Stem cells
A stem cell is an undifferentiated cell is characterized by its ability to generate specialized cells in differentiating and its ability to grow almost infinitely to the same (self), particularly in culture.

A cell is said to stem cell (or undifferentiated cell) in two conditions:
1. It can provide specialized cell by cell differentiation and
2. It can virtually be renewed indefinitely.

They are present in the embryonic stage and in the adult organism, but they are much more rare in the adult organism (such as hematopoietic stem cells continuously regenerate blood cells, intestinal stem cells, neural stem cells in regions specific regions of the brain (hippocampus, an area subventriculaire)). In general, stem cells are present in all living multicellular. They play a very important role in the development of organisms and in maintaining them.

The most undifferentiated cell is the zygote or fertilized egg, since the egg will produce all the cells of an organism. We talk about stem cells in animals, but the plant meristems are also formed. In a more comprehensive, all multicellular organisms have stem cells.

Stem cells of animals and in particular human stem cells are the subject of much current research, including medicine to regenerate tissues or create any piece of tissue and organs is the goal of therapy Cell. The origin of stem cells used in research also raises ethical issues: indeed, they come mostly from embryos, although it has recently discovered the possibility of using other sources such as blood cells umbilical cord, or stem cells from adipose tissue. When they allow research on stem cells, the legal limit it to cells from spare embryos from procedures for medically assisted procreation (PMA), prohibiting in particular the creation of embryos solely for the purpose of search. Moreover, given the potential benefits that they seemed to present, trials of therapeutic cloning have been developed to control the production in large numbers.

Stem cell culture

Origin of stem cells
For medical or scientific research, human stem cells (and more generally mammalian) may also be classified in relation to their origin: embryonic, fetal or adult.

Embryonic Stem Cells
Also called ES cells are pluripotent stem cells present in the embryo shortly after fertilization until the stage of blastocyst development said they are still the inner cell mass (the other cells of the blastocyst are the cells of the trophectoderm).

These cells are the source of all tissues of the adult organism and are pluripotent. They can be isolated and cultured in vitro in the undifferentiated state. In terms of specific cultures (on suspension growth ...), individuals can direct their differentiation to a given cell type (neurons, melanocytes, muscle cells, blood cells ...).

Embryonic stem cells were isolated and grown in mice from the early 1980s and helped develop the technique of gene invalidation by homologous recombination (or knock-out) which, after reintroduction of these cells mutated into a recipient embryo and crossings, to obtain mice homozygous for a mutation in a gene.

They are in practice taken from cells of the internal mass of the blastocyst (an embryo that is less than 150 cells), which requires the destruction of the embryo. They can be obtained from frozen embryos from in vitro fertilization or by cloning (by transferring the nucleus of a cell into an egg).

These cells could enable the development of a cell therapy for many degenerative diseases (eg regeneration of injured dopamine neurons in Parkinson's disease after reintroduction into the brain, repair of damaged heart muscle tissue after a heart attack ... ).

Research on embryonic stem cells are currently not very advanced, mainly because of ethical and legal.

Fetal stem cells
A fetal stem cell is a type of multipotent stem cells of fetal origin. They can be harvested from fetuses from a voluntary interruption of pregnancy. Fetal stem cells have the characteristic of being directed to a particular cell type.

Adult Stem Cells
Adult stem cells are undifferentiated cells that are found in tissues that are composed mainly of differentiated cells in most adult tissues and organs. These are generally multipotent cells. They are capable of giving rise to different cell lines of a given tissue. They are the basis of a natural renewal and tissue repair in response to injury.

They are already used in the processing of more than one hundred diseases. They are called "somatic" as opposed to germ cells, and can be found not only among adults but also among children and even in the umbilical cord.

Interest in Research
  1. Molecular Study on the human embryo in its early stage of development.
  2. Interest of such cell lines to study the process of biological development from its initial phase and see how far back and the defects that cause chromosomal abnormalities like Down syndrome (or trisomy 21).
  3. These cells, in some of its features (speed of division, biochemical reactions, expressions of genes), closely akin to precancerous cells. They are thus by their unstable state, an interesting model to address a situation in which a cell can switch to the cancerous condition, in conjunction with genomic research.
  4. The research on human pluripotent stem cells may also induce changes in the way of drug development and to test them in a safe and healthy by testing for varieties cellular many more.
Therapeutic application
1. Pluripotent stem cells have the potential for practitioners unlimited source of tissues or specific cells. It hopes to expand the scope for interventions cell therapy for diseases such as Alzheimer's, Parkinson's disease of the bone marrow, heart attack or stroke, burns, diabetes, osteoarthritis or rheumatoid arthritis.
2. It is hoped that these cells can replace cells destroyed (ischemia, irradiation, self, chemotherapy, ...) or overcome cellular functional deficits (Parkinson enzymopathies, etc.)..
3. Stem cells could also contribute to the development of tissue engineering. They have proven their ability to produce four types of muscle fibers exist and could be located on the substrate or tissue on smooth muscle of blood vessels of the heart.
4. Hopes for gene therapy are numerous:
  • first applied to abnormal tissues or organs due to the presence of a gene mutated in individuals or young adults.
  • second consists in the correction, by somatic gene therapy, an abnormal gene carried by the parents and sent to the fertilized egg. The aim would be that the child does not have the disease resulting from abnormal gene from his parents.
  • third is to correct an abnormal gene cloned intra-couple, ie to obtain a cure through cloning: cloning from oocytes of women through nuclear transfer cell, corrected and from a couple of the blastocyst. This solution is the only way to eliminate and certainly the gene abnormality, while creating an egg reconstituted from the genomes of both parents. It is both a cloning and germ line therapy, but within the couple. This means that embryos used to produce the cells will not be sacrificed but will, instead, his chances of leading to the birth of a child free from the anomaly.


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