Citrullination regulates pluripotency and histone H1 binding to chromatin

Area of Science:

• Biochemistry and Molecular Biology
• Stem Cell Biology
• Epigenetics

Background:

• Citrullination, the conversion of arginine to citrulline by peptidylarginine deiminases (PADIs), alters protein charge and function.
• PADIs are implicated in various diseases, but their physiological roles, particularly in pluripotency, are unclear.
• PADI4, a nuclear PADI, decondenses chromatin in innate immunity.

Purpose of the Study:

• To investigate the role of PADI4 in mouse pluripotency and cellular reprogramming.
• To identify novel PADI4 substrates involved in chromatin regulation.
• To elucidate the mechanism by which PADI4 influences chromatin structure.

Main Methods:

• Analysis of Padi4 expression and activity during pluripotency and reprogramming.
• Functional studies involving Padi4 inhibition in mouse embryos and reprogramming systems.
• Unbiased proteomic analysis to identify PADI4 targets.
• Chromatin immunoprecipitation and biochemical assays to validate substrate interactions.

Main Results:

• Padi4 expression and activity are induced in pluripotent and reprogramming mouse cells.
• Padi4 is part of the pluripotency transcriptional network, activating key stem cell genes.
• Inhibition of Padi4 reduces pluripotency and reprogramming efficiency.
• Linker histone H1 variants are identified as novel PADI4 substrates.
• Citrullination of histone H1 displaces it from chromatin, leading to decondensation.

Conclusions:

• PADI4 plays a critical role in regulating ground-state pluripotency and reprogramming.
• Histone H1 citrullination by PADI4 is a key mechanism for chromatin decondensation.
• This study uncovers a novel function of citrullination in controlling stem cell states.