Key Protein Reveals Secret of Stem Cell Pluripotency

Key Protein Reveals Secret of Stem Cell Pluripotency
Monday, 05 September 2011

A protein that helps maintain mouse stem cell pluripotency has been identified by researchers at the RIKEN Omics Science Center. The finding, published in the August issue of Stem Cells (first published online July 26, 2011), points the way to advances in regenerative medicine and more effective culturing techniques for human pluripotent stem cells.

Diagram of the Ccl2 and leukemia inhibitory
factor (LIF) signal pathways integrating into
the transcription network. Known LIF signal
pathway is shown with black arrow. Our finding
of Ccl2 signal pathway for promoting
pluripotency is shown as dot black arrow.
Abbreviations: IL-6R, interleukin-6 receptor;
LIF, leukemia inhibitory factor; LIFR,
leukemia inhibitory factor receptor; NC,
negative control; PI(3)K, phosphoinositide
3-kinase.

Through their capacity to differentiate into any other type of cell, embryonic stem cells (ES cells) and induced-pluripotent stem cells (iPS cells) promise a new era of cell-based treatments for a wide range of conditions and diseases. Cultivating such cells, however, commonly relies on the use of so-called "feeder" cells to maintain pluripotency in cell culture conditions. Feeder cells keep stem cells in their undifferentiated state by releasing nutrients into the culture medium, but they have the potential to introduce contamination which, in humans, can lead to serious health risks.

Previous research has shown that mouse pluripotent stem cells can be cultured without feeder cells through the addition of a cytokine called Leukemia Inhibitory Factor (LIF) to the culture media ("feeder-free" culture). LIF is secreted by mouse feeder cells and activates signal pathways reinforcing a stem cell regulatory network. The researchers discovered early in their investigation, however, that the amount of LIF secreted from feeder cells is much less than the amount needed to maintain pluripotency in feeder-free conditions. This points to other, as-of-yet unknown contributing factors.

To clarify these factors, the research group analyzed differences in gene expression between mouse iPS cells cultured on feeder cells and those cultured in feeder-free (LIF treated) conditions. Their results revealed 17 genes whose expression level is higher in feeder conditions. To test for possible effects on pluripotency, they then selected 7 chemokines (small proteins secreted by cells) from among these candidates and overexpressed them in iPS cells grown in feeder-free conditions. They found that one chemokine in particular, CC chemokine ligand 2 (CCL2), enhances the expression of key pluripotent genes via activation of a well-known signal pathway known as Jak/Stat3.

While CCL2 is known for its role in recruiting certain cells to sites of infection or inflammation, the current research is the first to demonstrate that it also helps maintain iPS cell pluripotency. The findings also offer broader insights applicable to the cultivation of human iPS/ES cells, setting the groundwork for advances in regenerative medicine.

Source: RIKEN
Contact: Harukazu Suzuki

Reference:
CC Chemokine Ligand 2 and Leukemia Inhibitory Factor Cooperatively Promote Pluripotency in Mouse Induced Pluripotent Cells
Yuki Hasegawa, Naoko Takahashi, Alistair R. R. Forrest, Jay W. Shin, Yohei Kinoshita, Harukazu Suzuki and Yoshihide Hayashizaki.
Stem Cells, 2011, DOI: 10.1002/stem.673
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lincRNAs are Directing Embryonic Stem Cells Differentiation

New roles emerge for non-coding RNAs in directing embryonic development
Monday, 29 August 2011

Scientists at the Broad Institute of MIT and Harvard have discovered that a mysterious class of large RNAs plays a central role in embryonic development, contrary to the dogma that proteins alone are the master regulators of this process. The research, published online August 28 in the journal Nature, reveals that these RNAs orchestrate the fate of embryonic stem (ES) cells by keeping them in their fledgling state or directing them along the path to cell specialization.

lincRNAs orchestrate the fate of embryonic

stem cells (shown here) by keeping them in

their fledgling state or directing them along

the path to cell specialization.
Image courtesy of Alex Meissner.

Broad scientists discovered several years ago that the human and mouse genomes encode thousands of unusual RNAs — termed large, intergenic non-coding RNAs (lincRNAs) — but their role was almost entirely unknown. By studying more than 100 lincRNAs in ES cells, the researchers now show that these RNAs help regulate development by physically interacting with proteins to coordinate gene expression and suggest that lincRNAs may play similar roles in most cells.

“There’s been a lot of debate about what lincRNAs are doing,” said Eric Lander, director of the Broad Institute and the senior author of the paper.

“It’s now clear that they play critical roles in regulating developmental decisions — that is, cell fate. This was a big surprise, because specific types of proteins have been thought to be the master controls of development.”

“This is the first global study of lincRNAs,” said Mitchell Guttman, first author of the paper and a graduate student at MIT and the Broad Institute.

“We picked embryonic stem cells in particular because they are so important to development and so well understood. This allowed us to dissect the role of lincRNAs within the circuitry of a cell.”

The researchers used genetic tools to inhibit more than 100 lincRNAs and found that the vast majority — more than 90 percent — had a significant impact on embryonic stem cells, indicating that the RNAs play a key role in the cells’ circuitry.

Embryonic stem cells can follow one of two main routes. They can either differentiate, becoming cells of a specific lineage such as blood cells or neurons, or they can stay in a pluripotent state, duplicating themselves without losing the ability to become any cell in the body. When the researchers turned off each lincRNA in turn, they found dozens that suppress genes that are important only in specific kinds of cells. They also found dozens of lincRNAs that cause the stem cells to exit the pluripotent state.

“It’s a balancing act,” said Guttman.

“To maintain the pluripotent state, you need to repress differentiation genes.”

The researchers also uncovered a critical clue about how lincRNAs carry out their important job. Through biochemical analysis, they found that lincRNAs physically interact with key proteins involved in influencing cell fate to coordinate their responses.

“The lincRNAs appear to play an organizing role, acting as a scaffold to assemble a diverse group of proteins into functional units,” said John Rinn, an author on the paper, an assistant professor at Harvard University and Medical School, and a senior associate member of the Broad Institute.

“lincRNAs are like team captains, bringing together the right players to get a job done.”

“By understanding how these interactions form, we may be able to engineer these RNAs to do what we want them to do,” said Guttman.

“This could make it possible to target key genes that are improperly regulated in disease.”

Aviv Regev, an author on the paper, a core member of the Broad Institute, and associate professor at MIT, sees the team’s approach to studying the lincRNAs as important for the field.

“Many people are interested in lincRNAs, but they need a comprehensive view of the whole collection of lincRNAs,” said Regev.

“The large-scale data and technology from this study will be useful for scientists worldwide in studying both lincRNAs as well as many other RNAs in the cell.”

This project marks a collaborative effort involving experts in embryonic stem cells and lincRNAs as well as computational biologists and researchers in the Broad’s RNAi Platform, which developed the tools needed to systematically silence lincRNAs. Other researchers who contributed to this work include Julie Donaghey, Bryce W. Carey, Manuel Garber, Jennifer K. Grenier, Glen Munson, Geneva Young, Anne Bergstrom Lucas, Robert Ach, Xiaoping Yang, Ido Amit, Alexander Meissner, and David E. Root. This work was funded by the National Human Genome Research Institute, the Richard Merkin Foundation for Stem Cell Research at the Broad Institute, and funds from the Broad Institute of MIT and Harvard.

Source: Broad Communications

Contact: Haley Bridger

Reference:

lincRNAs act in the circuitry controlling pluripotency and differentiation
Mitchell Guttman, Julie Donaghey, Bryce W. Carey, Manuel Garber, Jennifer K. Grenier, Glen Munson, Geneva Young, Anne Bergstrom Lucas, Robert Ach, Laurakay Bruhn, Xiaoping Yang, Ido Amit, Alexander Meissner, Aviv Regev, John L. Rinn, David E. Root & Eric S. Lander
Nature. August 28, 2011 DOI: 10.1038/nature10398

See also:

LincRNAs Serve as Genetic Air-traffic Controllers
CellNEWS - Tuesday, 14 July 2009
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ScienceLive Chat about Stem Cell Future

ScienceLive Chat about Stem Cell Future
Thursday, 04 August 2011

Today, Thursday at 3 PM EDT, ScienceLive will be running a live chat on the future of stem cell research. Our staff writer Jocelyn Kaiser, will be moderating, and she'll have Hank Greely and Amander Clark on as science guests.

This chat is part of a new venture for us, called ScienceLive, where we bring our readers in touch with prominent scientists on a weekly basis so they can ask questions on the hottest topics in science.

Follow it here:


Source: Science
Contact: Yasmin Ogale, Assistant Producer, ScienceLive
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For more on stem cells and cloning, go to CellNEWS at
http://cellnews-blog.blogspot.com/

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