Properties[ edit ] The classical definition of a stem cell requires that it possesses two properties: In the strictest sense, this requires stem cells to be either totipotent or pluripotent —to be able to give rise to any mature cell type, although multipotent or unipotent progenitor cells are sometimes referred to as stem cells. Apart from this it is said that stem cell function is regulated in a feed back mechanism. Self-renewal[ edit ] Two mechanisms exist to ensure that a stem cell population is maintained:
Advanced Search Abstract The use of human embryos for research on embryonic stem ES cells is currently high on the ethical and political agenda in many countries.
Despite the potential benefit of using human ES cells in the treatment of disease, their use remains controversial because of their derivation from early embryos. There are several reasons for this.
To date, most embryos used for the establishment of hES cell lines have been spare embryos from IVF, but the creation of embryos specifically for deriving hES cells is also under discussion.
The UK has been the first to pass a law governing the use of human embryos for stem cell research. The European Science Foundation has established a committee to make an inventory of the positions taken by governments of countries within Europe on this issue European Science Foundation, In order to discuss the moral aspects of the isolation and use of hES cells, which is the aim of the present article, it is first essential to understand exactly what these cells are, where they come from, their intended applications and to define the ethical questions to be addressed.
What are embryonic stem cells? Broadly speaking, two types of stem cell can be distinguished: In humans, hEG cells were first established in culture inshortly after the first hES cells, from tissue derived from an aborted fetus Shamblott et al.
In the adult individual, a variety of tissues have also been found to harbour stem cell populations. Examples include the brain, skeletal muscle, bone marrow and umbilical cord blood, although the heart, by contrast, contains no stem cells after birth reviewed in McKay ; Fuchs and Segre, ; Watt and Hogan, ; Weissman et al.
These adult stem cells have generally been regarded as having the capacity to form only the cell types of the organ in which they are found, but recently they have been shown to exhibit an unexpected versatility Ferrari et al.
Evidence is strongest in animal experiments, but is increasing in humans, that adult stem cells originating in one germ layer can form a variety of other derivatives of the same germ layer e. To what extent transdifferentiated cells are immortal or acquire appropriate function in host tissue remains largely to be established but advances in this area are rapid, particularly for multipotent adult progenitor cells MAPCs of bone marrow Reyes and Verfaillie, Answers to these questions with respect to MAPCs, in particular whether they represent biological equivalents to hES and can likewise be expanded indefinitely whilst retaining their differentiation potential, are currently being addressed Jiang et al.
For other adult stem cell types, such as those from brain, skin or intestine Fuchs and Segre,this may remain unclear for the immediate future. Examples in fundamental research on early human development are the causes of early pregnancy loss, aspects of embryonic ageing and the failure of pregnancy in older women where genetic defects in the oocyte appear to be important.
A second category might be toxicology, more specifically research on possible toxic effects of new drugs on early embryonic cells which are often more sensitive than adult cells drug screening.
The most important potential use of hES cells is, however, clinically in transplantation medicine, where they could be used to develop cell replacement therapies. It is unfortunate that sensational treatment in the media, which implied the generation of whole organs from hES cells, initially left this impression so that the more realistic view emerging is already a disappointment to some patient groups.
There are, at least in theory, various sources of hES cells. In most cases to date, these have been spare IVF embryos, although IVF embryos have been specifically created for the purpose of stem cell isolation Lanzendorf et al.
This option is purported to be the optimal medical use of hES technology since the nuclear DNA of the cells is derived from a somatic cell of a patient to receive the transplant, reducing the chances of tissue rejection see Barrientos et al.
It is of note that the oocyte in this case is not fertilized, but receives maternal and paternal genomes from the donor cell nucleus. Since by some definitions an embryo is the result of fertilization of an oocyte by sperm, there is no absolute consensus that nuclear transfer gives rise to an embryo see below.
Growth of the cell lines over extended periods and in some cases under defined conditions Xu et al.Stem cell research is one of the most fascinating areas of contemporary biology, but, as with many expanding fields of scientific inquiry, research on stem cells raises scientific questions as rapidly as it generates new discoveries.
embryonic stem cells are derived from the inner cell mass of the blastocyst, or early stage embryo that is approximately four to five days old in humans and consists of 50– cells.
A discussion of the pros and cons, background, and latest developments in the ethical debate over embryonic stem cell research.
Pros and Cons of Stem Cell Research. The UK allows embryonic stem cell cloning. There's a lot of fiction surrounding stem-cell facts. To separate one from the other, WebMD has consulted experts including Mahendra Rao, MD, PhD, director of the Center for Regenerative Medicine.
These cells are reducing the need for human embryos in research and opening up exciting new possibilities for stem cell therapies. Both human embryonic stem (hES) cells and induced pluripotent stem (iPS) cells are pluripotent: they can become any type of cell in the body.
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Embryonic Stem Cell Research. Pluripotent stem cell lines can be derived from the inner cell mass of the 5- to 7-d-old blastocyst. However, human embryonic stem cell (hESC) research is ethically and politically controversial because it involves the destruction of human embryos.