As kids, we study a wide range of subjects in school, from
English to Social Studies and Science and even Music and Dance. But as we
progress to Senior School, we choose a specific “Group”, be it Biology, Commerce
or Computer Science. When we move into college for graduate and post graduate
degrees, our education becomes still more specialized. We dig deeper into a
specific subject and soon reach a state where we forget the basics of the other
subjects we learnt as kids. For most of us, this signifies a point of no
return, a stage when we are already lawyers, engineers or doctors and there is no way to go
back in time to make a drastic career change.
This social experience mirrors what was always believed to happen
in nature. We start our life as a single cell embryo which divides to give rise
to cells that are capable of forming the entire organism. These multi-potential
cells are called stem cells (specifically embryonic stem cells as they are
found in the embryo). But with each subsequent division, the new cells become
highly specialized, committed to performing unique functions. Some of the cells
mature into muscle cells, some become fat cells, and some turn into nerve cells
and together make a functional organism, whether it is a mouse or a human
being.
One of the most interesting questions in Biology was, like many
individuals in their career path, have these cells too reached a point of no
return? Can they no longer give rise to
any other cell type except the kind they are committed to form? Or can the
mature adult cells be reprogrammed to revert to their earlier uncommitted
state?
This year’s Nobel Prize for Physiology or Medicine, honors
two scientists who answered the latter question with a resounding “Yes, the
adult human cells are indeed reprogrammable! “ Sir John B. Gurdon of U.K and
Shinya Yamanaka of Japan have been awarded the 2012 prize for the discovery
that mature cells can be reprogrammed to become pluripotent (cells capable of
giving rise to many different kinds of cells).
Remember Dolly, the sheep, which made “cloning” a household
word in the early 90’s? She was created
by a process of nuclear transfer where the nucleus of the cell, which contains
the entire genetic information of the organism, was taken out of an adult sheep
cell and placed inside an enucleated egg cell, to form an embryo.
John Gurdon performed such a nuclear transfer in 1962. For
the first time he showed that the nucleus of a mature frog intestinal cell,
when placed inside an egg cell which had its nucleus removed, could reprogram
itself and regain its non- specialized nature. The reprogrammed cell divided like
a regular embryo and successfully produced live tadpoles, paving the way for research
that led to the creation of Dolly. This revolutionary experiment disproved the
dogma that adult cells are irreversibly committed into specialized cell
types.
But nuclear transfer into enucleated egg cells is a
difficult process. It also raises
ethical questions about using human egg cells and playing God by creating human
embryos that have to be destroyed to obtain the stem cells from them. In a
quest to find an alternate route to reprogram mature adult cells into
pluripotent stem cells, Shinya Yamanaka resorted to a totally different
approach. He identified genes that are responsible for the non- specialized nature
of embryonic stem cells. He then expressed these genes in the mature adult cells.
And viola! He could convert the mature committed cells into immature stem cells
that had the potential to give rise to many different cell types. The creation
of these cells, termed induced pluripotent stem cells (iPSCs), first published
in 2006, marked a significant development in cellular biology.
Together, these two discoveries changed our understanding
about development of cells and by extension, the whole organism. They opened up
the tantalizing prospect of creating different cell types including skin and
liver from adult cells. Imagine the possibility of regenerating any tissue that
has been lost by accident or disease! The iPSCs created from diseased
individuals would also be of great value in screening drugs for treatment.
Of course, more research has to be carried out into the
safety and practicality of using these cells in humans for therapy and improved
methods have to be devised for creating these cells. But today, let us
celebrate two individuals who have been bestowed with one of the highest honors
for their contributions to the advancement of science.
