Researchers have demonstrated how embryonic stem cells are converted into tissue-specific cells.
Researchers at the Hebrew University of Jerusalem have successfully revealed this process graphically and provided the answer to the long-standing question as to whether the stem cells achieve their development through selective activation or selective repression of genes.
The team of researchers including Dr. Eran Meshorer of the Department of Genetics at the Silberman Institute of Life Sciences at the Hebrew University of Jerusalem has revealed that the embryonic stem (ES) cells express a major part of their genome "promiscuously."
This liberal expression includes lineage-specific and tissue-specific genes, non-coding regions of the genome that are normally "silent," and repetitive sequences in the genome, comprising the majority of the mammalian genome but are also normally not expressed.
At the time of differentiation into specific cell tissue-types, ES cells undergo global genetic silencing. But till this time, the ES cells maintain an open and active genome. This may hold the key to their success, as this flexibility allows them to maintain their capacity to become any cell type. However, this ability is lost once silencing, or genetic repression occurs.
This implies that the ES cells stand at the ready until the "last minute," prepared to engage in selective activation into specific cells, holding "in abeyance" their ability to become any kind of cells at the point and time required.
In order to reveal this process, the researchers created the first full-mouse genomic platform of DNA microarrays. Microarrays are glass-based chips that allow simultaneous detection of thousands of genes. The microarrays used in the study were not confined to specific genes only but spanned the entire genome.
The researchers required hundreds of such microarrays for this study to cover the entire genome in different time points during stem cell differentiation. And by observing these sequences they could ascertain exactly how and at what point the stem cells developed into specific tissue cells and when the silencing occurs.