). During that time, the main thrust of SCNT-related research has been the elucidation of SCNT-associated epigenetic abnormalities and their correction, with the aim of improving the efficiency of cloned animal production. Through these studies, it has become clear that some epigenomic information can be reprogrammed by the oocyte, while some cannot. Now we know that the imprinting memories in the donor genome, whether canonical (DNA-methylation-dependent) or noncanonical (H3K27me3-dependent), are not reprogrammed by SCNT. Thus, SCNT-derived embryos have the normal canonical imprinting and the erased noncanonical imprinting, both being inherited from the donor cells. The latter can cause abnormal phenotypes in SCNT-derived placentas arising from biallelic expressions of noncanonically imprinted genes. By contrast, repressive epigenomic information, such as DNA methylation and histone modifications, might be more variably reprogrammed, leaving room for technical improvements. Low-input analytical technologies now enable us to analyze the genome of gametes and embryos in a high-throughput, genome-wide manner. These technologies are being applied rapidly to the SCNT field, providing evidence for incomplete reprogramming of the donor genome in cloned embryos or offspring. Insights from the study of epigenetic phenomena in SCNT are highly relevant for our understanding of the mechanisms of genomic reprogramming that can induce totipotency in the mammalian genome.

Logros y conflictos en la investigación con células troncales / Achievements and struggles in stem-cell investigation research

Se relatan circunstancias, peripecias y conflictos que han rodeado a varios de los investigadores que han protagonizado el avance de los conocimientos sobre las células troncales a lo largo de cien años, desde el establecimiento del dogma de la inmortalidad celular hasta las técnicas desarrolladas para obtenerlas y utilizarlas en medicina regeneradora. En este último aspecto, se incluye un breve análisis de las perspectivas previstas para las células pluripotentes inducidas (iPS) en relación con las células troncales producidas por transferencia nuclear (NT-ESC) y la producción de embriones humanos por transferencia nuclear de células somáticas (embriones SCNT) (AU)

This report describes events, circumstances and conflicts that have surrounded to several researchers protagonists of the advances on the stem cells knowledge along a hundred of years, from the cell immortality dogma to the discovery of tecnics to produce them to be used in regenerative medicine. At this respect, a brief analysis of the expected outlook for induced human pluripotent cells (iPS) is included and compared with nuclear transfer human stem cells (NTESC) and production of human enbryos by somatic cell nuclear transfer (SCNT embryos) (AU)

The promise of dog cloning.

Dog cloning as a concept is no longer infeasible. Starting with Snuppy, the first cloned dog in the world, somatic cell nuclear transfer (SCNT) has been continuously developed and used for diverse purposes. In this article we summarise the current method for SCNT, the normality of cloned dogs and the application of dog cloning not only for personal reasons, but also for public purposes.

Pluripotent stem cells and livestock genetic engineering.

The unlimited proliferative ability and capacity to contribute to germline chimeras make pluripotent embryonic stem cells (ESCs) perfect candidates for complex genetic engineering. The utility of ESCs is best exemplified by the numerous genetic models that have been developed in mice, for which such cells are readily available. However, the traditional systems for mouse genetic engineering may not be practical for livestock species, as it requires several generations of mating and selection in order to establish homozygous founders. Nevertheless, the self-renewal and pluripotent characteristics of ESCs could provide advantages for livestock genetic engineering such as ease of genetic manipulation and improved efficiency of cloning by nuclear transplantation. These advantages have resulted in many attempts to isolate livestock ESCs, yet it has been generally concluded that the culture conditions tested so far are not supportive of livestock ESCs self-renewal and proliferation. In contrast, there are numerous reports of derivation of livestock induced pluripotent stem cells (iPSCs), with demonstrated capacity for long term proliferation and in vivo pluripotency, as indicated by teratoma formation assay. However, to what extent these iPSCs represent fully reprogrammed PSCs remains controversial, as most livestock iPSCs depend on continuous expression of reprogramming factors. Moreover, germline chimerism has not been robustly demonstrated, with only one successful report with very low efficiency. Therefore, even 34 years after derivation of mouse ESCs and their extensive use in the generation of genetic models, the livestock genetic engineering field can stand to gain enormously from continued investigations into the derivation and application of ESCs and iPSCs.

Genetically engineered livestock for biomedical models.

To commemorate Transgenic Animal Research Conference X, this review summarizes the recent progress in developing genetically engineered livestock species as biomedical models. The first of these conferences was held in 1997, which turned out to be a watershed year for the field, with two significant events occurring. One was the publication of the first transgenic livestock animal disease model, a pig with retinitis pigmentosa. Before that, the use of livestock species in biomedical research had been limited to wild-type animals or disease models that had been induced or were naturally occurring. The second event was the report of Dolly, a cloned sheep produced by somatic cell nuclear transfer. Cloning subsequently became an essential part of the process for most of the models developed in the last 18 years and is stilled used prominently today. This review is intended to highlight the biomedical modeling achievements that followed those key events, many of which were first reported at one of the previous nine Transgenic Animal Research Conferences. Also discussed are the practical challenges of utilizing livestock disease models now that the technical hurdles of model development have been largely overcome.

Genetically engineered livestock for agriculture: a generation after the first transgenic animal research conference.

At the time of the first Transgenic Animal Research Conference, the lack of knowledge about promoter, enhancer and coding regions of genes of interest greatly hampered our efforts to create transgenes that would express appropriately in livestock. Additionally, we were limited to gene insertion by pronuclear microinjection. As predicted then, widespread genome sequencing efforts and technological advancements have profoundly altered what we can do. There have been many developments in technology to create transgenic animals since we first met at Granlibakken in 1997, including the advent of somatic cell nuclear transfer-based cloning and gene editing. We can now create new transgenes that will express when and where we want and can target precisely in the genome where we want to make a change or insert a transgene. With the large number of sequenced genomes, we have unprecedented access to sequence information including, control regions, coding regions, and known allelic variants. These technological developments have ushered in new and renewed enthusiasm for the production of transgenic animals among scientists and animal agriculturalists around the world, both for the production of more relevant biomedical research models as well as for agricultural applications. However, even though great advancements have been made in our ability to control gene expression and target genetic changes in our animals, there still are no genetically engineered animal products on the market for food. World-wide there has been a failure of the regulatory processes to effectively move forward. Estimates suggest the world will need to increase our current food production 70 % by 2050; that is we will have to produce the total amount of food each year that has been consumed by mankind over the past 500 years. The combination of transgenic animal technology and gene editing will become increasingly more important tools to help feed the world. However, to date the practical benefits of these technologies have not yet reached consumers in any country and in the absence of predictable, science-based regulatory programs it is unlikely that the benefits will be realized in the short to medium term.

Emotional reactions to human reproductive cloning.

BACKGROUND: Extant surveys of people's attitudes towards human reproductive cloning focus on moral judgements alone, not emotional reactions or sentiments. This is especially important given that some (especially Leon Kass) have argued against such cloning on the ground that it engenders widespread negative emotions, like disgust, that provide a moral guide. OBJECTIVE: To provide some data on emotional reactions to human cloning, with a focus on repugnance, given its prominence in the literature. METHODS: This brief mixed-method study measures the self-reported attitudes and emotions (positive or negative) towards cloning from a sample of participants in the USA. RESULTS: Most participants condemned cloning as immoral and said it should be illegal. The most commonly reported positive sentiment was by far interest/curiosity. Negative emotions were much more varied, but anxiety was the most common. Only about a third of participants selected disgust or repugnance as something they felt, and an even smaller portion had this emotion come to mind prior to seeing a list of options. CONCLUSIONS: Participants felt primarily interested and anxious about human reproductive cloning. They did not primarily feel disgust or repugnance. This provides initial empirical evidence that such a reaction is not appropriately widespread.

Somatic cell nuclear transfer: origins, the present position and future opportunities.

Nuclear transfer that involves the transfer of the nucleus from a donor cell into an oocyte or early embryo from which the chromosomes have been removed was considered first as a means of assessing changes during development in the ability of the nucleus to control development. In mammals, development of embryos produced by nuclear transfer depends upon coordination of the cell cycles of donor and recipient cells. Our analysis of nuclear potential was completed in 1996 when a nucleus from an adult ewe mammary gland cell controlled development to term of Dolly the sheep. The new procedure has been used to target the first precise genetic modification into livestock; however, the greatest inheritance of the Dolly experiment was to make biologists think differently. If unknown factors in the recipient oocyte could reprogramme the nucleus to a stage very early in development then there must be other ways of making that change. Within 10 years, two laboratories working independently established protocols by which the introduction of selected transcription factors changes a small proportion of the treated cells to pluripotent stem cells. This ability to produce 'induced pluripotent stem cells' is providing revolutionary new opportunities in research and cell therapy.

Genome engineering in cattle: recent technological advancements.

Great strides in technological advancements have been made in the past decade in cattle genome engineering. First, the success of cloning cattle by somatic cell nuclear transfer (SCNT) or chromatin transfer (CT) is a significant advancement that has made obsolete the need for using embryonic stem (ES) cells to conduct cell-mediated genome engineering, whereby site-specific genetic modifications can be conducted in bovine somatic cells via DNA homologous recombination (HR) and whereby genetically engineered cattle can subsequently be produced by animal cloning from the genetically modified cells. With this approach, a chosen bovine genomic locus can be precisely modified in somatic cells, such as to knock out (KO) or knock in (KI) a gene via HR, a gene-targeting strategy that had almost exclusively been used in mouse ES cells. Furthermore, by the creative application of embryonic cloning to rejuvenate somatic cells, cattle genome can be sequentially modified in the same line of somatic cells and complex genetic modifications have been achieved in cattle. Very recently, the development of designer nucleases-such as zinc finger nucleases (ZFNs) and transcription activator-like effector nuclease (TALENs), and clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9)-has enabled highly efficient and more facile genome engineering in cattle. Most notably, by employing such designer nucleases, genomes can be engineered at single-nucleotide precision; this process is now often referred to as genome or gene editing. The above achievements are a drastic departure from the traditional methods of creating genetically modified cattle, where foreign DNAs are randomly integrated into the animal genome, most often along with the integrations of bacterial or viral DNAs. Here, I review the most recent technological developments in cattle genome engineering by highlighting some of the major achievements in creating genetically engineered cattle for agricultural and biomedical applications.

¿Un paso adelante hacia la clonación humana con fines terapéuticos?: una adenda / A step forward towards human cloning for therapeutic purposes?: an addendum

En el presente trabajo se analiza el estado actual de las investigaciones para la obtención de embriones humanos clónicos por transferencia nuclear de células somáticas y de las células troncales embrionarias (células NT-ES) y su posible utilización con fines terapéuticos y su comparación con las células troncales pluripotentes inducidas (células iPS). Se hace referencia también a la reprogramación directa como método alternativo. El texto se presenta como una adenda a una revisión anterior del propio autor

Present investigations carried out to produce human embryos by somatic cell nuclear transfer (SCNT embryos) and nuclear transfer human embryo stem cells (NT-ESC) and their use in regenerative medicine are analyzed and compared with the induced pluripotent cells (iPS). A reference to the direct reprogramming technique is made. The text is presented as an addendum to an author's previous review