• Contents
• Preface

Contents

Chapter 1: Introduction

Chapter 2: Nuclear Exchange in Unicellular Organisms

Chapter 3: The "Fantastical" Experiment in the Metazoan Frog

Chapter 4: Nuclear Potential of Amphibian Cells from Determined and Differentiating Regions

Chapter 5: Nuclear Potential of Differentiated Amphibian Tissues and Cells

Chapter 6: Reversal of Genomic Dormancy of Rana Erythrocyte Nuclei by Implantation into Maturing Oocytes

Chapter 7: Developmental Restrictions and Enhancements in Amphibian Nuclear Trans-plants: Is Totipotency a Tenable Hypothesis?

Chapter 8: Nuclear Potential of Renal Adenocarcinoma of Rana pipiens

Chapter 9: Nuclear Potential of Embryonic Cells from Insects, Ascidians, and Fish

Chapter 10: Nuclear Potential of Mammalian Cells

Chapter 11: Genomic Potential of Differentiated Cells in Other Cellular Systems

Chapter 12: Irreversible DNA Changes Controlling Cell Differentiation

Chapter 13: Molecular Mechanisms Controlling Cell Differentiation Without Irreversible DNA Alterations

Chapter 14: Conclusions and Perspectives

The genesis of this book began during one of the SAWOK (Science as a Way of Knowing Biology) symposia, which were organized by Professor John A. Moore in conjunction with the annual meetings of the American Society of Zoologists. Moore had invited me to participate in the SAWOK Symposium on Developmental Biology held December 1986 in Nashville, Tennessee. Approximately one month after my presentation, I received from Edward E. Lugenbeel, Executive Editor of Columbia University Press, a letter stating that my "presentation in the SAWOK program suggests a book might result from an expansion of this topic," and inquiring about my interest in this project. I much appreciated both invitations. In addition, I thank Ed Lugenbeel and Columbia University Press for their patience in waiting for this project to come to fruition.

Expanding the topic of that presentation--genomic potential of differentiated cells--into a book has been a most pleasurable experience. Scientists in the field have conducted their research primarily by cloning metazoan nuclei into enucleated oocytes, a procedure developed originally in the leopard frog (Rana pipiens) by Robert Briggs and Thomas J. King at the Institute for Cancer Research and the Lankenau Hospital Research Institute (ICR and LHRI), which is now the Fox Chase Cancer Center, in Philadelphia, Pennsylvania. In 1950, Bob Briggs had recruited Tom King to develop a procedure for the transplantation of living embryonic nuclei into enucleated oocytes, and in 1952 they had their first success. As I had joined Bob's laboratory in 1948 as a research assistant primarily involved in cytological studies, I was there from the beginning to witness the excitement surrounding this extraordinary accomplishment. Reflecting on those early years, when financial support of research was meager, I think how courageous it was of the ICR and LHRI to support in part these pioneering experiments. In today's funding climate, such basic research would be deemed much too risky by institutions and granting agencies alike, because there was no guarantee of results.

I also had the pleasure in those early years of collaborating with Bob and Tom on the genomic potential of embryonic endodermal cells and later with Tom on the genomic potential of embryonic neural and adult cancer cells. During part of this time under the sponsorship of Tom King, I completed my graduate studies at the University of Pennsylvania and received the Ph.D. degree.

For the past twenty-eight years, the research in my laboratory has focused primarily on the genomic potential of differentiated frog cells. In addition, I have followed with great interest the extension of nuclear transfer to other metazoan animals, including Drosophila, ascidians, fish, and various mammalian species. Thus it has been an adventure for me to narrate the history of nuclear transplantation and compile the voluminous results of more than forty years of study. I hope I have conveyed some of the joy that accompanied the findings, which I've tried to delineate accurately and objectively.

Only a few books relating to nuclear transplantation in Amphibia--The Control of Gene Expression in Animal Development by John B. Gurdon (1974) and Cloning, Nuclear Transplantation in Amphibia by Robert G. McKinnell (1978)--have been published. Bob McKinnell also performed an important service by narrating for the nonscientist the results of nuclear transplantation studies in Cloning, A Biologist Reports (1979) and its revised edition, Cloning of Frogs, Mice, and Other Animals (1985). In my account, I have built upon and extended the previous coverage of the prehistory and history of nuclear transplantation. In addition, I have discussed certain topics in depth that had previously received little or no attention: nuclear transfers in the unicellular plant Acetabularia and the one-celled animals Amoeba and Stentor, as well as in metazoans such as insects, ascidians, fish, mice, rats, pigs, rabbits, goats, cattle, and sheep. With regard to the latter groups, the early 1980s saw the first successes in mammalian nuclear transplantation, which were achieved with nuclei from preimplantation stages; these and the more recent, impressive results of mammalian cloning are discussed here. Hence this book brings together results of nuclear transplantation studies in unicellular and multicellular organisms from the 1930s to the present.

I devote the majority of the chapters (2-10) to nuclear transplantation studies in oocytes, blastomeres, or somatic cells, because nuclear cloning provides the most complete test of the genomic potential of cells. However, I also look at other experimental systems, such as transdifferentiation, heterokaryons, cell hybrids, and the modulation of the cancer phenotype toward normalcy both in vivo and in vitro (see chapter 11). All these systems have contributed important aspects to our view of genomic potential. Furthermore, as no nucleus from a proven differentiated somatic cell in metazoan animals has yet been shown to be totipotent, I summarize the major molecular controls of cell differentiation, namely, those that involve irreversible genetic changes (see chapter 12) and those that do not (see chapter 13). Finally, I speculate that genomic totipotency is a tenable hypothesis for at least some differentiated somatic cell types (see chapter 14).

Many colleagues generously reviewed and commented on an early draft of the book, and I thank them for their constructive suggestions. I am particularly indebted to Laurence D. Etkin, Robert G. McKinnell, and Nancy Hoffner Orr, who reviewed all the chapters, as well as to colleagues who commented on specific chapters. They include Mary Englebert (1-10), Denise Ferrier (12-14), Neal First (10), Joe Gall (12, 13), Scott Gilbert (1, 5, 6), Thomas J. King (1-5), Keith Latham (10, 13), Tokindo Okada (11), Marko Radic (1 2), Jim Robl (1 0), Bob Savage (11 ), Davor Solter (10, 13), and Zirong Zhao (9), who also translated several articles from Chinese into English. I especially thank Mary Englebert, who translated numerous articles from French into English and helped me in many other ways during the preparation of this book. Wilma Anderson (Director of Archives at the Fox Chase Cancer Center) and numerous scientists graciously provided me with photographs for publication. Many chapters offer photographs of scientists who made important contributions to the field, so that history will have a record of the performers. I thank those who furnished their pictures and regret that not everyone could be included.

I was fortunate that the National Institutes of Health (General Medical Sciences, Genetics Section) and the National Science Foundation (Developmental Biology) provided over the years long-term funding for my research and in turn made this book possible, and I thank them. I also appreciate the sabbatical granted me by the Medical College of Pennsylvania that enabled me to write a significant portion of the book. I thank my collaborators and excellent staff for their contributions to the research, especially Nancy Hoffner Orr, who made so many high-quality contributions for nearly two decades.

Finally, I wish that my parents, who instilled in me the desire to pursue knowledge, could have seen this effort, and I am pleased that my sister, Adelaide, who has been supportive in many ways, did. Last, but not least, I applaud the frog.

Even Hilaire Belloc, a real poet, was fond of the frog:

M. A. Di Berardino
Philadelphia, Pennsylvania
December 1995