Understanding Differentiation In Human Embryonic Stem Cells

Researchers know very little about how human embryonic stem cells (hESC) self-renew. To fully understand these cells' self renewal capacity and pluripotency, and their regulation, it is necessary to efficiently generate genetically modified cells and analyze the consequences of elevated and reduced expression of genes.

The researchers used "knockdown" technology to reduce the expression of oct4, a gene known to be necessary for self renewal of mouse and human embryonic stem cells. As seen in work done with mouse cells by knockdown and other genetic means, they showed that reducing the amount of oct4 in human ES cells induced differentiation. The researchers then used a plasmid vector to transiently increase levels of oct4 in hESC.

This also resulted in differentiation as expected, but with differentiation patterns similar to those seen with the knockdown. This was an unexpected result, because when expression of oct4 is up-regulated in mouse ES cells, they differentiate into a different type of cell than if the expression of oct4 is down-regulated.

The research team, led by the University of Minnesota's Meri Firpo, Ph.D., included gene therapy researchers at Los Angeles Children's Hospital, and developmental biologists at the University of Michigan.

"This suggests a key difference in the regulation of early development between mouse and human embryos" Firpo said. "While animal models are clearly important, this research shows that scientists need human models to truly understand what happens in early human development."

The research appears in the November 2007 issue of Experimental Biology and Medicine.