Stem cells are key to the promise of regenerative medicine: the repair or replacement of injured tissues with custom grown substitutes. Essential to this process are induced pluripotent stem cells (iPSCs), which can be created from a patient's own tissues, thus eliminating the risk of immune rejection.
For the first time, the Belmonte laboratory has replaced OCT4, one gene previously thought indispensable for the reprogramming of human cells into embryonic-like cells. The picture shows newly reprogrammed cells expressing marks of pluripotency as identified by fluorescence (NANOG in green, TRA-1-81 in red).
Credit: Courtesy of the Salk Institute for Biological Studies
However, Shinya Yamanaka's formula for iPSCs, for which he was awarded last year's Nobel Prize, uses a strict recipe that allows for limited variations in human cells, restricting their full potential for clinical application.
Now, in this week's issue of Cell Stem Cell, the Salk Institute's Juan Carlos Izpisua Belmonte and his colleagues show that the recipe for iPSCs is far more versatile than originally thought. For the first time, they have replaced a gene once thought impossible to substitute, creating the potential for more flexible recipes that should speed the adoption of stem cells therapies.
Stem cells come in two types: embryonic stem cells (ESCs), which are immature cells that have never differentiated into specific cell types, and induced pluripotent stem cells, which are mature cells that have been reprogrammed back into an undifferentiated state. After the initial discovery in 2006 by Yamanaka that introducing four different genes into a mature cell could suffice for reprogramming the cell to pluripotency, most researchers adopted his recipe.
Izpisua Belmonte and his colleagues took a fresh approach and discovered that pluripotency (the stem cell's ability to differentiate into nearly any kind of adult cell) can also be accomplished by balancing the genes required for differentiation. These genes code for "lineage transcription factors," proteins that start a stem cell down the path to differentiate first into a particular cell lineage, or type, such as a blood cell versus a skin cell, and then finally into a specific cell, such as a white blood cell.
"Prior to this series of experiments, most researchers in the field started from the premise that they were trying to impose an 'embryonic-like' state on mature cells," says Izpisua Belmonte, who holds the Institute's Roger Guillemin Chair. "Accordingly, major efforts had focused on the identification of factors that are typical of naturally occurring embryonic stem cells, which would allow or further enhance reprogramming."
Despite these efforts, there seemed to be no way to determine through genetic identity alone that cells were pluripotent. Instead, pluripotency was routinely evaluated by functional assays. In other words, if it acts like a stem cell, it must be a stem cell.
That condition led the team to their key insight. "Pluripotency does not seem to represent a discrete cellular entity but rather a functional state elicited by a balance between opposite differentiation forces," says Izpisua Belmonte.
Once they understood this, they realized the four extra genes weren't necessary for pluripotency. Instead, it could be achieved by altering the balance of "lineage specifiers," genes that were already in the cell that specified what type of adult tissue a cell might become.
"One of the implications of our findings is that stem cell identity is actually not fixed but rather an equilibrium that can be achieved by multiple different combinations of factors that are not necessarily typical of ESCs," says Ignacio Sancho-Martinez, one of the first authors of the paper and a postdoctoral researcher in Izpisua Belmonte's laboratory.
The group was able to show that more than seven additional genes can facilitate reprogramming to iPSCs. Most importantly, for the first time in human cells, they were able to replace a gene from the original recipe called Oct4, which had been replaced in mouse cells, but was still thought indispensable for the reprogramming of human cells. Their ability to replace it, as well as SOX2, another gene once thought essential that had never been replaced in combination with Oct4, demonstrated that stem cell development must be viewed in an entirely new way.
"It was generally assumed that development led to cell/tissue specification by 'opening' certain differentiation doors," says Emmanuel Nivet, a post-doctoral researcher in Izpisua Belmonte's laboratory and co-first author of the paper, along with Sancho-Martinez and Nuria Montserrat of the Center for Regenerative Medicine in Barcelona, Spain.
Instead, the successful substitution of both Oct4 and SOX2 shows the opposite. "Pluripotency is like a room with all doors open, in which differentiation is accomplished by 'closing' doors," Nivet says. "Inversely, reprogramming to pluripotency is accomplished by opening doors."
The team believes their work should help to overcome one of the major hurdles to the widespread adoption of stem cell therapies: the original four genes used to reprogram stem cells had been implicated in cancer. "Recent studies in cancer, many of them done by my Salk colleagues, have shown molecular similarities between the proliferation of stem cells and cancer cells, so it is not surprising that oncogenes [genes linked to cancer] would be part of the iPSC recipe," says Izpisua Belmonte.
With this new method, which allows for a customized recipe, the team hopes to push therapeutic research forward. "Since we have shown that it is possible to replace genes thought essential for reprogramming with several different genes that have not been previously involved in tumorigenesis, it is our hope that this study will enable iPSC research to more quickly translate into the clinic," says Izpisua Belmonte.
Other researchers on the study were Tomoaki Hishida, Sachin Kumar, Yuriko Hishida, Yun Xia and Concepcion Rodriguez Esteban of the Salk Institute; Laia Miquel and Carme Cortina of the Center of Regenerative Medicine in Barcelona, Spain.
The work was supported by the Leona M. and Harry B. Helmsley Charitable Trust, F.M. Kirby Foundation, the G. Harold and Leila Y. Mathers Charitable Foundation, Nomis Foundation, Fundacion Cellex, the Ministerio de Economia y Competitividad (MINECO), TERCEL-ISCIII- MINECO and Cardiocel.
Kat Kearney | EurekAlert!
Further reports about: > Gates Foundation > Regenerative Therapien > Sox2 > Stem cell > Stem cell innovation > blood cell > cell death > cell type > different genes > doctoral research > embryonic stem > embryonic stem cell > human cell > induced pluripotent stem > induced pluripotent stem cell > pluripotency > pluripotent stem > pluripotent stem cells > stem cells > transcription factor
Bacteria as pacemaker for the intestine
22.11.2017 | Christian-Albrechts-Universität zu Kiel
Researchers identify how bacterium survives in oxygen-poor environments
22.11.2017 | Columbia University
The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.
Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
22.11.2017 | Business and Finance
22.11.2017 | Physics and Astronomy
22.11.2017 | Physics and Astronomy