Histones may hold the key to the generation of totipotent stem cells

Feb 06, 2014
Histones may hold the key to the generation of totipotent stem cells
This image shows iPS cells (green) generated using histone variants TH2A and TH2B and two Yamanaka factors (Oct3/4 and Klf4). Credit: RIKEN

One major challenge in stem cell research has been to reprogram differentiated cells to a totipotent state. Researchers from RIKEN in Japan have identified a duo of histone proteins that dramatically enhance the generation of induced pluripotent stem cells (iPS cells) and may be the key to generating induced totipotent stem cells.

Differentiated cells can be coaxed into returning to a stem-like pluripotent state either by artificially inducing the expression of four factors called the Yamanaka factors, or as recently shown by shocking them with sublethal stress, such as low pH or pressure. However, attempts to create totipotent capable of giving rise to a fully formed organism, from , have failed.

The study, published today in the journal Cell Stem Cell and led by Dr. Shunsuke Ishii from RIKEN, sought to identify the molecule in the mammalian oocyte that induces the complete reprograming of the genome leading to the generation of totipotent . This is the mechanism underlying normal fertilization, as well as the cloning technique called Somatic-Cell Nuclear Transfer (SCNT).

SCNT has been used successfully to clone various species of mammals, but the technique has serious limitations and its use on human cells has been controversial for ethical reasons.

Ishii and his team chose to focus on two histone variants named TH2A and TH2B, known to be specific to the testes where they bind tightly to DNA and affect gene expression.

Histones may hold the key to the generation of totipotent stem cells
This is a Chimera mouse (grey) generated with iPS cells induced using the histone variants TH2A and TH2B and 2 Yamanaka factors. Its offspring show the agouti coat color, indicating that all tissues are derived from the iPS cells described above. Credit: RIKEN

The study demonstrates that, when added to the Yamanaka cocktail to reprogram mouse fibroblasts, the duo TH2A/TH2B increases the efficiency of iPSC cell generation about twentyfold and the speed of the process two- to threefold. And TH2A and TH2B function as substitutes for two of the Yamanaka factors (Sox2 and c-Myc).

By creating knockout mice lacking both proteins, the researchers show that TH2A and TH2B function as a pair, are highly expressed in oocytes and fertilized eggs and are needed for the development of the embryo after fertilization, although their levels decrease as the embryo grows.

In the early embryo, TH2A and TH2B bind to DNA and induce an open chromatin structure in the paternal genome, thereby contributing to its activation after fertilization.

These results indicate that TH2A/TH2B might induce reprogramming by regulating a different set of genes than the Yamanaka factors, and that these genes are involved in the generation of totipotent cells in oocyte-based reprogramming as seen in SCNT.

"We believe that TH2A and TH2B in combination enhance reprogramming because they introduce a process that normally operates in the zygote during fertilization and SCNT, and lead to a form of reprogramming that bears more similarity to oocyte-based reprogramming and SCNT" explains Dr. Ishii.

Explore further: New hope for stem cells, regenerative medicine emerges from the lab

More information: Shinagawa T, Takagi T, Tsukamoto D, Tomaru C, Huynh LM, Sivaraman P, Kumarevel T, Inoue K, Nakato R, Katou Y, Sado T, Takahashi S, Ogura A, Shirahige K, Ishii S. "Histone Variants Enriched in Oocytes Enhance Reprogramming to Induced Pluripotent Stem Cells", Cell Stem Cell 14, 2014

add to favorites email to friend print save as pdf

Related Stories

Rethinking reprogramming: A new way to make stem cells

Apr 07, 2011

A paper published by Cell Press in the April 8th issue of the journal Cell Stem Cell reveals a new and more efficient method for reprogramming adult mouse and human cells into an embryonic stem cell-like state and could ...

Researchers create embryonic stem cells without embryo

Jan 29, 2014

(Phys.org) —Since the discovery of human embryonic stem cells, scientists have had high hopes for their use in treating a wider variety of diseases because they are pluripotent, which means they are capable ...

The developmental on-switch

Aug 19, 2013

German researchers have demonstrated for the first time why the molecular cocktail responsible for generating stem cells works. Sox2 and Oct4 are proteins whose effect on cells resembles that of an eraser: ...

Recommended for you

Cohesin molecule safeguards cell division

Nov 21, 2014

The cohesin molecule ensures the proper distribution of DNA during cell division. Scientists at the Research Institute of Molecular Pathology (IMP) in Vienna can now prove the concept of its carabiner-like ...

Nail stem cells prove more versatile than press ons

Nov 21, 2014

There are plenty of body parts that don't grow back when you lose them. Nails are an exception, and a new study published in the Proceedings of the National Academy of Sciences (PNAS) reveals some of the r ...

Scientists develop 3-D model of regulator protein bax

Nov 21, 2014

Scientists at Freie Universität Berlin, the University of Tubingen, and the Swiss Federal Institute of Technology in Zurich (ETH) provide a new 3D model of the protein Bax, a key regulator of cell death. When active, Bax ...

Researchers unwind the mysteries of the cellular clock

Nov 20, 2014

Human existence is basically circadian. Most of us wake in the morning, sleep in the evening, and eat in between. Body temperature, metabolism, and hormone levels all fluctuate throughout the day, and it ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.