Ian Wilmut (1944-2023).

Embryologist who cloned Dolly the sheep.

A journey through horse cloning.

Interest in equine somatic cell nuclear transfer technology has increased significantly since the first equid clones were produced in 2003. This is demonstrated by the multiple commercial equine cloning companies having produced numerous cloned equids to date; worldwide, more than 370 cloned horses have been produced in at least six different countries. Equine cloning can be performed using several different approaches, each with different rates of success. In this review we cover the history and applications of equine cloning and summarise the major scientific advances in the development of this technology in horses. We explain the advantages and disadvantages of different procedures to produce cloned equine embryos and describe the current status of equine clone commercialisation, along with observations of differences in regional breed association registration regulations.

Nuclear transplantation, the conservation of the genome, and prospects for cell replacement.

Initial nuclear transplantation experiments in Xenopus eggs provided the first evidence for the conservation of the genome after cellular differentiation. This Discovery-in-Context Review recounts the early experiments that led to successful nuclear transfer in amphibians and the establishment of totipotency of a differentiated cell and shows how these discoveries paved the way for similar cloning experiments in other organisms.

Cancer, conflict, and the development of nuclear transplantation techniques.

The technique of nuclear transplantation - popularly known as cloning - has been integrated into several different histories of twentieth century biology. Historians and science scholars have situated nuclear transplantation within narratives of scientific practice, biotechnology, bioethics, biomedicine, and changing views of life. However, nuclear transplantation has never been the focus of analysis. In this article, I examine the development of nuclear transplantation techniques, focusing on the people, motivations, and institutions associated with the first successful nuclear transfer in metazoans in 1952. The conflict between embryologists and geneticists over the mechanisms of differentiation motivated Robert Briggs to pursue nuclear transplantation experiments as a way to resolve the debate. Briggs worked at the Lankenau Hospital Research Institute, a research facility devoted to the study of cancer. The goal of understanding cancer would play a role in the development of the technique, and the story of nuclear transplantation sheds light on the role that biomedical contexts play in biological research in the second half of the twentieth century.

The ups and downs of somatic cell nucleus transfer (SCNT) in humans.

Achieving successful somatic cell nuclear transfer (SCNT) in the human and subhuman primate relative to other mammals has been questioned for a variety of technical and logistical issues. Here we summarize the gradual evolution of SCNT technology from the perspective of oocyte quality and cell cycle status that has recently led to the demonstration of feasibility in the human for deriving chromosomally normal stem cells lines. With these advances in hand, prospects for therapeutic cloning must be entertained in a conscientious, rigorous, and timely fashion before broad spectrum clinical applications are undertaken.

Induction of pluripotency.

The molecular and phenotypic irreversibility of mammalian cell differentiation was a fundamental principle of developmental biology at least until the 1980s, despite numerous reports dating back to the 1950s of the induction of pluripotency in amphibian cells by nuclear transfer (NT). Landmark reports in the 1980s and 1990s in sheep progressively challenged this dogmatic assumption; firstly, embryonic development of reconstructed embryos comprising whole (donor) blastomeres fused to enucleated oocytes, and famously, the cloning of Dolly from a terminally differentiated cell. Thus, the intrinsic ability of oocyte-derived factors to reverse the differentiated phenotype was confirmed. The concomitant elucidation of methods for human embryonic stem cell isolation and cultivation presented opportunities for therapeutic cell replacement strategies, particularly through NT of patient nuclei to enucleated oocytes for subsequent isolation of patient-specific (autologous), pluripotent cells from the resulting blastocysts. Associated logistical limitations of working with human oocytes, in addition to ethical and moral objections prompted exploration of alternative approaches to generate autologous stem cells for therapy, utilizing the full repertoire of factors characteristic of pluripotency, primarily through cell fusion and use of pluripotent cell extracts. Stunningly, in 2006, Japanese scientists described somatic cell reprogramming through delivery of four key factors (identified through a deductive approach from 24 candidate genes). Although less efficient than previous approaches, much of current stem cell research adopts this focused approach to cell reprogramming and (autologous) cell therapy. This chapter is a quasi-historical commentary of the various aforementioned approaches for the induction of pluripotency in lineage-committed cells, and introduces transcriptional and epigenetic changes occurring during reprogramming.

The cloning of a frog.

It is relatively unusual for the Nobel Prize in Physiology or Medicine to be made, to a large extent, on the basis of a single author paper, published over 50 years ago, for work carried out by a graduate student. This was largely true of a paper published in 1962 in the journal Development (called at that time the Journal of Embryology and Experimental Morphology). The main subject of that paper was the production of normal tadpoles from the nuclei of intestinal epithelium cells of Xenopus laevis. In view of this unusual situation, I have been invited to comment on the 1962 paper.

The egg and the nucleus: a battle for supremacy.

Sir John Gurdon and Professor Shinya Yamanaka were the recipients of the 2012 Nobel Prize for Physiology or Medicine. This Spotlight article is a commentary on the early nuclear transplant work in Xenopus, which was very important for the Nobel award in 2012, and the influence of this work on the reprogramming field.