Embryonic stem cells and so-called iPS or induced pluripotent stem cells—skin cells reprogrammed into embryonic-like cells—have inherent molecular differences that demonstrate for the first time that the two cell types are clearly distinguishable from one another, researchers say. The data from the study conducted by scientists at the University of California, Los Angeles suggest that embryonic stem cells and the reprogrammed cells have overlapping, but still distinct, gene-expression signatures. The differing signatures were evident regardless of where the cell lines were generated, the methods by which they were derived, or the species from which they were isolated, the researchers say.

 

“We need to keep in mind that iPS cells are not perfectly similar to embryonic stem cells,” says Bill Lowry, a researcher with the Broad Stem Cell Research Center and a study author, which appears in the journal Cell Stem Cell. “We’re not sure what this means with regard to the biology of pluripotent stem cells. At this point our analyses comprise just an observation. It could be biologically irrelevant, or it could be manifested as an advantage or a disadvantage.”

 

The study was a collaboration between the labs of Lowry and UCLA researcher Kathrin Plath, who were among the first scientists and the first in California to reprogram human skin cells into iPS cells. The researchers performed microarray gene expression profiles on embryonic stem cells and iPS cells to measure the expression of thousands of genes at once, creating a global picture of cellular function.

 

The researchers say when the molecular signatures were compared, it was clear that certain genes were expressed differently in embryonic stem cells than they were in iPS cells. They then compared their data to that stored on a National Institutes of Health data base, submitted by laboratories worldwide. They analyzed that data to see if the genetic profiling conducted in other labs validated their findings, and again they found overlapping but distinct differences in gene expression, Lowry says.

 

“We can’t explain this, but it appears something is different about iPS cells and embryonic stem cells,” Lowry says. “And the differences are there, no matter whose lab the cells come from, whether they’re human or mouse cells or the method used to derive the iPS cells. Perhaps most importantly, many of these differences are shared amongst lines made in various ways.”