Chimera may bring things like lizards or Sharktopus To sanity, but you won’t see any of the people walking by your TV (or strolling on the beach).
Not all chimeras have to look like they jumped out of a sci-fi horror movie. There is now a way to culture human stem cells at an earlier stage than ever before, which means that these cells have a much better chance of transforming into any organ they integrate with, human or animal. Successful integration can create complete chimeric organs. It may one day be grown in a laboratory and passed from animals to humans, or from humans to other humans.
A breakthrough that could end up removing people from transplant waiting lists in the future was made by a team of researchers from the Weizmann Institute of Science in Israel. It will be a while before anyone has ever had pig liver, but the team has managed to do what was previously thought impossible. Capturing human cells at such an early or “naive” stage means that they have not yet differentiated and have the potential to transform into almost anything.
“The state of stem cells can be modified by specific exogenous factors that support the naive state of pluripotency,” the researchers said in a study recently published in Cell Stem Cell.
Imagination began turning to science in 2013 when the same researchers showed that they could inject human cells into mouse embryos, and that those cells had already fused into the embryos. The cells used at that time were already at an early stage. This is not quite as easy as it sounds, as stem cells can be unstable and often refuse to fuse. Few actually reach the point where they become a part of any organ or organism into which they are placed. Now, Wiseman’s team has been able to culture human cells at an early stage, opening up even more possibilities.
The pluripotent stem cells can multiply and form the three main cell layers of the embryo which will later grow in every part of the body. Although they are slightly more limited than full-potent stem cells, which have not even begun to differentiate into those layers, the more naive the pluripotent cells are, the easier it is to manipulate them. Naive pluripotent stem cells also have epigenetic properties – controlled by genetic factors other than DNA – that enable them to undergo transformations that stem cells at later stages cannot. They also express genes in a pattern that distinguishes them from more mature pluripotent cells.
Part of the reason for the team’s success with this transfer is the increased stability of the cell. This made them five times more likely to integrate into what would become a chimeric organ or embryo, but only after several procedures to stabilize it. The researchers needed to block two signaling pathways, each of which is a series of chemical reactions within cells that control what cells do, such as how they divide. This, combined with the mutation of a gene strongly related to stability, helped the cells to integrate wherever they were transplanted. However, one hurdle remained – evolution.
Future experiments should take into account the differences between human evolution and the evolution of any other animal used to produce additional cells or organ. At least now you can be sure that there’s no way you’re going to run into any lizard men.