Tuesday, February 06, 2007

Erase and Rebuild to Program Stem Cells

My second Just Science post:

Biologists from Shanghai have discovered that cloned cells follow an "erase and rebuild" strategy to return to a state where they can begin dividing again. This isn't much of a surprise, since it's long been suspected that something like this happens. But it's nice to put a mechanism to things.
Huizhen Shang and colleagues report in a special stem cell issue of Cell Research that the developing (single) egg cells of mice erase many of the transcription factors and other modifications that control protein expression. The erasure strips away most of the programming done by the mouse's cells, leaving the cell in a "blank" state. (More technically, the chromatin, a mixture of DNA and proteins, factors are nearly all removed.) Then the egg cell gets rebuilt/reprogrammed after fertilization by sperm, and is ready to develop as a stem cell that forms a complete mouse.

In the early days of cloning (ten years ago), this reprogramming was done by electrocuting cells after a nucleus had been transferred into a denucleated oocyte. Nobody knew why this worked, but it did. With this new discovery, biologists can now determine how and what control factors are erased and reset.

Needless to say, but worth mentioning, is that this finding was not discovered in the U.S., due to the federal government's failure to support stem cell research.