HBO1 is an epigenetic determinant of hepatocyte-to-ductal reprogramming

Spontaneous cellular reprogramming is rare, but has been observed in adult cells. This is most evident in the mammalian liver, where hepatocytes undergo physiological reprogramming to generate functional biliary epithelial cells (BECs) in response to injury. The underlying mechanisms driving this cell fate switch remain unclear, however. Here, we characterize epigenetic changes occurring during this transition at the single cell level, and show that reprogramming occurs synchronously and deterministically, though reprogrammed cells retain epigenetic hepatocyte memory. An in vivo CRISPR screen reveals the histone acetyltransferase-HBO1 functions as a critical barrier to hepatocyte reprogramming via acetylation of H3K14. HBO1 depletion accelerates BEC-specific chromatin remodeling and allows for the full resolution of the hepatocyte chromatin landscape. Mechanistically, HBO1 is recruited by the YAP to TEAD target sites to negatively its modulate chromatin-accessibility, DNA-binding, and transcriptional-output, thus acting as an epigenetic brake for YAP/TEAD function. Our work here delineates epigenetic trajectories of a physiological reprogramming process and identifies HBO1 as potential target for hepatocyte trans-differentiation therapeutic strategies.