The new study, which will be published online Nov. 18 in Nature, showed that what seemed to be changes in iPS cells' genetic makeup — presumed to be inflicted either in the course of their generation from adult cells or during their propagation and maintenance in laboratory culture dishes — instead are often accurate reflections of existing but previously undetected genetic variations among the cells comprising our bodies.
That's good news for researchers hoping to use the cells to study disease or, someday, for regenerative medicine. But it raises the question of whether and to what extent we humans are really walking mosaics whose constituent cells differ genetically from one to the next in possibly significant respects, said Alexander Urban, PhD, assistant professor of psychiatry and behavioral sciences. Urban shared senior authorship of the study with bioinformatics professor Mark Gerstein, PhD, and neurobiology professor Flora Vaccarino, MD, both of Yale.
It's only a few years ago that human iPS cells started becoming available to researchers. These cells hold great promise because they act almost exactly like embryonic stem cells, which can be nudged to differentiate into virtually any of the body's roughly 200 different cell types. But iPS cells can be derived easily from a person's skin, alleviating numerous ethical concerns arising from the necessity of obtaining embryonic stem cells from fertilized eggs.
At least in principle, iPS cells' genetic makeup closely reflects that of the individual from whom they were derived. Today, "heart cells" derived from a heart patient's skin can be produced in a laboratory dish so scientists can learn more about that particular patient's condition and to screen drugs that might treat it. Tomorrow, perhaps, such cells could be administered to that patient to restore heart health without being perceived as foreign tissue by the patient's immune system, which would otherwise reject the implanted cells.
However, Urban said, several previous studies have raised worries regarding iPS cells' genomic stability. Whether it was the reprogramming procedure researchers use to convert ordinary adult cells into iPS cells or the culturing techniques employed to keep them alive and thriving afterward, something appeared to be inducing an upswing in these cells' manifestation of copy number variations, or CNVs — the disappearance or duplication of chunks of genetic material at specific locations along the vast stretches of DNA that coil to form the chromosomes residing in all human cells.
CNVs dot everybody's genomes. They occur naturally because of DNA-copying errors made during cell replication, and accumulate in our genomes over evolutionary time. The human genome, taken as a whole, is a DNA sequence consisting of four varieties of chemical units, strung together like beads on a roughly 3-billion-bead-long necklace. CNVs range in length from under 1,000 DNA units to several million. They account for up to several percent of the entire human genome, making them a major source of genetic differences between people.
But if either iPS cells' mode of generation or their subsequent maintenance in culture were promoting an increase in CNVs, it would seriously compromise these cells' utility in research and pose a fatal flaw to their use in regenerative medicine, said Urban. "You would never want to introduce iPS cells into a patient thinking that these cells had the same genome as the rest of the patient's cells, when in fact they had undergone substantial genetic modifications you knew nothing about, much less their effects," said Urban. (Similar concerns apply to embryonic stem cells.)
To see how serious a problem CNVs might pose for iPS cells' use, the collaborators performed tiny skin biopsies on seven volunteers and extracted cells called fibroblasts, which abound in skin and are amenable to cell culture in general and iPS cell generation in particular. From these, the team produced 20 separate iPS cell lines in culture. Using now-standard lab methods, the investigators determined, chemical unit by chemical unit, the full genomic sequence of the cells composing each new iPS cell line.
Urban and his colleagues, who had likewise assessed the fibroblasts from which the lines were derived, compared their genomic sequences with those of the newly generated iPS cells. The scientists were able to pinpoint numerous CNVs in the new cells that hadn't shown up in the fibroblasts. This raised the possibility that the rigors of reprogramming or life in a dish, or both, had led to new CNVs in the cells.
But the technique used to determine the full-length genome sequences of iPS cells and the "parental" fibroblasts from which they'd been spawned analyzes not single cells but millions at a time. So a CNV residing in only a minority of cells within this mix could easily be missed, its signal swamped by the noise of the majority report.
Armed with knowledge of the precise locations along the genome where each of the "new" CNVs had popped up in their iPS cell lines, the scientists went back to the fibroblasts. This time, they used an analytical tool that, like a photocopying machine, can generate millions or billions of copies of a single section of DNA — provided that the specific DNA section is present to begin with. For each "new" CNV that had been unearthed in the iPS cells, a different version of this molecular copying machine was employed.
"Lo and behold, in many cases, this technique unearthed CNVs in the fibroblasts that were there all along but had been missed in the earlier, mass analysis," Urban said. These CNVs had gone undetected because the fibroblasts in which they resided represented as little as a fraction of a percent of the fibroblasts in a biopsy sample. But any CNV in a fibroblast lucky enough to become the "parent" of the billions of iPS cells bearing its identical genomic "face" would now stick out like the proverbial sore thumb. Six out of the 20 different iPS cell lines sported at least one CNV unshared with the other lines, the investigators found. To the extent this reflects differences in parental fibroblasts, it means about 30 percent of the cells in human skin may harbor unique CNVs.
"This is a huge amount of cell-to-cell genetic variation," said Urban, who also participated in a recent study of human tissues conducted by the laboratory of Michael Snyder, PhD, professor and chair of genetics at Stanford. That study showed there can be distinct CNV patterns in kidney, pancreas and liver. "Rather than monoliths, our bodies may be mosaics composed of cells whose genomes differ. What we do not know is whether or when these differences are dangerous, irrelevant or beneficial."
That may depend on the organ, said Urban. "The more complicated something is, the more ways there are that something could go wrong with it. The brain is a particularly complicated organ. CNVs affecting cells in particular brain structures or areas could be playing a role in complex neurodevelopmental disorders such as schizophrenia and autism." Urban intends to find out, he said.
Michael Haney, a research technician in the Urban lab, and several Yale investigators co-authored the study, which was funded by the National Institute of Mental Health, the Simons Foundation and the Stanford University School of Medicine.
Information about the school's Department of Psychiatry and Behavioral Sciences, which also supported this work, is available at http://psychiatry.stanford.edu/.
The Stanford University School of Medicine consistently ranks among the nation's top medical schools, integrating research, medical education, patient care and community service. For more news about the school, please visit http://mednews.stanford.edu. The medical school is part of Stanford Medicine, which includes Stanford Hospital & Clinics and Lucile Packard Children's Hospital. For information about all three, please visit http://stanfordmedicine.org/about/news.html.PRINT MEDIA CONTACT: Bruce Goldman at (650) 725-2106 (firstname.lastname@example.org)
Bruce Goldman | EurekAlert!
Further reports about: > CNV > DNA > Medicine > adult cells > brain structure > cell type > developmental disorder > embryonic stem > embryonic stem cell > genetic makeup > genetic variation > genome sequence > human cell > human genome > human tissue > iPS cells > mental disorder > regenerative medicine > single cell > stem cells
New mechanisms uncovered explaining frost tolerance in plants
26.09.2016 | Technische Universität München
Chains of nanogold – forged with atomic precision
23.09.2016 | Suomen Akatemia (Academy of Finland)
The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP has been developing various applications for OLED microdisplays based on organic semiconductors. By integrating the capabilities of an image sensor directly into the microdisplay, eye movements can be recorded by the smart glasses and utilized for guidance and control functions, as one example. The new design will be debuted at Augmented World Expo Europe (AWE) in Berlin at Booth B25, October 18th – 19th.
“Augmented-reality” and “wearables” have become terms we encounter almost daily. Both can make daily life a little simpler and provide valuable assistance for...
With the help of artificial intelligence, chemists from the University of Basel in Switzerland have computed the characteristics of about two million crystals made up of four chemical elements. The researchers were able to identify 90 previously unknown thermodynamically stable crystals that can be regarded as new materials. They report on their findings in the scientific journal Physical Review Letters.
Elpasolite is a glassy, transparent, shiny and soft mineral with a cubic crystal structure. First discovered in El Paso County (Colorado, USA), it can also be...
For the first time, Fraunhofer IKTS shows additively manufactured hardmetal tools at WorldPM 2016 in Hamburg. Mechanical, chemical as well as a high heat resistance and extreme hardness are required from tools that are used in mechanical and automotive engineering or in plastics and building materials industry. Researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden managed the production of complex hardmetal tools via 3D printing in a quality that are in no way inferior to conventionally produced high-performance tools.
Fraunhofer IKTS counts decades of proven expertise in the development of hardmetals. To date, reliable cutting, drilling, pressing and stamping tools made of...
At AKL’16, the International Laser Technology Congress held in May this year, interest in the topic of process control was greater than expected. Appropriately, the event was also used to launch the Industry Working Group for Process Control in Laser Material Processing. The group provides a forum for representatives from industry and research to initiate pre-competitive projects and discuss issues such as standards, potential cost savings and feasibility.
In the age of industry 4.0, laser technology is firmly established within manufacturing. A wide variety of laser techniques – from USP ablation and additive...
Every three years, the plastics industry gathers at K, the international trade fair for plastics and rubber in Düsseldorf. The Fraunhofer Institute for Laser Technology ILT will also be attending again and presenting many innovative technologies, such as for joining plastics and metals using ultrashort pulse lasers. From October 19 to 26, you can find the Fraunhofer ILT at the joint Fraunhofer booth SC01 in Hall 7.
K is the world’s largest trade fair for the plastics and rubber industry. As in previous years, the organizers are expecting 3,000 exhibitors and more than...
23.09.2016 | Event News
20.09.2016 | Event News
16.09.2016 | Event News
26.09.2016 | Physics and Astronomy
26.09.2016 | Physics and Astronomy
26.09.2016 | Life Sciences