Stem cells

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.