Investigating the role of USP22 in reprogramming
Somatic cells can be reprogrammed to induced pluripotent stem cells (iPSCs) by overexpressing OCT4, SOX2, KLF4 and MYC. Although this cell fate transition is a slow and inefficient process, inhibiting several epigenetic barriers has shown to facilitate it. A previously employed epigenetic focused CRISPR-Cas9-mediated knockout screen during reprogramming uncovered novel human somatic cell reprogramming barriers. Here, I showed that USP22, target for gRNAs that were enriched in iPSCs from the screen, is a barrier for reprogramming and its loss is compatible with iPSC generation. Overexpressing wild-type or deubiquitinase mutant (C185A) USP22 in knockout background could rescue the phenotype. Additionally, knocking out other SAGA deubiquitinase subunits, ENY2 and ATXN7L3 did not increase the reprogramming efficiency. Mechanistically, we showed that USP22 loss upregulates an important pluripotency-related transcription factor, SOX2, expression even as early as 3 days after OSKM expression. We hypothesized that USP22 downregulates pluripotency-related gene expression during reprogramming independent from its SAGA integration and deubiquitinase activity. To address this, I will repeat rescuing USP22 knockout phenotype in reprogramming by overexpressing mutant versions of USP22 including K129R (acetyl inhibited) and HHAA (deubiqutinase). Additionally, I will check the expression of pluripotency-related genes at early time points of reprogramming upon USP22 knockout by transcriptome profiling. Lastly, I will generate USP22 knockout iPSC lines to force them to differentiation to observe if they have any problem with pluripotency exit. This work will establish a mechanistic understanding for the role USP22 play on both human somatic cell reprogramming, pluripotency and differentiation. Overall design: We performed gene expression profiling analysis using data obtained from RNA-seq of 4 samples generated as independent duplicates from 2 different samples.