FAQ

What are "Embryonic Stem (ES) Cells"?
Embryonic stem cells have several characteristics: they are undifferentiated, pluripotent and can be cultivated to an unlimited extent ("self-renewal").

What is "Totipotency"?
Totipotency is the capability of cells to create a complete new organism, including all tissues and a placenta. Only the so called "blastomeres" up to the very early 8-cell-stage of an embryo seem to have totipotency.

What is "Pluripotency"?
Pluripotency is the capability of stem cells to develop into 200 different cell types, but having lost the capability to create a placenta. Embryonic stem cells are pluripotent from the 8 cell-stage onwards.

What is "Multipotency"?
Multipotency is the capability of stem cells to develop into a limited range of tissues. A blood stem cell for example has the capability to develop into any type of blood cell (erythrocyte, granulocyte, monocyte, etc.), but does not have the ability to form different cells types, for example neurons, which originate from a different germ layer. Adult stem cells seem to be multipotent.

What are "Undifferentiated ES cells"?
Undifferentiated ES cells can be cultivated in vitro indefinitely and produce millions of identical offspring.

What are "Adult (=committed, =somatic, =tissue-specific) Stem Cells"?
Adult stem cells or committed, somatic or tissue-specific stem cells are multipotent cells and can create a limited range of tissues. Adult stem cells play an important role in the replacement of old and damaged tissues in the mammalian body.

What is "Genomics"?
The term "Genomics" refers to the analysis of the genome of an organism. The "genome" is the complete set of "genes" that a cell contains. Genetic information of all organisms is written down in the "code of life", DNA (Desoxyribo-Nucleic-Acid) of certain length and order. A "gene" is a unit of DNA that encodes for a specific molecule of RNA (Ribo-Nucleic-Acid). This RNA molecule is "translated" into a specific protein, which again has a defined function in a cell. In 2001 the "Human Genome Project" identified the complete sequence of the human genome and in 2003 the same was done for the mouse genome. The sequencing data refer to "structural genomics" whereas the function of a gene is identified by means of "functional genomics":

What is "Functional Genomics" ?
Functional genomics refers to the analysis of gene functions by means of ""high throughput" methods, in combination with data analysis on a large scale. Functional genomics extends the possibilities of biological investigation from studying only single genes to studying all genes of a cell at the same time in a systematic manner.
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What is "RNA interfernce (RNAi)"?
RNAi is an evolutionarily conserved mechanism found in almost all higher organisms and believed to be an antiviral defence mechanism. In a cell, genes are first "transcribed" into a messenger RNA (mRNA) copy. Specialised structures in the cell (so-called "ribosomes") then "translate" this mRNA molecule into a protein. The process of transcription and translation of a gene is called "expression". RNAi reduces the expression of a gene before it is translated into a protein - as a result, the amount of the affected protein in the cell is reduced. Short RNA molecules of about 20 basepairs bind to complementary mRNA sequences and lead to their destruction (small interfering RNA, siRNA). By using the new technique of esiRNA, siRNA is prepared by the bacterial enzyme endoribonuclease (endoribonuclease prepared short interfering RNA, esiRNA).

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What are "DNA Microarrays"?
DNA Microarrays such as Affymetrix Gene Chips play an essential role in functional genomics. Such a chip contains thousands of spots consisting of short stretches of DNA. Each spot is specific for one particular gene. RNA is isolated from a cell, labelled with a fluorescent molecule, and then added to the chip. RNA molecules can bind to their specific counterpart present on the chip. The chip is then read by a high resolution scanner, and the fluorescence intensity of a spot is used to determine how strongly the gene was expressed in the cell. By comparing RNA prepared from cells in different stages of development, we can identify genes which are active under certain conditions.

What is "Overexpression of genes" ?
By introducing a suitably designed stretch of DNA containing a gene of interest into a cell, this gene (and therefore its products) can be produced in very high amounts (also called overexpression). Changes in the properties, morphology or behaviour of the cell can offer evidence about the function of the overexpressed gene.

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What are "Reporter Genes"?
ES cells can be engineered for specific tasks by introducing novel DNA fragments designed to serve a specific purpose. For example, "reporter genes" can make cells fluorescent in UV light if the particular gene is expressed, thus allow tracking gene activity in living cells. A commonly used example in cardiac studies is the introduction of a DNA fragment containing the fluorescent dye EGFP (enhanced green fluorescent protein, originally found in the jellyfish Aequoria victoria) together with the gene for the alpha-actinin gene, a protein that is exclusively expressed in cardiomyocytes. Green fluorescent cells express alpha-actinin and can be identified as cardiomyocytes, respectively their progenitors.

What is a "BAC (Bacterial Artificial Chromosome)"?
A BAC is a so called "vector"(comparable to a "plasmid") able to accomodate big stretches of DNA (>100 kb). BACs can be modified in such a way that the control sequence of a gene (mainly the "promotor") will stay as it is, but the "coding sequence", i.e. the part that is translated into a protein, is replaced by a reporter gene. This reporter gene can be a gene for a fluorescent protein (see above). Additionally, one can insert so-called "resistance genes" into the BAC. These are genes which make a cell immune against an antibiotic.

The newly constructed BACs are afterwards inserted into ES cells. By applying the antibiotic to the culture, only those cells survive which carry the BAC. This can be called selective cultivation.

What is "Knockout Technology"?
Knockouts are commonly performed in mice. A "knockout mouse" is a mouse in which a gene is specifically inactivated ("knocked out") by genetical manipulation.

At first undifferentiated ES cells from a mouse blastocyst and cultivated in vitro. Next vectors such as BACs with the "knocked-out" gene are transferred into the ES cells and replace the original gene present in the cells. These ES cells are now intoduced into a second blastocyst, and this blastocyst is implanted in a "pseudo-pregnant" mouse. The developing embryos contain cells from the mother and from our enginerred ES cells. This is what we call "chimeric". After the chimeric embryos develop to an adult stage, we breed them with "wildtype mice" and obtain "heterozygous" mice which are then re-crossed again to obtain "homozygous" animals, i.e. mice that have only the genetic material of our implanted ES cells with the "knocked-out" gene. In these animals we can study the results of the "knock-out".

What is "Knockout Technology"?
Here we use the same technique as in knockout-technology, the only difference being that that no gene of interest is inactivated, but a gene of interest is introduced (see below). In the knockin animals we can then study the function of the overexpressed gene.

   

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