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of the cell. Simply speaking, a differentiation process refers to how a cell is divided
into new cells. Cells in the next generation, in general, become more specialized
than their parent generation. Cells with the broadest range of potential can produce
all kinds of cells in an organism. This potential is called totipotency. The next
level of potency is called pluripotency, which means very many in its Latin origin
plurimus. A pluripotent cell can differentiate into more specialized cells. In contrast,
a unipotent cell can differentiate into only one cell type.
Prior to the work of Gurdon and Yamanaka, it was generally believed that the
path of cell differentiation is irreversible in that the potency of a cell becomes more
and more limited in generations of differentiated cells. Induced pluripotent stem
cells (iPS cells) result from a reprogramming of the natural differentiation. Starting
with a non-pluripotent cell, human intervention can reverse the process so that the
non-pluripotent cell could regain a more generic potency.
John B. Gurdon discovered in 1962 that the DNA of a mature cell may still have
all the information needed to develop all cells in a frog. He modified an egg cell of
a frog by replacing its immature nucleus with the nucleus from a mature intestinal
cell. The modified egg cell developed into a normal tadpole. His work demonstrated
that the specialization of cells is reversible. Shinya Yamanaka's discovery was made
more than 40 years later. He found out how mature cells in mice could be artificially
reprogrammed to become induced pluripotent stem cells.
8.2.1
A Scientometric Review
On August 25, 2011, more than a year ago before the 2012 Nobel Prize was
announced, I received an email from Emma Pettengale. She is the Editor of a
peer-reviewed journal Expert Opinion on Biological Therapy (EOBT). The journal
provides expert reviews of recent research on emerging biotherapeutic drugs and
technologies. She asked if I would be interested in preparing a review of emerging
trends in regenerative medicine using CiteSpace and she would give me 3 months
to complete the review.
EOBT is a reputable journal with an impact factor of 3.505 according to the
Journal Citation Report (JCR) compiled by Thomson Reuters in 2011. Emma's
invitation was an unusual one. The journal is a forum for experts to express their
opinions on emerging trends but I am not a specialist in regenerative medicine at
all. Although CiteSpace has been used in a variety of retrospective case studies,
including terrorism, mass extinctions, string theory, and complex network analysis,
we were able to find independent reviews of most of the case studies to cross validate
our results or contact domain experts to verify specific patterns. The invitation was
both challenging and stimulating. We would be able to analyze emerging trends in
a rapidly advancing field with CiteSpace. Most importantly, we wanted to find out
if we can limit our source of information exclusively to patterns that are obviously
identified by CiteSpace.
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