Ten-eleven translocation (Tet) methylcytosine dioxygenases dependent viral DNA demethylation mediates in vivo hepatitis B virus (HBV) biosynthesis
Liver-specific ten-eleven translocation methylcytosine dioxygenases 2 and 3 (Tet2 plus Tet3)-deficient hepatitis B virus (HBV) transgenic mice fail to support viral biosynthesis.  The levels of viral transcription and replication intermediates are dramatically reduced.  Hepatitis B core antigen (HBcAg) is only observed in a very limited number of pericentral hepatocytes in a pattern that is similar to glutamate-ammonia ligase (Glul), a ?-catenin target gene.  HBV transcript abundance in Tet-deficient mice resembles that observed in wild-type neonatal mice.  Furthermore, the RNA levels of several ?-catenin target genes including Glul, Lhpp, Notun, Oat, Slc1a2 and Tbx3, in Tet-deficient mice was also similar to that observed in wild-type neonatal mice.  As HBV transcription is regulated by ?-catenin, these finding support the suggestion that neonatal Tet-deficiency might limit ?-catenin target gene expression, limiting viral biosynthesis.  Additionally, HBV transgene DNA displays increased 5-methylcytosine (5mC) frequency at CpG sequences consistent with neonatal Tet-deficiency being responsible for decreased developmental viral DNA demethylation mediated by 5mC oxidation to 5-hydroxymethylcytosine (5hmC), a process that might be responsible for the reduction in cellular ?-catenin target gene expression and viral transcription and replication. Overall design: Liver-specific Tet2-delete, Tet3-deleted and Tet2 plus Tet3-deleted HBV transgenic mice were generated and characterized to determine the role for Tet enzymes in the liver-specific demethylation of HBV transgene DNA which is associated with viral biosynthesis in this model of chronic infection.