A chromatin-focused CRISPR screen identifies USP22 as a barrier to somatic cell reprogramming

Area of Science:

• Stem Cell Biology
• Epigenetics
• Gene Regulation

Background:

• Cell-autonomous barriers hinder the efficient generation of induced pluripotent stem cells (iPSCs) from somatic cells.
• The precise molecular mechanisms underlying these barriers are not fully understood.

Purpose of the Study:

• To identify key factors that act as cell-autonomous barriers to human iPSC derivation.
• To investigate the role of Ubiquitin-specific peptidase 22 (USP22) in somatic cell identity and pluripotency.
• To explore USP22 as a potential therapeutic target for enhancing reprogramming efficiency.

Main Methods:

• A focused CRISPR-Cas9 genetic screen was employed to identify barriers to iPSC reprogramming.
• Module-specific knockouts and genetic rescue experiments were performed to dissect USP22's function.
• Gene expression analysis was conducted to assess changes in somatic and pluripotency-associated genes.

Main Results:

• Ubiquitin-specific peptidase 22 (USP22) was identified as a significant chromatin-based barrier to iPSC derivation.
• Suppression of USP22 markedly enhanced reprogramming efficiency, independent of its deubiquitinase activity or SAGA complex association.
• USP22 loss downregulated fibroblast-specific genes and upregulated pluripotency genes (e.g., DNMT3L, LIN28A, SOX2, GDF3), promoting reprogramming under both primed and naïve conditions.

Conclusions:

• USP22 plays a critical, previously unrecognized role in maintaining somatic cell identity and suppressing pluripotency.
• Targeting USP22 presents a promising strategy to overcome reprogramming barriers and improve the efficiency of generating iPSCs.
• These findings contribute to a deeper understanding of the epigenetic regulation governing cellular reprogramming.