Yu, Thomson, and all, from Wisconsin published their paper on reprogrammed induced Pluripotent Stem (iPS) cells from adult cells online in Science Express online, yesterday, just after the Yamanaka/Takahashi team from Japan published theirs in the journal, Cell. (The Thomson paper was not scheduled to go live online until the 22nd.)
As discussed on this blog, yesterday, Yamanaka’s group built on their earlier research published in 2006 and 2007, using mouse fibroblasts to prove that four genes, Oct4, Sox2, c-myc, and Klf4, could reprogram those cells to a state that resembled embryonic stem cells in all tests that they tried. Then, they used fibroblasts from commercially available samples from 1) a skin biopsy taken from the face of a 36 year-old Caucasian woman, 2) synovial cells (joint lining) from a 69 year old Caucasian male, and 3) neonate foreskin skin fibroblasts.
(This last is a common source of skin fibroblasts, with easily and ethically accessed skin tissue, collected at the circumcision of newborn boys.)
The Thomson team did not begin the basic research using mouse cells and did not simply go forward using the genes from the earlier experiments on mouse cells. Instead, they started at the beginning, using human Embryonic Stem Cells (hESC) that had been directed to become a special type of white blood cell, CD45+. This type of cell can be manipulated to demonstrate whether they had the functioning gene, Oct4 (a definite marker that is used to prove whether or not a cell is a hESC), by growing them in the presence of gentamycin, an antibacterial.
By adding some genes and removing others, the team determined that they had, “identified a core set of 4 genes, OCT4, SOX2, NANOG, and LIN28, that were capable of reprogramming human ES cell-derived somatic cells.” They also discovered that the cells could be reprogrammed into embryonic-like cells without Nanog, but that Nanog made it possible to recover more reprogrammed cells.
(From the text accompanying Fig.1: “In three independent experiments using different preparations of
mesenchymal cells, individual removal of either OCT4 or SOX2 from reprogramming combinations eliminated the appearance of reprogrammed clones, whereas the individual removal of either NANOG or LIN28 reduced the number of reprogrammed clones, but did not eliminate such clones entirely.”)
Next, they tested this combination of genes in a commercially available, genetically modified cell culture, IMR90 fetal fibroblasts. (These cells were cultured from a little girl aborted at 16 weeks gestation. ) These cells are fetal cells, not adult cells, and they were chosen because they have been studied and the genome is well known. They do not grow well in the fluids and conditions that encourage cultures of hESCs and the researchers could identify them by the way that they look.
Next, in order to prove that the genes could reprogram “adult cells,” the team used fibroblast cultures from foreskins to produce 4 different cultures of reprogrammed induced Pluripotent Stem Cells.
The authors conclude,
“The human iPS cells described here meet the defining criteria we originally proposed for human ES cells, with the significant exception that the iPS cells are not derived from embryos. Similar to human ES cells, human iPS cells should prove useful for studying the development and function of human tissues, for discovering and testing new drugs, and for transplantation medicine.”
Edited typos 11/21/07 17:30 PM (That could be the next neuroscience break through: why don’t we see our typos until later?)