Title: "'Virtual Human Embryo'" - Zygote Is Stage 1c, Not Stage 1a"

Dianne N. Irving
Copyright February 6, 2011
Reproduced with Permission

The human zygote at Stage 1c of development is not when a new sexually reproduced human embryo begins to exist. Before that the new human embryo/human being already exists at Stages 1a and 1b.

This critical scientific distinction among the sub-stages of Stage 1 of the Carnegie Stages of Early Human Embryonic Development is now documented once again in an excellent new educational project called "The Virtual Human Embryo". Quoting from the website of the Human Development Anatomy Center:

As a component of the Armed Forces Institute of Pathology, the National Museum of Health and Medicine has a broad mission to educate the public and professionals about health and medicine. As a department of the museum, HDAC continues this mission through collaborations with universities, medical professionals, researchers and other educational projects.

Human Embryo Sections on DVD's for Education

The Human Developmental Anatomy Center is currently in collaboration with the Louisiana State University Medical Center (LSUMC) and Dr. Raymond Gasser on an educational project, "Human Embryo Sections on DVD's for Education". The objective of this project is to provide students, educators and researchers accurate, inexpensive, and accessible visual information on human embryonic development. Aligned digital images of the serial sections of the best, normal human embryos in the Carnegie Collection will be made available on computer disks (DVD's). The DVD's will enable students to learn human embryology from actual embryos; enable educators to produce many varied instructional media on human embryonic development; and provide a valuable reference for developmental biologists.1

This new extensively documented and researched "Virtual Human Embryo" project at Louisiana State University Health Sciences Center, New Orleans, likewise explains its educational mandate:

The Virtual Human Embryo Project was originally developed as a collaboration between embryologist Dr. Raymond Gasser at LSUHSC and the HDAC in Washington DC. The overall aim of the project is to make the Carnegie collection, which is housed at the HDAC, accessible for research and teaching of human embryology. Dr. John Cork at LSUHSC joined the project at its inception as the software developer with a special interest in 3D-reconstruction. The project has two components, both of which are supported by grants from the National Institutes of Health.2

The Virtual Human Embryo is "a digital image database of serially sectioned human embryos from the Carnegie Collection".3 Anyone can access the various stages of the new sexually reproduced developing human embryo by going to the Virtual Human Embryo's "DREM DEMOS" page, click into "Enter", then click into "Demo" on the left of the page.4 Please note that the information provided in the "Virtual Human Embryo" is hardly simply the product of one's subjective opinion of what the accurate scientific facts of human embryology are. Nor is it the product of a "consensus" of some group of scientists, or just some untested "theory", or just represents piles of raw "data" waiting to be subjected to the full scientific method. On the contrary, the information provided on the "Virtual Human Embryo" website constitutes objective scientific facts about the development of the early human embryo that have been processed through the entire scientific method in research around the world, and accepted as objective fact - not subjective opinion -- since at least the institution of the Carnegie Stages in 1942.5 You can't get more objective and accurate than that. It is worth mentioning that, even though some websites with similar scientific information appear to credit the Carnegie Stages by name, when one investigates how critical embryological terms and specific stages are defined on those sites it is clear that they differ quite significantly from the genuine Carnegie Stages. Note too that once an asexually reproduced human embryo begins to exist, his/her biological development would proceed along the same developmental stages as those sexually reproduced.6

Of particular interest is Stage 1 of the "Virtual Human Embryo", because it documents once again that the new sexually reproduced human embryo begins to exist at Stage 1a, not at Stage 1c (the formation of the zygote). Before the formation of the zygote, the new human embryo already exists at Stage 1a (the primitive embryo) and Stage 1b (the ootid).7 Note that the entity at Stage 1a,b,c is not a "potential" human being, nor a "possible" human being, nor a "human-being-on-the-way", nor an "evolving" human being, etc. He or she is already a newly existing actual whole human being, a human organism, a human person.8

The significance of the objective scientific fact that the zygote is not when a new sexually reproduced human being begins to exist is critical, because most of the unethical cloning and other genetic engineering experiments are conducted using the human embryo before the zygote is formed at Stage 1c. That is, these kinds of research experiments are performed when the new human being is already existing at Stage 1a and 1b of his/her development, and usually involve harm and/or destruction of those living human beings. There are literally dozens of different kinds of genetic engineering techniques that use already existing human embryos before the formation of the zygote as sources of "biological materials". For example, in one of a variety of the "pronuclei transfer" cloning techniques, two normal human embryos (a male and a female) are reproduced sexually in vitro. At Stage 1b, when the pronuclei exist in separate envelopments within the embryo, a male pronuclei of one of these new embryos, and a female pronuclei of the other of these new embryos, are extracted and placed together in an enucleated oocyte, and then stimulated to form a new third cloned (asexually reproduced) human being. Both of the two original human embryos are thus destroyed in the process. The new asexually reproduced human embryo is then implanted and brought to term.9

The following are direct quotes from Stage 1 (a,b,c) of the "Virtual Human Embryo", documenting that the new sexually reproduced human being begins to exist at first contact of the sperm and the oocyte at Stage 1a of the new developing human embryo:10


STAGE 1 (a, b, c) of the Developing Embyro:

Stage 1 is the unicellular embryo that contains unique genetic material and is an individually specific cell that has the potential to develop into all of the subsequent stages of a human being. It is the beginning of embryonic life and ontogenetic development that starts when an oocyte, arrested in metaphase of meiosis II, is penetrated by a sperm. This is the first event of fertilization. The embryo has a postovulatory age of approximately one day, is between 0.1 to 0.15 mm in diameter and weighs approximately 0.004 mg .

Fertilization is a series of events that begins when a sperm makes contact with an oocyte and ends with the intermingling of paternal (male) and maternal (female) chromosomes on the spindle at metaphase of the first mitotic division of the single cell. The events of fertilization require just over 24 hrs. to complete and normally take place in the ampulla of the uterine tube.

Stage 1 is divided into three substages; a, b and c. Stage 1a is referred to as the primordial embryo since all the genetic material necessary for the new individual, plus some redundant chromosomes, is now within a single plasmalemma (cell membrane). From the perspective of the female gamete it has also been named the penetrated oocyte. The fertilizing sperm has passed through the zona (capsula) pellucida and its plasmalemma has fused with that of the oocyte. Penetration activates the embryo into resuming its arrested meiosis II and after anaphase it enters telophase with the expulsion of the redundant chromosomes as a second polar body. This marks the beginning of Stage 1b in which the single-cell is referred to as the pronuclear embryo. From the perspective of the female gamete it has also been named the ootid because its female component is haploid like a spermatid. However, in the pronuclear embryo there are two separate haploid components: one maternal, or female, pronucleus and one paternal, or male, pronucleus. The pronuclei move toward each other and eventually compress their envelops where they lie adjacent near the center of the cell. Stage 1c is the last phase of fertilization and exists for a relatively short period. The pronuclear envelopes disappear and the parental chromosomes that were contained in separate pronuclei come together in a process called syngamy thereby establishing the genome of the embryo. The one-cell Stage 1c embryo is named the syngamic embryo or zygote. The chromosomes assume positions on the rapidly formed first mitotic spindle in preparation for cleavage.

The Carnegie collection contains no stage 1 specimens. The database for this stage is therefore limited to previously published images of in vitro specimens that best show the progression of development. Only images of those specimens that the authors considered healthy were selected for inclusion in the database. Grateful appreciation is expressed to all of the authors and their publishers for their generosity in permitting the use of their images in the database.

A measuring bar is present in most of the light micrographs (LM). The length of the measuring bar is based on a diameter of the one cell (including the zona pellucida) of 175 ??m before fixation. The diameter of the cell, without the zona pellucida, is approximately 100 ??m before fixation. The embryo undergoes shrinkage with fixation and embedding. Since the cytoplasm is more affected than the zona pellucida the subzonal (perivitelline) space becomes accentuated in fixed specimens. The original magnification is given in the legend of most scanning (SEM) and transmission (TEM) electron micrographs.

In Vitro 1a Specimens (click here to view figures)

In the primordial embryo the plasma membranes of the fertilizing gametes become confluent (Fig. 4). Non-fertilizing sperm may be present in the zona pellucida or in the subzonal space. The cytoplasm of the embryo protrudes where the fertilizing sperm enters. The protrusion is referred to as the fertilization cone (Fig. 3). It is devoid of microvilli and has numerous microfilaments forming a conspicuous band beneath the cell membrane. It later retracts supposedly drawing the sperm deep into the cytoplasm.

Once inside the cytoplasm the original envelope of the sperm vesiculates and is gradually dismantled. The head of the fertilizing sperm becomes decondensed and swells. Pronuclei are not yet present but a wave of granularity moves throughout the cytoplasm in 2 to 10 circular rotations. Some of the rotations are clockwise and some are counter clockwise. The movement lasts for twenty or more minutes and is referred to as the cortical reaction. The reaction involves the exocytosis of the contents of cortical granules. The membrane of the granules fuses with the overlying cell membrane then burst open releasing their contents into the subzonal space by a process similar to cell secretion (Figs. 13-15). Cortical granule release occurs three hours after sperm / oocyte fusion. Once the cortical granule contents are released into the subzonal space they interact with the inner part of the zona pellucida thus preventing further entrance of sperm into the oocyte and inhibiting polyspermia. The interaction is called the zonal reaction. (Fig. 16)

The second miotic division is completed at this time with the release of the second polar body into the subzonal space. Since the cytoplasm contains the genetic material from both the mother and father it is now technically an embryo (Figs. 1, 2, 3f, 7-12).

In Vitro 1b Specimens (click here to view figures)

The unique feature of pronuclear embryos is the presence of pronuclei which appear within 11 hours of in vitro insemination. The pronuclei each measure approximately 30 ??m in diameter before fixation. The paternal (male) and maternal (female) pronuclei usually form simultaneously (Figs. 11, 12). The paternal pronucleus is usually larger and forms near the site where the sperm entered (fertilization cone); the maternal pronucleus forms near the site where the second polar body is extruded.

After their formation the pronuclei are located a distance from each other but subsequently each moves toward the center of the cell (Figs. 2, 3). By 15 hours after in vitro insemination they lie close to one another (Fig. 6). They remain closely associated until the onset of syngamy (See below). As they approach one another, adjacent areas of each pronuclear envelope appear to flatten out. At the same time nucleoli move from random locations within each pronucleus to line up in the flattened pronuclear envelope regions (Figs. 6, 7). Nucleoli vary in size and number from as few as one to as many as nine. The envelope of the maternal pronucleus often begins to break down before the paternal one. The envelopes of the pronuclei do not fuse or interlock.

A straight line can be drawn from the polar bodies through the cytoplasm that divides the cell into equal parts. This line is called the polar axis (or anterior-posterior polar axis) and roughly indicates the location of the first cleavage plane. The pronuclei rotate into the polar axis and align along it (Figs. 4, 5). This is considered the correct position for syngamy and the first cleavage.

In Vitro 1c Specimens (click here to view figures)

The stage 1c embryo is called the syngamic embryo or zygote and is the last phase of fertilization. It is sometimes called a founder cell because it gives rise to embryonic stem cells. Stage 1c occurs about 20 hours after in vitro insemination but is elusive since it exists for only a brief period. The pronuclei quickly disappear when their envelopes break down (Figs. 1, 2, 5). Groups of chromosomes that were in the pronuclei assume positions in pairs on the rapidly formed first cleavage spindle thereby bringing about syngamy and the establishment of the integrated genome of the embryo. The chromosomes lie in an agranular zone in the central cytoplasm. Since a nuclear envelope does not form, a nucleus is not present at this substage.



1 See the website of the Human Development Anatomy Center: http://nmhm.washingtondc.museum/collections/hdac/Education_Projects.htm. This is also the home of the Carnegie Stages of Early Human Embryonic Development; see Carnegie Stage 1a,b,c at: http://nmhm.washingtondc.museum/collections/hdac/stage1.pdf; see all 23 stages of the early developing human embryo at: http://nmhm.washingtondc.museum/collections/hdac/Select_Stage_and_Lab_Manual.htm. Click into the "textbook" at the bottom left side of the screen to access more extensive details of each stage and the scientific references. [Back]

2 See LSUHSC's "Virtual Human Embryo" at: http://virtualhumanembryo.lsuhsc.edu/. [Back]

3 See: http://virtualhumanembryo.lsuhsc.edu/DREM/DREM_home.htm. [Back]

4 Ibid. [Back]

5 See D. N. Irving, "The Carnegie Stages of Early Human Embryonic Development: Chart of all 23 Stages, and Detailed Descriptions of Carnegie Stages 1-6" (April 22, 2006), at: http://www.lifeissues.net/writers/irv/irv_123carnegiestages1.html; see also, Irving and Kischer, "Scientific Response to Criticism of the California Human Rights Amendment as 'Protecting Fertilized Eggs'" (Dec. 9, 2009), at: http://www.lifeissues.net/writers/irv/irv_173californiaamendment.html, and at: http://www.lifeissues.net/writers/irv/irv_175responsecalifornia.html. [Back]

6 See objective scientific references for asexual human reproduction in, e.g., Irving and Kischer, "Scientific Response to Criticism of the California Human Rights Amendment as Protecting Fertilized Eggs'" (Dec. 9, 2009), at: http://www.lifeissues.net/writers/irv/irv_173californiaamendment.html, and at: http://www.lifeissues.net/writers/irv/irv_175responsecalifornia.html. [Back]

7 See Stage 1: Introduction: at http://virtualhumanembryo.lsuhsc.edu/demos/Stage1/Intro_pg/Intro.htm. [Back]

8 For an extensive analysis of the various historical attempts at deconstructing the accurate objectively documented science of human embryology in science, philosophy, theology, and bioethics over the last 40 years, see D. N. Irving, "Human Embryology and Church Teachings" (September 15, 2008), at: http://www.lifeissues.net/writers/irv/em/em_132embryologychurch1.html; also published in The New Catholic Encyclopedia, 2nd ed., Supplement 2009, (Detroit: Gayle), pp. 287-312, as "Embryology, Human"; see http://www.gale.cengage.com/NCE/. [Back]

9 For example, see Craven et al, "Pronuclear transfer in human embryos to prevent transmission of mitochondrial DNA disease", Nature, 2010 May 6;465(7294):82-5. Epub 2010 Apr 14; PMID: 20393463; at: http://www.ncbi.nlm.nih.gov/pubmed/20393463; Bredenoord AL, Pennings G, de Wert G, "Ooplasmic and nuclear transfer to prevent mitochondrial DNA disorders: conceptual and normative issues", Hum Reprod Update. 2008 Nov-Dec;14(6):669-78. Epub 2008 Sep 4, PMID: 18772267, at: http://www.ncbi.nlm.nih.gov/pubmed/18772267. Literally hundreds of studies involving variations on "human pronuclei transfer" and subsequent birth can be accessed by searches at PubMed, at: http://www.ncbi.nlm.nih.gov/pubmed. [Back]

10 See "Introduction" to Stage 1: http://virtualhumanembryo.lsuhsc.edu/demos/Stage1/Intro_pg/Intro.htm; emphases added. [Back]

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