November 23, 2007

Stem Cells: In a Nutshell

Dolly, the cloned sheepStem cells are cells which have the ability to differentiate into any type of tissue. We can make any kind of tissue such as an eye or a piece of bone, using these pluripotential stem cells. Thus if you have a damaged liver, just culture some stem cells and program them to grow into hepatic tissues. Replace your damaged liver with these cultured liver cells, you've got a fresh lease of life!

Ian Wilmut, professor and Head of the Department of Gene Expression and Development at the Roslin Institute near Edinburgh, Scotland, created the first clone derived from adult cells. He named it Dolly, after the celebrated singer Dolly Parton. The mechanism of its creation involved taking of cells from a sheep's udder and let it undergo some processes that involved specific nutritional starvation so that the skin cell forgot what it was and went back to its primitive undifferentiated stage. Normally, in a cell all the genetic components are there but the expression of them varies depending on the tissues involved. The genome of our eye (ophthalmic) cells are exactly the same as that of the liver cells: only difference is that some genes are silenced or switched off while some are on.

But the process involved is a tedious one. Now,
Shinya Yamanaka of Kyoto University in Japan, have transformed mouse tail cells into embryonic stem cells using a much simpler technique. He used a retrovirus (which cause a type of leukemia and the dreaded disease AIDS and many others), and modified it so that its virulence was lost. He then introduced 4 regulator genes (OCT3/4, SOX2, KLF4, and c-MYC) in it, and let it mix with the skin cells taken from the facial skin of a 36-year-old woman in a petridish. Retroviruses, having the enzyme reverse transcriptase or RNA dependent DNA polymerase, has the ability to integrate the DNA into the dermal genome. There's a change of guard now. The dermal genome goes back in time as it becomes a stem cell as dictated by the 4 genes.

The advantage of this technique, apart from ease of manipulation, is the bypassing of moral and ethical dilemmas, that cropped up in the course of time. You no longer have to tinker with live embryos (as the US senate or the Papal office might have objections). One could grow organs for transplantation, perform clinical trials of drugs and even study cellular and molecular biological processes. Disease processes like Alzheimer's Dementia, Parkinson's Disease, other neurological diseases and cancer are some examples where cloning might throw some light upon. Attendant risks include formation of tumors due to the retroviral vector. In any case cloning is set to become commonplace anytime soon.

So, time to get ready for a doppleganger?

Last modified: 18 Oct 2009
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