Each individual develops from a single cell, which
is the fertilized egg. During the next
few days in the uterus, the egg multiplies into a number of similar cells. As time progresses, the cells get
differentiated into specialized tissues.
Similar tissues form organs, each of which performs definite functions.
John B. Gurdon and Shinya Yamanaka discovered that
the reverse is also possible. Their experiments, separated by a gap of
over 40 years, demonstrated that specialized cells can be converted into
immature cells, and these immature cells contain the information that can
enable them to again form specialized cells and tissues.
In his experiment conducted in 1962, John Gurdon
replaced the nucleus of the egg of a frog with a mature nucleus from an
intestinal cell of a tadpole. The
result - the modified egg cell developed into a tadpole.
Shinya Yamanaka conducted his experiments on mice in
2006 and took Gurdon's work a step further.
He introduced a few genes into mature cells and converted the same cells
into immature stem cells. These
immature cells, called induced pluripotent stem cells (iPS cells), could later
develop into mature cells.
These important findings have changed our outlook
regarding mature cells and have opened newer avenues for further studies in
understanding diseases and developing newer therapies.