Induced Pluripotent Stem Cells Remember Their Origins. (July 23, 2010)

Adult cells reprogrammed to resemble embryonic cells, i.e. induced pluripotent stem cells (iPS) have been shown in two recent studies to retain some signatures of the tissue from which they were derived.

Studying the ability of different stem cell types to make blood researchers at Children's Hospital, Boston found they could not get iPS cells made from fibroblasts to make blood cells. When they made iPS cells from blood cells, however, the reprogrammed cells made blood abundantly. On further study the researchers were able to show that each iPS cell line had a different pattern of DNA methylation. The iPS cells retain the methylation pattern typical of the cell of origin. Furthermore, different types of blood cells were shown to make slightly different iPS cells.

A second group working at the Harvard Stem Cell Institute found that they could identify the tissue of origin of each iPS cell line by examining the gene expression of freshly induced iPS cells. However, after 3 months, the gene-expression patterns in the various iPS cells became indistinguishable. The researchers suggest it may be that the expression of embryonic genes is strengthened as the cells grow in culture, gradually overwriting the cells' old gene-expression patterns, e,g, through epigenetic reversal.