Stem Cells: Basic Concepts
Definition of stem cells: those cells with the ability to simultaneously self-renewal (ie, produce more stem cells) and cause daughter cells committed to specific development paths, which finally become specialized cell types differentiation.
In the context of the present investigation is to obtain stem cells to remain as such in laboratory culture, and that under certain stimuli can lead to different cell populations.
The zygote (fertilized egg) is a totipotent cell, capable of giving rise to the whole organism. During the first division the embryo is a compact sphere (morula), in which all cells are totipotent, and indeed this is reflected naturally in monozygotic twins. A few days after starting a first specialization, so as to produce a blastocyst, with a surface layer that give rise to the trophoblast, resulting in the placenta, and a cavity almost “hollow” (filled with fluid), which is the inner cell mass (ICM).
The cells of this m.c.i. are pluritotentes, because although by themselves can not give rise to the entire fetus (need the trophoblast) are the source of all tissues and cell types of the adult.
We must clarify one point: although the cells of the blastocyst inner cell mass are pluripotent, are not themselves within the embryo stem cells because they do not remain indefinitely as such in vivo, but differ on the various cell types intrauterine phase. What happens is that when removed from the embryo and cultured in vitro under certain conditions, cells become “immortal” endowed with these two properties we talked about: self-renewal and pluripotency.
Getting in mouse embryonic stem cells: from the early 80′s. Currently, in almost any breed of mouse blastomeres can be separated mci from blastocysts and grow them so that the resulting cells (stem cells or stem, stem cells) have two remarkable properties: pluripotency and ability to contribute to the germ line:
Pluripotency, stem cells can differentiate in vivo and in vitro in a variety of cell types.
In vivo that occurs when multipotent stem cells to incorporate into blastocysts can give rise to any tissue or organ
In vitro may also contribute, with the right signals to different cell lines of the three germ layers (ecto-, meso-and endoderm). This is the field where more is currently being investigated for their relevance to therapeutic cloning, as we shall see.
Contribution to the germ line: The mouse embryonic stem cells can contribute to the germ line of chimeric mice. If injected stem cells cultured from a strain of mouse within a normal embryo (blastocyst) of another race, such stem cells can give rise to any type of adult tissue. What is interesting here is that in some cases serve as a source for germ cells (sperm or eggs). These mice in which there are tissues from two distinct races are called chimeras, and some chimeras reproductive cells derived from stem cells introduced into the blastocyst, so that their genetic makeup can be distinguished from somatic cells.
If we manipulate stem cells by genetic engineering, and transfer to a blastocyst, we can obtain chimeric mice in which part of the tissues are genetically engineered. If manipulated stem cells contribute to the germline, the modified genetic trait in the chimeric mouse is transmitted to offspring, becoming then a line of transgenic mice. Transgenic mice, including so-called KO (Noquedados genetically, ie, a mutant gene inserted by homologous recomibinación) are now an invaluable tool in biology and modeling human diseases.
Other stem cells:
Germline stem cells (EG) were isolated from fetuses from the germinal ridge, which is producing the differentiation of the germ line.
Adult stem cells (AS): The outstanding example is the hematopoietic stem cell (HSC), which generates all types of blood cells and immune system, and resides in the bone marrow (although in the fetal stage is in hígago and spleen).
credit to: Enrique Iáñez