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MacroH2A histone variants act as a barrier upon reprogramming towards pluripotency
Alexandre Gaspar-Maia1, Zulekha A Qadeer, Dan Hasson
1Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, 1425 Madison Avenue, New York, New York 10029, USA.
Nature Communications
|March 7, 2013
Summary
Macrohistone variants (macroH2A) create an epigenetic barrier to reprogramming somatic cells into induced pluripotent stem cells. Macrohistone variants cooperatively silence pluripotency genes, acting as a differentiation lock.
Area of Science:
- Epigenetics
- Stem Cell Biology
- Chromatin Biology
Background:
- Somatic cell reprogramming to induced pluripotency is crucial for regenerative medicine.
- The chromatin template presents epigenetic barriers to this process.
- Histone variants play significant roles in regulating gene expression and chromatin structure.
Purpose of the Study:
- To investigate the role of macrohistone variants (macroH2A) as epigenetic barriers to somatic cell reprogramming.
- To identify the specific macroH2A isoforms involved in blocking induced pluripotency.
- To elucidate the mechanism by which macroH2A isoforms silence pluripotency genes.
Main Methods:
- Generation and analysis of macroH2A double knockout (dKO) mouse embryonic fibroblasts.
- Manipulation of macroH2A isoform expression.
- Genomic analyses including ChIP-seq to assess histone modifications and gene occupancy.
- Assessment of reprogramming efficiency and pluripotency of derived cells.
- In vitro and in vivo differentiation assays.
Main Results:
- Macrohistone variants (macroH2A) act cooperatively to establish an epigenetic barrier to induced pluripotency.
- Macrohistone variant 2 (macroH2A2) is identified as the predominant barrier to reprogramming.
- Macrohistone variants, along with H3K27me3, co-occupy pluripotency genes in wild-type fibroblasts.
- Macrohistone isoforms are enriched at target genes of Utx, a K27me3 demethylase, which are reactivated early during reprogramming.
- Macrohistone variant deficient cells can be reprogrammed, and their differentiated cells retain the ability to revert to a stem-like state.
Conclusions:
- Macrohistone variants provide a redundant silencing mechanism or a terminal differentiation lock at key pluripotency genes.
- This epigenetic barrier imposed by macrohistone variants is critical for maintaining differentiated cell states and preventing inappropriate dedifferentiation.
- Understanding this barrier mechanism could inform strategies for enhancing reprogramming efficiency and controlling cell fate.
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