Downregulation of ten-eleven translocation-2 triggers epithelial differentiation during organogenesis

DNA methylation of cytosine bases is a major epigenetic modification that regulates gene expression and vertebrate development. The ten-eleven translocation (TET) enzymes oxidize 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), and active DNA demethylation influences gene expression specific to each developmental stage, although recent reports have shown that TET also has a non-catalytic function. In fetal mice, the epithelium in the submandibular gland (SMG) buds as a derivative of the oral cavity at embryonic day 11 (E11) and, by E15, it begins to differentiate into the salivary epithelium, which expresses water-channel aquaporin 5 (AQP5). The functional differentiation of the SMG epithelium can be regulated epigenetically, but how TET enzymes contribute is largely unknown. Here, we used several techniques, including hydroxymethylated DNA immunoprecipitation qPCR and histological analysis, to examine the changes in 5hmC levels and AQP5 and TET expression during SMG development. We found that 5hmC levels and AQP5 expression increased in the E15 SMG epithelium, while TET2 expression in the terminal buds decreased at E15. In agreement with the in vivo observations, Tet2 inhibition ex vivo led to the upregulation of AQP5 expression in terminal buds of the SMG epithelium. These results suggest that the downregulation of TET2 expression at E15 is a critical epigenetic event that establishes the epithelial fate for functional SMGs during development.