You never know what you are going to find in the trash. For a group of intrepid researchers at Michigan State University their discovery could lead to new ways of studying birth defects and other reproductive problems. Because what they found in what’s normally considered cellular trash was a new kind of stem cell.
The cell is called an induced extraembryonic endoderm stem (iXEN) cell. The team’s findings are reported in the journal Stem Cell Reports and here’s how lead author Tony Parenti described what they found:
“Other scientists may have seen these cells before, but they were considered to be defective, or cancer-like. Rather than ignore these cells that have been mislabeled as waste byproducts, we found gold in the garbage.”
Here’s the backstory to this discovery. For years researchers have considered embryonic stem cells as the “gold standard” for pluripotent cells, the kind that can be differentiated, or changed, into all kinds of cell in the body.
But studies in mice show that in addition to creating these pluripotent stem cells, the mouse embryo also produces extraembryonic endoderm or XEN cells. For a long time it was believed the gene expression of XEN cells affected the pluripotent stem cells, but the XEN cells were usually thought to be cancer-like, something that occurred as a byproduct of the developing embryo.
Searching through the trash
And that’s how things stayed until the research team at MSU noticed a bunch of XEN-like cells showing up every time they created induced pluripotent stem (iPS) cells – a kind of man-made equivalent of embryonic cells with the ability to turn into any other kind of cell but derived in a different way, reprogrammed from adult cells.
So they set out to see how important these, what they called induced or iXEN, cells were to the development of iPS cells. The researchers took adult mouse cells and reprogrammed them into iPS cells and noticed colonies of iXEN cells in these cultures.
The first goal was to make sure these iXEN cells weren’t cancer-causing, as many researchers believed. This took six months but at the end of it not only were they able to demonstrate that the cells aren’t cancer-causing in a cell culture dish, but that they are a new type of stem cell.
Next step was to see how important endodermal genes are in the formation of iXEN cells. They found that decreasing endodermal gene expression led to a two-fold decrease in the number of iXEN cells and a significant increase in the number of iPS cells.
Competitors not collaborators
They concluded that the parallel pathways that generate pluripotent and XEN cells are in competition with each other and not in support of each other during reprogramming. By suppressing one they were able to boost the other. To their delight they had stumbled on a more efficient way of creating iPS cells.
While the discovery of a new kind of stem cell is always exciting there’s a catch to this; we still don’t know if XEN cells are found in humans. But this discovery gives the researchers additional tools to try and find the answer to that question.
Amy Ralston, a co-author of the study, said in a news release:
“It’s a missing tool that we don’t have yet. It’s true that XEN cells have characteristics that pluripotent stem cells do not have. Because of those traits, iXEN cells can shed light on reproductive diseases. If we can continue to unlock the secrets of iXEN cells, we may be able to improve induced pluripotent stem cell quality and lay the groundwork for future research on tissues that protect and nourish the human embryo.”
Normally the discovery of anything new, particularly when it over turns a long-held belief, is met with a degree of healthy skepticism at first. In science that’s a good thing. We all remember the eager way that STAP stem cells were hailed by many as a new way to create pluripotent stem cells until the research was discredited. But so far the Twitterverse and media outlets seems to share in the excitement about this discovery.