A ‘tête-à-tête’ with TET Mammals control gene expression using various epigenetic mechanisms. EU funded researchers investigated the role of a family of DNA modifying proteins in pluripotency. Industrial Technologies Fundamental Research Health © anyaivanova, Shutterstock Recently, scientists discovered that the Ten-Eleven-Translocation (TET) family of dioxygenases are involved in DNA demethylation and pluripotency. These proteins convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxycytosine (5caC) in DNA, and are the only known mammalian enzymes that can initiate a complete pathway of active DNA demethylation. Therefore, they are key in many biological processes such as zygotic epigenetic reprogramming, pluripotent stem cell differentiation, haematopoiesis and leukaemia. The EPIPLUS (A novel epigenetic modification in pluripotent stem cells) project aimed to uncover the poorly understood underlying mechanisms of action of these enzymesin early mammalian development. The EPIPLUS team characterised the promoter and enhancer domains in the DNA involved in Tet1 and Tet2 regulation in mouse embryonic stem cells. They were able to identify the developmental stage- and tissue-specific expression patterns of Tet1 and Tet2. More importantly, their experiments revealed that Tet1-mediated hydroxymethylation is a key process during embryonic development. Researchers generated transgenic mouse reporter strains for cell state-specific expression of Tet1 and crossed them to obtain double-reporter transgenic mouse models. They studied cell reprogramming kinetics in these mouse embryonic fibroblasts by tracking the master pluripotency factor Oct4. They noted that cells were successfully reprogrammed towards induced pluripotent stem cell (iPSC) fate via an ordered sequential activation of enhancers regulating both Oct4 and Tet1. Using reporter patterns, further analyses of stage-specific reprogramming intermediates is ongoing to determine the critical epigenetic changes required for obtaining fully naive pluripotency in iPSCs. EPIPLUS outcomes should help scientists create an epigenetic blueprint of mammalian embryonic development that will also aid in manipulating cell fate in vitro. Given that deregulated TET activity is implicated in developmental disorders and cancer, researchers could use the knowledge generated from this study in disease modelling, toxicology studies and cellular replacement therapies. Keywords TET, demethylation, pluripotency, epigenetic reprogramming, EPIPLUS, Oct4, iPSC
