Gene knockout Mice Technology- The Nobel for Physiology or Medicine, 2007

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Photo Description - Noble Laureates from Left: 

1. Prof. Mario R. Capecchi  (6 October 1937 -)                                                

2. Sir Martin J. Evans (1 January 1941  -)                               

3. Prof Oliver Smithies (23 Jun1925- 10 Jan 2017)         

Genetic diseases are caused by mutations in our DNA. Experiments cannot be carried out on humans to study how mutations in gene cause diseases. Experimental model organisms are used to create such mutations and study their effect on physiology and health.  Mice are mammals and genetically very close to humans and many mutations that cause disease in humans also cause same disease in mice. Gene function can be deleted in mice by gene knock out technology.  Thousands of the genes in mice have been knocked out and studied. This has led to understanding of many human diseases and discovery of drugs for many diseases. The 2007 Nobel Prize for physiology or medicine was awarded to two US scientists Mario Capecchi, Oliver Smithies and a British scientist Sir Martin Evans for their pioneering work in developing this technology.  The technology involves two major steps

1. Creating a deletion in the specific gene of interest

2. To have cells that can carry and transfer this mutation to the progeny.

Capecchi and Smithies used a method called homologous recombination, which is very prevalent in bacteria to show that genes can be deleted in mammalian cells using a modified homologous recombination method. The method involved making DNA molecules having similarity with the gene to be knocked out.  The DNA molecule would carry the required deletion. When introduced into the mammalian cell the DNA molecules recognize the target gene by similar DNA sequence and replace the original gene with the provided deletion DNA. They also developed a positive and negative selection method using antibiotic selection genes to increase the efficiency of generating gene knock out cells. However the mammalian cells they were using could not be incorporated into the animals or the deletion could be transferred to the next generation or progeny to create a gene knock out animal. Meanwhile in Britain, Martin Evans was working on embryonal carcinoma cells, which had the ability to differentiate to all types of cells in the body.

These cells could not differentiate to germ cells which give rise to the gametes to form the next generation of animals. In the early 80’s Martin Evans isolated cells from the early mouse embryo, which were capable of differentiating into germ cells, these are popularly known today as embryonic stem cells. Martin Evans introduced viral DNA into the embryonic stem cells. He transferred these cells into early mouse embryo and derived mice having cells from the embryo and the embryonic stem cells called as chimeric mice. The viral DNA in the embryonic stem cells was now present in some of the cells of the chimeric mice. Some of these cells made the gametes, which carried the viral DNA to the next generation confirming that any changes made to the DNA of embryonic stem cells can be passed onto the next generation of mice.

The gene knock out mice technology was born by synthesizing together homologous recombination and the embryonic stem cell technologies. Using homologous recombination method, a gene knock out embryonic stem cell was created. The gene knockout embryonic stem cells were transferred into a mouse embryo to derive chimeric mice. The chimeric mice passed on the genetic deletion to the next generation of mice giving rise to the first gene knock out mice. Today many variants and advanced methods of technologies are available for generating the gene knock out mice. The gene knock out mice technology has contributed immensely in understanding of human disease like cancer, heart disease, genetic disease, neurological disorders, diabetes etc. this has eventually led to discovery of new drugs to many human diseases. In the recent times, the gene knock out technology has also been adopted in other laboratory animals like rats.

 

Article By:

Dr. P Chandra Shekar

Senior scientist

CSIR-Centre for Cellular and Molecular Biology

Hyderabad – 500007

Email: csp@ccmb.res.in

Posted By : ScienceIndia Administrator
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