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Middle East Fertility Society Journal
Middle East Fertility Society
ISSN: 1110-5690
Vol. 12, Num. 2, 2007, pp. 140-141
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Middle East Fertility Society Journal, Vol. 12, No. 2, 2007, pp .140-141
SHORT COMMUNICATION
A
Novel Method for Reprogramming Somatic Cells into Embryonic Stem Cells
Walid E Maalouf, MMedSc, PhD 1,2
INRA, UMR 1198; ENVA; CNRS, FRE 2857, Biologie du
Développement et Reproduction, Jouy en Josas, F-78350, France1, Department
Biologie II, LMU München, Grosshaderner Str. 2, 82152 Planegg-Martinsried,
Germany2.
Code Number: mf07024
Stem
cells are the bodys master cells, they are pluripotent cells, and in theory,
they can potentially be differentiated to any tissue-type in the body. Until
today, stem cells have been derived from the totipotent cells of the inner cell
mass (ICM) of mouse and human blastocysts. The ability of a differentiated
somatic cell to switch into a pluripotent cell has puzzled researchers for
several years. It was not until exactly ten years ago, when Dolly the sheep was
born (1) that scientists accepted the fact that somatic cells can be
reprogrammed into an embryonic totipotent state.
Dolly
was created after the transfer of a differentiated mammary gland cell nucleus
into a donor oocyte which reversed the somatic program into an embryonic one,
and developed to give rise to a live offspring.
Ten years after Dolly, an embryo-free
alternative method for the derivation of stem cells has now been proven
possible. In recent original research by Shinya Yamanaka of Kyoto University,
mouse skin cells were de-differentiated into an embryonic state by a simple
retroviral introduction of four genes that code for specific proteins known as
transcription factors, namely Oct3/4, Sox2, c-Myc and Klf4 (2). The resulting
cells were termed induced pluripotent cells or iPS cells. They carry analogous
expressed markers (Oct4, Nanog, Sox2 and Fbx15) and chromatin modifications
(DNA CpG dinucleotides, histone H3 lysine 4 and histone H3 lysine 27
methylation). In addition, iPS cells can multiply indefinitely in culture,
while maintaining their pluripotent state, similarly to existing stem cells
derived from embryos. In addition, iPS cells were selected according to their
Nanog expression, which is a target of Oct3/4 and Sox2.
The
selected cells were tested for their ability to produce adult chimaeric mice by
injecting them into blastocysts, which were then transplanted into the uteri of
pseudopregnant surrogates. Simple sequence length polymorphism (SSLP) was used
to demonstrate the contribution of these cells to various organs including the
testes. The germ line transmission was then tested by crossing the resulting
chimaeric mice for a second generation with limited success.
The
work by Yamanakas group could have come under severe scrutiny after the irreproducible
(later fraudulent) work by Woo Suk Hwang claiming to have innovatively derived
of embryonic stem cells from human cloned embryos. However, the replication of
Yamanakas results by Rudolf Jaenisch and his team (3) from the Whitehead
Institute of Biomedical Research in Cambridge, Massachusetts, as well as the
joint effort (4) between Konrad Hochedlinger of the Harvard Stem Cell Institute
in Boston, Massachusetts and Kathrin Path of the University of California, Los Angeles, corroborated the work of the Japanese team.
The
derivation of stem cells, without the need for eggs, sperm, or embryos, is the great
prize for stem cell research. In theory, one can speculate that individuals
iPS cells can be propagated in the laboratory and differentiated into any type
of cell in the body. But of course, the method is still far from perfect still,
and there is a high dose of scepticism surrounding it. The reprogramming of
cells is inefficient, with only less than 0.1% of skin cells that will be fully
reprogrammed. As in most gene knock-in experiments, antibiotic resistance genes
are inserted along the genes of interest. The cells are then supplemented with
antibiotics to destroy non-transfected cells.
The
major drawback of these experiments is the increased activation of tumour causing
genes such as the reactivation of c-Myc in the current studies. This
deregulation of certain factors can be the result of the utilization of
retroviruses as a method of transfecting cells, which introduce genes at random
locations in the genome. A thorough understanding about the molecular pathways
that dictate this reprogramming is needed. Alternative methods have are already
been suggested such as the replacement of the retrovirus by an adenovirus
system for transient expression, and as Alan Trounson of Monash University said
I can think of a dozen experiments right now and theyre all good ones.
These
findings have been particularly welcomed in the quarters where the use of embryos
for research is ethically opposed. Moreover, fellow researchers and the public
are already speculating about the application of these methods for human
celltherapy and treatment of diseases and disabilities like Parkinsons,
Alzheimer, Type 1 diabetes, strokes, and spinal cord injury. Therefore, whether
embryonic or somatic, the race is still on for the ultimate method and the
ultimate cells that will be employed in clinical medicine.
REFERENCES
- Wilmut I,
Schnieke AE, McWhir J, Kind AJ, Campbell KHS. Viable offspring derived from
fetal and adult mammalian cells. Nature 1997 February;385(6619):810-3.
- Okita K,
Ichisaka T, Yamanaka S. Generation of germline-competent induced pluripotent
stem cells. Nature 2007 June 6.
- Wernig M,
Meissner A, Foreman R, Brambrink T, Ku M, Hochedlinger K, Bernstein BE,
Jaenisch R. In vitro reprogramming of fibroblasts into a pluripotent
ES-cell-like state. Nature 2007 June 6.
- Maherali
N, Sridharan R, Xie W, Utikal J, Eminli S, Arnold K, Stadfeld M, Yachechko R,
Tchieu J, Jaenisch R, Plath K, Hochedlinger K. Directly reprogrammed
fibroblasts show global epigenetic remodeling and widespread tissue
contribution. Cell Stem Cell 2007;1:55-70.
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