#1 - Totipotency: Scientific References

Dianne N. Irving
Copyright September 23, 2013
Reproduced with Permission

Note: These scientific references are not provided to claim that the separated totipotent cells of the early human embryo -- or any in vitro induced "embryo-like" stem cells -- literally are embryos. Rather it is to scientifically document that many (not all) of these early human embryonic cells are totipotent -- and therefore capable of being reverted back to new whole embryos (if "regulation" is successful") -- as happens in both natural and artificial monozygotic (MZ) twinning. "Regulation" can also heal damaged embryos when cells have been lost or removed. Hopefully these references will be found helpful. (Explanation of "regulation" in later article.)1 ). [Emphases have been used below only to aid those unfamiliar with the science.]

I. Introduction

The term "totipotent" has two meanings. First, it refers to the single-cell human organism/human being/human embryo sexually reproduced by fertilization -- whether done in vivo or in vitro. This new single-cell human being is thus capable of producing all the cells, tissues and organs of an adult human being if allowed to fully develop. Second, it refers to individual cells of the early developing human embryo. To say that many of these early cells (blastomeres) are totipotent is to say that IF they are separated from the original embryo then they are CAPABLE of being reverted back to new embryos IF the natural biological process of "regulation" is successful. If that process is not successful, then those separated totipotent cells remain as cells or simply die. Not new, as the following scientific references document (and they are just the tip of the iceberg). By contrast, the term "pluripotent" implies that, under normal conditions, the cell is not capable of undergoing regulation and being reprogrammed back to a new zygote - even if it were to be separated from the whole organism of which it is a part.

As documented below, many of the cells (blastomeres) of the early developing human embryo before implantation are totipotent - not pluripotent. Many of the cells of the early developing human embryo after implantation are also totipotent - not pluripotent. Precisely because these cells are totipotent -- not pluripotent -- and could undergo regulation, monozygotic (identical) "twinning" (one of many kinds of cloning) can take place, resulting in new asexually reproduced individual living human organisms. This can take place naturally in vivo, or artificially in vitro - e.g., as you will see, by mechanically teasing the blastomeres apart (called "blastomere separation") or splitting the blastocyst in half (called "blastocyst splitting) - as is done in IVF and in ART research laboratories and "infertility" clinics. Both procedures are also referred to as "embryo multiplication".

Because these early human embryonic cells are also diploid (contain "46" nuclear chromosomes), they can also be cloned by nuclear transfer. Embryonic germ line cells are also totipotent2 - not pluripotent -- and therefore can be cloned by "twinning". Because these cells are diploid,3 they can also be cloned by nuclear transfer.

II. Scientific References:

The following selected bibliography on "totipotency" represents only the tip of the iceberg. Only a few of the thousands of items that came up on both PubMed (NIH) and Google searches are included here. The final reference list would be prohibitively long. But even these few references should make it clear to the reader that many of the cells of the early developing human embryo are totipotent - not pluripotent, as often claimed. Since the real experts on this issue are human embryologists, I have listed direct quotations from human embryology textbooks first.

A. Human Embryology Textbooks:

[Note: These human embryology textbooks are obviously addressing the state of the early human embryo that exists in vivo -- within the woman's body. E.g., monozygotic (MZ) twinning -- also called "blastomere separation", "blastocyst splitting", "embryo multiplication" -- is one of many kinds of cloning. It takes place naturally while the developing embryo is still in the woman's fallopian tube traveling toward her uterus (about 5-6 days post-fertilization), as well as during and after implantation in her uterus. MZ twinning also takes place artificially in vitro -- outside the woman's body in IVF and ART research laboratories and "infertility" clinics (usually used when older women have few "eggs" left). [Emphases have been used below only to aid those unfamiliar with the science.]

B. Human Genetics textbooks:

C. IVF/ART textbooks:

D. Genuine Carnegie Stages Online:

E. Scientific Journals, Reports:

F. See also:


1 For more extensive explanations and scientific references, including "regulation", see Irving, "Why Accurate Human Embryology Is Needed To Evaluate Current Trends In Research Involving Stem Cells, Genetic Engineering, Synthetic Biology and Nanotechnology" (November 20, 2012), at: http://www.lifeissues.net/writers/irv/irv_206accuratehumanembryology1.html; also, "Any Human Cell - iPS, Direct Programmed, Embryonic, Fetal or Adult - Can Be Genetically Engineered to Asexually Reproduce New Human Embryos for Purposes of Reproduction ('Infertility')" (November 2011), at: http://www.lifeissues.net/writers/irv/irv_194cellasexuallyreproduce1.html; also, FERTILIZATION and IMPLANTATION of the Early Human Embryo: Accurate Scientific Resources (May 8, 2013), at: http://www.lifeissues.net/writers/irv/irv_212accurateresources1.html; also, The Genuine Carnegie Stages (September 8, 2013), at: http://www.lifeissues.net/writers/irv/irv_216genuinecarnegiestages.html. [Back]

2 Germ line cells Are totipotent (and therefore can be cloned by "twinning"):
Ronan O'Rahilly and Fabiola Muller, Human Embryology & Teratology (New York: Wiley-Liss, 1994); also, O'Rahilly and Muller, ibid. (3rd ed., 2001). [Note: O'Rahilly is one of the originators of the Carnegie Stages of Early Human Embryological Development, and has sat on the international Nomina Embryologica Committee for decades - DNI]: "Primordial germ cells (PGC), or gonocytes, are generally believed to be both extragonadal and extraembryonic in origin. They are difficult to recognize in very young human embryos. Claims for them have been made as early as in the blastocyst, and they are believed to be segregated at latest by 2 1/2 weeks and possibly much earlier. At 4 weeks they can be identified in the umbilical vesicle (yolk sac) and hindgut. A week or so later, they have migrated to the gonads. When the primordial germ cells have settled in the gonad, they become more spherical, stain less intensely with alkaline phosphatase, undergo mitosis, and are then referred to as oogonia or spermatogonia, depending on whether they are situated in an ovary or a testis. ... The unifying feature in the formation of primordial germ cells would seem to be the exemption of those cells from the processes of regional, somatic differentiation.. (pp., 23-24)
... Cells differentiate by the switching off of large portions of their genome. Future somatic cells thereby lose their totipotency and are liable to senescence, whereas germ cells regain their totipotency after meiosis and fertilization. (p. 39)
... Stem cells comprise a small subpopulation of multipotent or pluripotent, ultrastructurally unspecialized, slow-cycling cells that possess the ability of self-renewal and can produce cells that are destined to differentiate. (In contrast, primordial germ cells and those of a morula are totipotent; i.e., they can develop into any type of embryonic tissue and can even form an entirely new embryo) ... In addition to embryonic stem cells from preimplantation blastocysts, stem cells can be obtained from an adult. (p. 136) ... Ethical concerns are intensified by the experimental finding in primates (in contrast to the mouse) that embryonic stem cells are totipotent and can develop into a complete embryo with a primitive streak. ... If the source of the stem cells is a human embryo or fetus, however, ethical and legal issues have to be considered. (pp. 136-137) (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15175501&query_hl=1): Epigenetic modifications serve as an extension of the information content by which the underlying genetic code may be interpreted. ... In mammals, DNA methylation and the modification of histones account for the major epigenetic alterations. Two cycles of DNA methylation reprogramming have been characterised. During germ cell development, epigenetic reprogramming of DNA methylation resets parent-of-origin based genomic imprints and restores totipotency to gametes. [Back]

3 Germ line cells are diploid (and therefore can be cloned by nuclear transfer): Ronan O'Rahilly and Fabiola Muller, Human Embryology & Teratology (3rd ed.) (New York: Wiley-Liss, 2001): Gametogenesis is the production of germ cells (gametes), i.e., spermatozoa and oocytes. ... The gametes are believed to arise by successive divisions from a distinct line of cells (the germ plasm), and the cells that are not directly concerned with gametogenesis are termed somatic. ... Diploid refers to the presence of two sets of homologous chromosomes: 23 pairs, making a total of 46. This is characteristic of somatic and primordial germ cells alike. (p. 19)

Tom Strachan and Andrew Read, Human Molecular Genetics (2nd ed.) (New York: Wiley-Liss, 1999): A subset of the diploid body cells constitute the germ line. These give rise to specialized diploid cells in the ovary and testis that can divide by meiosis to produce haploid gametes (sperm and egg). ... The other cells of the body, apart from the germ line, are known as somatic cells ... most somatic cells are diploid ... (p. 28)

Keith Moore and T.V.N. Persaud, The Developing Human: Clinically Oriented Embryology (6th ed. only) (Philadelphia: W.B. Saunders Company, 1998): Meiosis is a special type of cell division that involves two meiotic cell divisions; it takes place in germ cells only. Diploid germ cells give rise to haploid gametes (sperms and oocytes). (p. 18)

Bruce M. Carlson, Human Embryology & Developmental Biology (St. Louis, MO: Mosby, 1999): "In a mitotic division, each germ cell produces two diploid progeny that are genetically equal." (p. 2) [Back]