| 1 | nature video | Method of the Year 2009: iPS cells | 76247 | 497 | 16 | 52.5 | negative | 5:26 | In 1996, the world's first cloned mammal, Dolly the sheep, was born. Her birth proved that the mammalian genome could travel back in time. Placed into an egg, the DNA of a specialised or differentiated cell gained the powers of an undifferentiated stem cell. Inactive parts of the genome were reawakened and directed the development of a whole new animal. Dolly's birth launched a race not to cloned people but to find a way to make human embryonic stem cells from a specific individual. Embryonic stem cells can make any sort of body tissue so this promised to provide tailor-made human cells for research and transplantation. But making cloned embryonic stem cells in the lab proved very difficult and on top of that, in 2005, the field was bruised by a high-profile fraud. Around this time, Shinha Yamannaka finished his own experiments. He'd found a way to make cells similar to cloned embryonic stem cells but without using eggs or embryos making the process much more straightforward. His technique was so revolutionary he worried other scientists wouldn't believe him. Using just four genes, Yamannaka had changed mature mouse cells into pluripotent stem cells, cells that could then be used to make almost any cell in the body. Yamannaka named his reprogrammed cells, induced pluripotent stem cells or IPS cells. At first, the scientific community was skeptical, but once Yamannaka revealed the identity of the four genes, other scientists quickly reproduced his work. One of these scientists was Conrad Hochheadlinger. He engineered his mouse cells to make green fluorescent protein whenever a crucial stem cell gene was active. Then he tried Yamannaka's reprogramming technique for himself. To his astonishment, his cells glowed green. They had indeed turned into stem cells. Hochheadlinger and other scientists showed that these stem cells were capable of turning into all kinds of tissue in mice, including heart tissue, skin and even sperm. Then came human cells. Just a few months later, more scientists showed that our own cells could also be rewound to a stem cell state. So much for cells in dishes, the ultimate test was to make healthy fertile mice entirely out of IPS cells. Recently, IPS cells rose to this challenge too. Nature methods has named IPS cells Method of the Year 2009 because of their promise as tools to study biology. Although IPS cells were first made some years ago, it's only now that they are beginning to be used in this way. Studying the cellular machinery that enables an IPS cell to turn into another cell type could help us understand what makes a nerve cell acquire the ability to transmit impulses or a heart cell to beat. Researchers are also excited about using IPS cells to study human diseases in human tissue, likely to be a more accurate way to model disease than using mouse models. One of the first studies to use IPS cells to study disease was by Clive Svensson. He made IPS cells from cells taken from a young boy with spinal muscular atrophy and then turned the IPS cells into neurons. This enabled him to study the differences between disease and healthy brain cells. There are still a few problems with this approach, not all cells that look like IPS cells have actually been thoroughly reprogrammed, so researchers are working on better ways to make an assess IPS cells on their offspring. And this work won't spell the end of embryonic stem cell research. Embryonic stem cells are still the best understood pluripotent cells, and it remains to be seen if IPS cells are entirely equivalent to them. But the IPS revolution has most definitely begun. In the last year, labs all over the world have published high profile papers, and many research groups are starting to make disease-specific IPS cell lines. In the next few years, these new additions to the biologists toolkit should start to show their full potential, increasing our understanding of human diseases and the basic workings of our cells. | ↗ |