H3K9 methylation is a barrier during somatic cell reprogramming into iPSCs

Area of Science:

• Epigenetics
• Stem Cell Biology
• Cellular Reprogramming

Background:

• The stepwise induction of pluripotent stem cells (iPSCs) is not fully understood.
• Epigenetic modifications play a crucial role in cellular fate determination and reprogramming.

Purpose of the Study:

• To elucidate the epigenetic mechanisms governing the intermediate pre-iPSC state during reprogramming.
• To identify signaling pathways and epigenetic factors that control the transition from pre-iPSCs to fully reprogrammed iPSCs.

Main Methods:

• Generation and characterization of stable pre-iPSC lines.
• Analysis of histone modifications, specifically H3K9 methylation.
• Investigation of signaling pathways, including bone morphogenetic proteins (BMPs).
• Identification of H3K9 methyltransferases and demethylases involved in regulating pluripotency gene loci.

Main Results:

• Histone H3 lysine 9 (H3K9) methylation is identified as the primary epigenetic determinant of the pre-iPSC state.
• Pre-iPSCs exhibit pluripotency but lack core pluripotency network activation and are sensitive to vitamin C for conversion.
• Bone morphogenetic proteins (BMPs) in serum were found to arrest reprogramming at the pre-iPSC stage.
• H3K9 methyltransferases, downstream of BMPs, and their demethylases act as an epigenetic switch controlling pre-iPSC fate via H3K9 methylation at pluripotency loci.

Conclusions:

• Pre-iPSCs represent a stable epigenetic intermediate in the reprogramming process.
• The interplay between BMP signaling, H3K9 methylation/demethylation, and pluripotency gene regulation is critical for controlling cell fate reprogramming.