Stem cells with the capacity to form any type of tissue can be created from adult cells without destroying embryos, according to a new research that suggests a way of sidestepping ethical controversy over the field.
Embryonic stem cells (ESCs) are found only in early embryos and are attractive to medical researchers as they are ‘pluripotent’ – they can give rise to all the 200 or so tissue types found in the human body. The goal is to find ways of directing their growth as they can be used to provide replacement tissue for treating conditions such as Parkinson’s, diabetes, and spinal paralysis. They are also the source of ethical controversy: the cells are derived from excess human embryos discarded after in vitro fertilization and obtaining them requires destruction of the embryos.
Two groups – one led by Shinya Yamanaka at Kyoto university in Japan and one led by Thompson and Junying Yu at the University of Wisconsin – separately engineered human skin cells to express 4 different genes. For reasons not yet clear, exposing cells to these genes appears to turn back the developmental clock. Both groups found that the resulting cells exhibit two major properties that define ESC’s – pluripotency divide indefinitely in their undifferentiated state. While the new cells look and act like ESCs, it is not yet clear just how similar they are. A screen of the expression of 30,000 genes showed that the pluripotent cells are similar but not identical to ESCs.
Both teams used viral DNA to introduce genes for 4 transcription factors – proteins that turn on other genes in the cell – into fibroblasts – a type of skin cell. Two of these transcription factors were the same in both groups; two were different. Scientists theorize that when expressed in adult cells. The transcription factors activate a genetic cascade that returns the cell and its DNA to an embryonic–like state. When implanted into mice, the cells generated a ball of tissue containing multiple differentiated cell types, a standard test for cell pluripotency. Yamanaka’s team also showed that the cells could differentiate into muscle and nerve cells, employing the same protocols used with ESCs.
Before these cells can be considered for human therapeutics, the researchers will need to develop an alternative way to express the transcription factors. The viruses currently used can integrate into genome and pose potential safety concerns. Germline transmission is the final and definitive proof that these cells can do anything a traditionally derived ESC can do.
There is still a long way to go, however!
Source:
http://www.technologyreview.com/biotech/19742
http://www.timesonline.co.uk/tol/news/uk/health/article1895546.ece
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