One of the things I like about my job is that there's always the opportunity to learn new things. Today I learned about episomes. Not being an actual geneticist & all, it was a novel term to me. An episome is defined as:
a portion of genetic material that can exist independent of the main body of genetic material (called the chromosome) at some times, while at other times is able to integrate into the chromosome.
By that definition, transposons and viruses would both be episomes, while bacterial plasmids aren't, because they don't insert themselves into the main bacterial chromosome.
I learned about them as a result of discovering that Bad Science Reporting is always out there somewhere, courtesy of my blogging buddy Aimee, who sent me this link to a report on how scientists have cleared a path to the fountain of youth. Yes, really.
It's an article about some rather interesting research into the possibility of reprogramming adult cells so that they return to a pluripotent stem cell state. (You can read the original paper here at PLoS One: the genetics is a bit technical but the intro & discussion are reasonably straightforward.) Reprogramming somatic cells often uses viruses, which can be problematic if the viral DNA inserts into the 'wrong' place in the recipient cells' genomes, but if transfection agents aren't used then conversion of body cells to stem cells tends to have a very low success rate: the authors of the PLoS One paper give a figure of 0.001% to 0.5% (Park, Huo, Peters, Talbot, Verma, Zimmerlin, Kaplan & Zambidis, 2012).
However, the researchers report figures of around 50%, which is quite something. They did it using cord blood (ie umbilical cord blood), where the cells were 'lineage committed' ie they had already differentiated from the pluripotent state, and tweaking gene expression in those cells using 'episomal nucleofection' to carry a set of four key genes into the cells' nuclei. (The earlier you catch cells post-differentiation, the easier it apparently is to nudge them back to pluripotency: 'developmentally immature' cells (Park et al., 2012) will revert at a higher rate than fully differentiated adult cells.)
So, preliminary proof of concept, but a long way from inducing adult tissue cells to re-enter a stem cell state.
Unfortunately, the writer of the article Aimee pointed me at seems to have been a little overenthusiastic in their reporting:
an efficient and totally safe method to turn adult blood cells [back to their embryonic state]. The discovery could be the key to cure the incurable - from heart attacks to severed spinal cord to cancer - and open the door, some day, to eternal youth.
For some reason the article talks of obtaining 'adult blood cells' from a patient's spinal cord, when the original paper talks of cord blood from a cord blood bank (ie we are talking umbilical cords). It also mentions plasmids, when the paper talks of episomes. (I guess that one's less obvious as I thought 'plasmids' on first reading & had to look up episomes for myself!).
As for 'totally safe' - hmmm, that one I would want to hear more about. Plasmids don't integrate into host DNA, but episomes do - so the potential is still there for disruption of functional genes. But the phrase that nearly made me cough tea over the keyboard was this:
the cultivated cells magically turned to embryonic stem cells.
No, no, no! The researchers are able to describe the mechanism. They are pretty clear on what has happened. This is SCIENCE, not some magical intervention!
I will leave my readers to debate whether this final vision of a brave new world is necessarily one to look forward to:
Hypothetically, if you're able to perpetually fix any part of your body, there's no reason you wouldn't be able to live as long as you wanted.
Park TS, Huo JS, Peters A, Talbot CC Jr, Verma K, et al. (2012) Growth Factor-Activated Stem Cell Circuits and Stromal Signals Cooperatively Accelerate Non-Integrated iPSC Reprogramming of Human Myeloid Progenitors. PLoS ONE 7(8): e42838. doi:10.1371/journal.pone.0042838