Histone chaperone HIRA complex regulates retrotransposons in embryonic stem cells

Area of Science:

• Epigenetics and chromatin regulation
• Stem cell biology
• Genomics and molecular biology

Background:

• The Histone cell cycle regulator (HIRA) complex is a histone chaperone involved in H3.3 variant deposition.
• Its role in retrotransposon expression and cell fate determination in embryonic stem cells (ESCs) remains largely uncharacterized.

Purpose of the Study:

• To investigate the function of HIRA complex members in repressing retrotransposon expression in ESCs.
• To determine the involvement of the HIRA complex in cell fate determination and its mechanistic link to H3.3 deposition.

Main Methods:

• shRNA-mediated depletion of HIRA complex members in ESCs.
• RT-qPCR and RNA-seq for gene expression analysis.
• Chromatin immunoprecipitation (ChIP)-qPCR to assess H3.3 and HIRA member binding.
• Western blotting and co-immunoprecipitation for protein interactions and epigenetic modifications.

Main Results:

• Hira, Ubn2, and Ubn1 were identified as key repressors of the MERVL retrotransposon.
• Ubn2 and Hira target distinct retrotransposons and lncRNAs, influencing ESC pluripotency and differentiation pathways.
• Suppression of retrotransposons by Ubn2 and Hira involves regulating H3.3 deposition, leading to changes in repressive histone marks (H3K9me2/me3).

Conclusions:

• HIRA complex members exhibit distinct roles in controlling retrotransposon expression and cell fate in ESCs.
• The HIRA complex, through H3.3 deposition, plays a critical role in maintaining epigenetic stability and preventing aberrant cell state transitions.