When Does a Human Life Begin? 17 TimepointsJ.K. Findlay, M.L. Gear, P.J. Illingworth, B.C. Garbage, G. Kay, A.H. Mackerras, A. Pope, H.S. Rothenfluh, L. Wilton, the human embryo: the biological definition, Human Reproduction, Volume 22, Issue 4, April 2007, Pages 905-911,
This paper defines the human embryo from the biological point which takes into account emerging technologies in reproductive science. The paper does not consider the legal, moral, religious or social views. As the definition of a human embryo must reflect the multifactorial process of development, the approach has been adopted which combines recognition observed events with the potential for further development. It recognizes that the process of fertilization and development are not static, and the status of the embryo can only be determined by observation of a particular marker. , Following the definition of biological 'human embryo' proposed
A human embryo is discrete entities arising either from:
mitotic first when fertilization oocytes human with human sperm is complete or
another process that initiates conducted the development of biological entities to the nuclear genome of human or altered nuclear genome of man who has the potential to develop up to, or beyond, the stage where that appears primitive streak,
the definition of a human embryo typically includes entities created by the fertilization of a human oocyte by a human sperm. However, there are a number of the latest technological developments have allowed to create an entity called an embryo by other means, such as somatic cell nuclear transfer (SCNT) and induced parthenogenesis. Because these examples and evolving technology, it is considered appropriate to revisit the biological definition of 'human embryo'.
The last decade has seen the development of reproductive technologies has led to debate over whether the entity that may, or could theoretically be produced will fall within the current definition of an embryo. The definition is based on the potential for further development may catch an entity that may not be covered by the definitions that determine the critical early developmental time points (eg, completion of fertilization). For example, since some of the technology does not involve fertilization, it has been proposed that the generated entity can not be considered as an embryo under some legal definitions (). It has been argued although in some cases there is a possibility that if it is placed into the uterine environment that is correct, eligible individuals can theoretically be produced. To date, there is no credible evidence of any cloned human has born. However, the fact that in several species of mammals, such as mice, sheep and cows, SCNT has resulted in live births that develop into a healthy adult animals would suggest that this can be achieved in humans.
When considering what defines an embryo in the light of technological advances recently, it is important that the definition does not become so widely for Encompass human cells or cellular structures that traditionally have not considered before becoming embryo. For example, it has been argued () that human somatic cells, which theoretically core can be inserted into a living entity after many manipulations, as shown by the success of SCNT, can be considered as a potential embryo. Furthermore, hydatidiform mole, which may be derived from an embryo, the embryo has traditionally not been considered.
The table summarizes the development potential and the genetic constitution of the entity produced as a result of the emerging technologies in the science and technology of reproduction as a horizon based on indications from the literature. For comparison, the embryo arising from the natural reproductive process are also included. From the information presented can be concluded that emerging technologies can generate entity: It is instructive to examine the main differences between the entities generated by the natural reproductive processes and emerging technologies to determine whether the latter can be defined as a human embryo.
has the potential to implant or result in live births and / or
not contribute genetic information of sperm and oocytes and / or
may contain DNA from two different species.
development potential and genetic contribution entities produced either by the natural process of fertilization or as a result of the emerging technologies in the science of reproduction
a
b
cFootnote 25 in
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t.
the development potential and genetic contributions from entities that generated either by the natural process of fertilization or as a result of the emerging technologies in the science of reproduction
a
b
cFootnote 25 in
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t.
animal models have demonstrated that SCNT blastocysts have the potential to implant and develop into a live birth (). It is therefore reasonable to assume that human SCNT blastocysts also has the potential to develop into a viable individual if placed in the right environment.
It has been shown that transferring the blastomere worthy of preimplantation embryo development were slow to be empty zona pellucida generate aggregate preimplantation structure that can develop to the blastocyst stage, from which the cells can be derived human embryonic stem (). Although it remains to be tested whether the blastocyst aggregates such as (reproduction techniques 6) can embed and establish a viable pregnancy, it is theoretically feasible.
In the mouse model, significant progress has been made in the generation of gametes from embryonic stem cells (;;;). Generation of fully functional male gametes from embryonic stem cells ex vivo have recently demonstrated (). Another approach is for the human oocyte is derived in vitro from cells of the ovarian surface epithelium (). It is yet to be proved whether human oocytes produced using this strategy (reproductive techniques 13 and 14) can be fertilized and grow to form a viable pregnancy. The use of these gametes fertilization can result in the development of the blastocyst which theoretically has the potential for implantation and pregnancy decent shape.
Another option is the generation of animals that produce human gametes. Until now, it has been demonstrated that mice containing human ovarian xenotransplant can generate human oocytes (reproduction techniques 15;). human gametes could in theory also be made by a chimeric animal is produced by injecting human embryonic stem cells into animal blastocysts (18 reproductive techniques). The use of gametes produced by fertilization grafted or chimaeric animals could theoretically generate entity capable of implantation and pregnancy decent shape.
There is a proposal genetically alter somatic cell nucleus before transfer into enucleated donor oocyte in a way that would eliminate the potential for implantation of the resulting clone human embryos (reproduction techniques 16 and 17). This technique was recently demonstrated in a mouse model (). Briefly, the donor cells are genetically altered to disrupt the expression of genes important for the formation of a functional trophoblast. The resulting entity forming the inner cell mass, from which embryonic stem cells can be derived, but not being able to implant into the uterus. It has been argued that this technique, known as altered nuclear transfer, circumvents the ethical objection to using SCNT for the generation of human embryonic stem cells (;,;). To date, there are no reports that this technique has been successfully attempted in humans.
Gynogenetic and preimplantation embryos androgenetic only had a father or maternal genetic contribution, respectively (reproduction techniques 9 and 10). uniparental preimplantation embryos can be created by pronuclear transplantation. Androgenetic preimplantation embryos can also occur without experimental manipulations and result in what is known as a partial or complete hydatidiform mole depending on the morphological and genetic origin. Pathological distinguished hydatid mole can also biparental. A gene mutation, belongs to the family of proteins involved in the inflammatory response and programmed cell death, which causes recurrent hydatidiform moles in humans have been identified (). Although androgenetic and gynogenetic preimplantation embryo may develop to the blastocyst stage and implants, they are not able to build a decent pregnanciice.
parthenogenic preimplantation embryos (reproduction techniques 5) also uniparental because they only have a maternal genetic contribution. Although they can embed, they have limited the potential for subsequent development. In mice, parthenogenic embryos with the potential to develop into individuals who could feasibly be produced, but only after a large number of genetic manipulation (). In mice (;) and monkeys (), has shown that the preimplantation embryo parthenogenic can develop to the blastocyst stage and agree to the generation of embryonic stem cells. In humans, however, parthenotes unlikely to develop beyond the first few divisions, as centrioles contributed by human sperm centrosome required for the formation of functional ().
Most of the emerging technology are summarized in the results table entities that have the potential to implant and establish a viable pregnancy. Indeed, it is possible but not proven that they should be allowed to develop to term, will result in a live birth. It is therefore reasonable to conclude that if the technique is performed using human material, they can produce lifelike.
Some of the emerging technologies discussed above entities produce without the potential to form a viable pregnancy. From a purely biological perspective, this technique uses only human material would produce human blastocysts but not a viable pregnancy or live birth. If the potential to produce a live birth is to be a key element of the definition of a human embryo, then gynogenesis and androgenesis (reproduction techniques 9 and 10) will not be considered as a technique to produce human beings, even if only human material used.
The above discussion suggests that the potential for a new form of living things might indeed be a useful component of the definition of 'human embryo', as it allows the difference between emerging technologies that can lead to live births than those who do not.
number of technologies that appear in the table does not involve the contribution of chromosomal DNA by both sperm and oocytes or completion syngamy (2 reproduction techniques, 5-7, 9-11 and 16-17). However, some of these techniques, if done using human material, may have the potential to produce a live human births. Considering this, it is expected that human embryos would be created through the development process initiated using this technique. The inclusion of fertilization and syngamy as a necessary element in the definition of 'human embryo', will eliminate the emerging technologies that have the potential (even if the current theoretical) to produce the new man. Therefore, a prerequisite for fertilization and / or syngamy may not correspond to the biological definition of a human embryo.
Some of the emerging technologies theoretically result in an entity with which the human nuclear genome while the mitochondrial genome can be derived from other species (reproduction techniques 7). It is not known whether heteroplasmi mitochondria will cause developmental problems (). This is the unresolved aspects of SCNT, because maybe that cloned embryos will contain mitochondria from different sources, which is associated with heart transplant donors and also from the host-enucleated oocyte recipients.
Another possibility is the entity that contains cells of different species. Injection of mouse embryonic stem cell lines genetically altered into a blastocyst is used to generate transgenic mice and knockout mice (12 reproductive techniques). Because embryonic stem cell lines derived from different individuals to the blastocyst host, a chimaera produced. It is not clear whether this technique can be applied to the generation of interspecific chimaeras. Transplantation whole rat inner cell mass or inner cell mass cells of individual mice into mouse blastocysts did not produce a decent live births (). Therefore, the potential development of chimaeras made by injecting human embryonic stem cells into blastocysts from a different species (reproduction techniques 18) or by injecting embryonic stem cells into non-human human blastocysts (19 reproductive techniques;) unknown
Some of the techniques included in the table have the potential to produce an entity with DNA from more than one species. Any technique that can result in a live birth is likely to involve the formation ofembryo at some point early in the development process. Therefore, the biological definition of human embryo does not have to specifically exclude an entity created with DNA from the two species.
It has been previously noted, the potential for continued development should be a major consideration for any definition of 'embryo' (). The discussion presented in this paper fully supports this view. However, it is questionable whether it is possible to define 'human embryo' without making some reference to developments point in time.
Another approach to the development of the biological definition of 'human embryo' may be one that does not include references to specific time points of development, but in the context of the potential for continued development. The term 'human embryos' do not apply before the completion of the human oocyte fertilization with human sperm (ie syngamy), as this is when the new genome of a new individual is created. Before syngamy genome inherited maternal and paternal genomes exist as two separate.
The definition of 'human embryo' based syngamy excluding reproductive technology do not involve human oocytes fertilized with human sperm. Although some of these technologies may result in a live birth if applied to humans, it is clear from animal studies that others do not. From the perspective of biology, set a definitive time point in syngamy will include entities that do not have the potential to form a living human individual. It may be more appropriate to assess the potential of these entities to develop, or outside appearance, the primitive streak.
The above discussion shows that the definition of 'human embryo' may be separated into two components :. one for the early development resulting from the fertilization of the oocyte human with human sperm and the second for those produced by other means
The final consideration is whether the definition should refer to syngamy, which can not be visually confirmed until the initiation of mitotic first. Given that the purpose of this paper is to develop a biological definition of 'human embryo' may be to include a measurable event, such as the first mitotic division.
After considering the issues raised in previous discussions, the following biological definition of 'human embryo' proposed
a human embryo is a discrete entity arising both from :. and has not reached 8 weeks of development since the first mitotic division.
mitotic first when fertilization oocytes human with human sperm is complete or
another process that initiates conducted the development of biological entities to the nuclear genome of human or humans altered nuclear genome which have the potential to develop up with, or beyond, the stage in which the primitive streak appears,
this definition attempts to incorporate aspects of the observed developmental stage, the potential for development and the origin of DNA contribute to a new individual. It is recognized that this definition creates the possibility of an anomaly whereby an entity arising from the completion of the fertilization of the oocyte human with human sperm and, for whatever reason, do not have the potential for future development will be regarded as an embryo, while the entity identical artificially created will not have status of the embryo. However, the completion of the human oocyte fertilization with human sperm is enough to define the entity as human embryos irrespective of any potential, or lack thereof, for the future development.
After arriving in the biological definition of human embryo, it is instructive to apply the emerging technologies discussed earlier (Table).
emerging technologies and their status under the biological definition of human embryos
emerging technologies and their status under the biological definition of human embryos
naturally occurring process of early human development and emerging technology in reproductive science has been considered in this discussion paper. Deliberation is focused on biological processes and technology. On the basis of these facts, the biological definition of 'human embryo' was arrived at. The definition specifies that 'human embryo' term can not be applied before the completion syngamy, or after 8 weeks of development. biologicalal definition of 'human embryo' presented in this discussion paper also acknowledges that emerging reproductive technologies may one day provide an alternative to currently available reproductive techniques (such as in vitro fertilization, intra-cytoplasmic sperm injection). From a purely biological perspective, it is clear that the application of these technologies will generate new individuals who at some point in the development process will be a human embryo.
This definition does not specify how many human genetic content of an entity must have before it can be considered a human embryo. It is felt that this problem would be more effectively dealt with in the future as there are currently limited biological information. Until that moment, the 'humanity' of the genome should be considered on a case by case basis.
It is beyond the scope of this discussion paper to consider the consequences of the legal, ethical and moral that this emerging technology. However, it is expected that when the experts relevant consideration as they may use this paper as a source of information.
Debate article is an adaptation of Health and Medical Research Council (NHMRC) The National discussion paper 'embryo-human biological definition', which is available for download from. We thank James Catt, David Edgar, Martin Johnson, Anne McLaren, Martin Pera, Janet Rossant and Robert Seamark for their insightful comments on the original discussion paper. We also would like to thank Clive Morris and Greg Ash for their editorial comments. Peter Illingworth and Graeme Kay is a former member of the NHMRC Embryo Research Licensing Committee. The development of this definition is supported by the NHMRC embryo research licensing committee.
Oxford University Press is a department of the University of Oxford. It furthers the University goal of excellence in research, scholarship, and education by publishing worldwide
or
This PDF is available for Subscribers Only
For full access to this pdf, sign in to an existing account, or purchase an annual subscription.
Embryonic Development - Embryology
Embryo - Wikipedia
Photographs of human embryos at five stages of gestation ...
Learning about evolutionary history
File:Human embryo 8 weeks.JPG - Wikipedia
Embryo - Wikipedia
Human Embryo and Fetal Development - YouTube
Carnegie stage 23 - Embryology
Embryo experiments take 'baby steps' toward growing human organs ...
File:Human embryo 8 weeks 3.JPG - Wikimedia Commons
Early embryonic development who will be a man is one
Womb milk nourishes human embryo during first weeks of pregnancy ...
GettoknowMuhammad
But Is the Human Embryo a Person? | Catholic Lane
Is human embryo modification here? China's failed experiment ...
Embryonic Development - Embryology
New Studies: Frozen Embryos Not Always Necessary for IVF | Fortune
What is an Embryo? Scientists Warn Against Using Artificial ...
Embryo | definition of Embryo by Medical dictionary
China's failed gene-edited baby experiment proves we're not ready ...
Stages in human embryonic development Royalty Free Vector
Embryonic Development Images, Stock Photos & Vectors | Shutterstock
Biological entity of human embryo is a crucial bioethical issue
Human-Pig Hybrid Created in the Lab | National Geographic
Embryo | human and animal | Britannica
Embryo-like structures created from human stem cells
Animals' Embryonic Organizer Now Discovered in Human Cells | The ...
Genetically Modified Human Embryos: What You Need to Know | The ...
Hybrid zoo: Introducing pig–human embryos and a rat–mouse : Nature ...
Genome editing reveals role of gene important for human embryo ...
Embryonic Development Images, Stock Photos & Vectors | Shutterstock
Embryos have full human regeneration and regeneration could be key ...
Wait, What? The First Human-Monkey Hybrid Embryo Was Just Created ...
Human embryo CRISPR advances science but let's focus on ethics ...
Human fetus inside icon set Royalty Free Vector Image
Yolk Sac in Humans: Function, Definition & Measurement - Video ...
What is a human embryo? Answers, please, by 10 March ... - The IPKat
Database provides a rare peek at a human embryo's first weeks ...
Second CRISPR human embryo study shows there is a long way to go ...
Human embryo development - Curious
6 to 7 Week Old Human Embryo – Human Life International Shop
Fertilization and development review (article) | Khan Academy
How Researchers Cloned Human Embryos : Shots - Health News : NPR
U.S. panel gives yellow light to human embryo editing | Science | AAAS
Embryo Images Online- Credits
A first look at the earliest decisions that shape a human embryo
Why Can't We Experiment On Human Embryonic Stem Cells? - YouTube
Human Embryos, Human Beings: A Scientific and Philosophical ...
Embryonic Stem Cells | stemcells.nih.gov
Genome editing of human embryos broadens ethics discussions
Japan approves first human-animal embryo experiments
Posting Komentar
Posting Komentar