TET1 displays catalytic and non-catalytic functions in the adult mouse cortex

TET1/2/3 dioxygenases iteratively demethylate 5-methylcytosine, beginning with the formation of 5-hydroxymethylcytosine (5hmC). The post-mitotic brain maintains higher levels of 5hmC than most peripheral tissues, and TET1 ablation studies have underscored the critical role of TET1 in brain physiology. However, deletion of <i>Tet1</i> precludes the disentangling of the catalytic and non-catalytic functions of TET1. Here, we dissect these functions of TET1 by comparing adult cortex of <i>Tet1</i> wildtype (<i>Tet1</i> WT), a novel <i>Tet1</i> catalytically dead mutant (<i>Tet1</i> HxD), and <i>Tet1</i> knockout (<i>Tet1</i> KO) mice. Using DNA methylation array, we uncover that <i>Tet1</i> HxD and KO mutations perturb the methylation status of distinct subsets of CpG sites. Gene ontology (GO) analysis on specific differential 5hmC regions indicates that TET1’s catalytic activity is linked to neuronal-specific functions. RNA-Seq further shows that <i>Tet1</i> mutations predominantly impact the genes that are associated with alternative splicing. Lastly, we performed High-performance Liquid Chromatography Mass-Spectrometry lipidomics on WT and mutant cortices and uncover accumulation of lysophospholipids lysophosphatidylethanolamine and lysophosphatidylcholine in <i>Tet1</i> HxD cortex. In summary, we show that <i>Tet1</i> HxD does not completely phenocopy <i>Tet1</i> KO, providing evidence that TET1 modulates distinct cortical functions through its catalytic and non-catalytic roles.