A University of California, San Francisco (USCF) team reports that miRNAs specific to embryonic stem cells promote the production of induced pluripotent stem (iPS) cells in mice. With the miRNAs, they utilized three instead of the usually used four transcription factors.
Previous methods typically used DNA that encodes four transcription factors: oct4, klf4, c-myc, and Sox2. The first three, however, are oncogenes. In the current study, the scientists wanted to eliminate the use of c-myc.
They induced pluripotency using a combination of infection and transfection. The infection involved introducing three viruses, each containing either oct4, klf4, or Sox2. The transfection involved a process in which miRNAs were mixed with a lipid, allowing them to pass through the cell membrane.
By labeling the fibroblast cells, they showed that the treated cells could be incorporated into a mouse embryo and that they went on to become every cell type in the adult animal, including germline cells that would produce the next generation of mice.
The miRNAs miR-291-3p, miR-294, and miR-295 increased the efficiency of reprogramming by oct4, sox2 and klf4 but not by these factors plus cMyc, the researchers say. C-myc binds the promoter of the miRNAs, suggesting that they are downstream effectors of c-myc during reprogramming. Unlike c-myc, however, the miRNAs induced a homogeneous population of iPS cell colonies.
The UCSF group is currently working on replacing all four transcription factors with miRNAs. They are also trying to understand the mechanism by which these small molecules are able to induce pluripotency. The team will also be looking to determine which miRNAs might be able to turn adult cells directly into particular adult cell types, bypassing the embryonic stem cell-like stage altogether.
Other Embryonic Stem Cell News
Supporters of hESC Research Ecstatic with President Obama’s Executive Order (Mar. 10, 2009)
Protein Complex that Determines Stem Cell Pluripotency Found (Mar. 3, 2009)
Pluripotent Stem Cells Created without Virus Vectors (Mar. 2, 2009)
ESC Research Advocates Pressure President Obama for Action (Feb. 20, 2009)
Testes Stem Cells Similar but Not as Pluripotent as ESCs (Jan. 6, 2009)