Human embryonic stem cells (HESC) are the cells which can transform itself into any other type of cells. This transforming ability has offered hope of producing human organs needed to replace when damaged due to injury or chronic disease.

Till now the exact mechanism by which this occurs was unknown . But now, Hebrew University researchers and colleagues abroad have discovered the exact mechanism by which this occurs. After knowing the mechanism a new question arises that whether stem cells develop through selective activation or selective repression of genes.

The collaborative research group including, Dr. Eran Meshorer of the genetics department at HU’s Silberman Institute of Life Sciences and scientists from US National Institutes of Health, the Affymetrix company in California and the Hospital for Sick Children in Toronto reveal that HESC express large proportions of their genome “promiscuously. This permissive expression includes lineage specific and tissue specific genes. While the non coding regions of the genome and repetitive sequences in the genome which comprises the majority of the mammalian genome remains silent.

They also revealed that when HESC s differentiate into specific tissue types, they undergo global genetic silencing. But until this occurs, the cells maintain an open and active genome. Thus by maintaining this flexibility they maintain their capacity to become any cell type. It can also be said that stem cells stand, at a ready until ‘the last minute’ they prepared to engage in selective activation into specific cells.

Once they are in silencing or genetic repression mode this ability is gone. To know how this occurs the researchers created full mouse genomic platform of DNA microarrays which are mainly glass based chips that allow simultaneous detection of thousand of genes. These microarrays were not confined to specific genes but spanned to entire genome. To cover entire genome at different points during stem cell differentiation hundreds of such micro arrays were required. After observing these sequences the researchers were able to establish exactly how and at what point stem cells develop into specific tissue cells and when the silencing occurs.

Source: health & scitech