In vivo CRISPR screening reveals epigenetic regulators of hepatobiliary plasticity

Following prolonged liver injury, a small fraction of hepatocytes undergoes reprogramming to become cholangiocytes or biliary epithelial cells (BECs). This physiological process involves chromatin and transcriptional remodeling, but the epigenetic mediators are largely unknown. Here, we exploited a lineage-traced model of liver injury to investigate the role of histone post-translational modification in biliary reprogramming. Using mass spectrometry, we defined the repertoire of histone marks that are globally altered in quantity during reprogramming. Next, applying an in vivo CRISPR screening approach, we identified seven histone-modifying enzymes that alter the efficiency of hepatobiliary reprogramming. Among these, the histone methyltransferase and demethylase <i>Nsd1</i> and <i>Kdm2a</i> were found to have reciprocal effects on H3K36 methylation that regulated the early and late stages of reprogramming, respectively. Although loss of <i>Nsd1</i> and <i>Kdm2a</i> affected reprogramming efficiency, cells ultimately acquired the same transcriptomic states. These findings reveal that multiple chromatin regulators exert dynamic and complementary activities to achieve robust cell fate switching, serving as a model for the cell identity changes that occur in various forms of physiological metaplasia or reprogramming.