Binding of MBD proteins to DNA blocks Tet1 function thereby modulating transcriptional noise.

Aberrant DNA methylation is a hallmark of various human disorders, indicating that the spatial and temporal regulation of methylation readers and modifiers is imperative for development and differentiation. In particular, the cross-regulation between 5-methylcytosine binders (MBD) and modifiers (Tet) has not been investigated. Here, we show that binding of Mecp2 and Mbd2 to DNA protects 5-methylcytosine from Tet1-mediated oxidation. The mechanism is not based on competition for 5-methylcytosine binding but on Mecp2 and Mbd2 directly restricting Tet1 access to DNA. We demonstrate that the efficiency of this process depends on the number of bound MBDs per DNA molecule. Accordingly, we find 5-hydroxymethylcytosine enriched at heterochromatin of Mecp2-deficient neurons of a mouse model for Rett syndrome and Tet1-induced reexpression of silenced major satellite repeats. These data unveil fundamental regulatory mechanisms of Tet enzymes and their potential pathophysiological role in Rett syndrome. Importantly, it suggests that Mecp2 and Mbd2 have an essential physiological role as guardians of the epigenome.

A Phase I Trial to Determine the Pharmacokinetics, Psychotropic Effects, and Safety Profile of a Novel Nanoparticle-Based Cannabinoid Spray for Oromucosal Delivery.

INTRODUCTION: A phase I, open-label clinical trial in healthy male subjects was conducted to assess the pharmacokinetic and safety profile of an oromucosal cannabinoid spray (AP701) containing a lipid-based nanoparticular drug formulation standardized to ∆-9-tetrahydrocannabinol (THC). METHODS: Twelve healthy male subjects received a single dose of AP701 (12 sprays) containing 3.96 mg THC. Plasma samples were drawn 10 min-30 h post dose for analysis of THC and the active metabolite 11-hydroxy-∆-9-THC (11-OH-THC). RESULTS: The single dose of the applied oromucosal cannabinoid spray AP701 (12 sprays, 3.96 mg THC) resulted in a mean maximum plasma concentration (Cmax) of 2.23 ng/mL (90% CI 1.22-3.24) and a mean overall exposure (area under the concentration-time curve from time 0 to last measurable concentration [AUC0-t]) of 7.74 h × ng/mL (90% CI 5.03-10.45) for THC. For the active metabolite 11-OH-THC, a Cmax of 2.09 mg/mL (90% CI 1.50-2.68) and AUC0-t of 10.4 h × ng/mL (90% CI 7.03-13.77) was found. The oromucosal cannabinoid spray AP701 caused only minor psychotropic effects despite the relatively high dosage applied by healthy subjects. No serious adverse effects occurred. Overall, the oromucosal cannabinoid spray AP701 was well tolerated. CONCLUSION: Compared to currently available drugs on the market, higher AUC values could be detected for the oromucosal cannabinoid spray AP701 despite administration of a lower dose. These comparatively higher blood levels caused only minor psychotropic adverse effects. The oromucosal cannabinoid spray AP701 was well tolerated at a single dose of 3.96 mg THC. The oromucosal administration may provide an easily applicable and titratable drug formulation with a high safety and tolerability profile.

Systematic analysis of the binding behaviour of UHRF1 towards different methyl- and carboxylcytosine modification patterns at CpG dyads.

The multi-domain protein UHRF1 is essential for DNA methylation maintenance and binds DNA via a base-flipping mechanism with a preference for hemi-methylated CpG sites. We investigated its binding to hemi- and symmetrically modified DNA containing either 5-methylcytosine (mC), 5-hydroxymethylcytosine (hmC), 5-formylcytosine (fC), or 5-carboxylcytosine (caC). Our experimental results indicate that UHRF1 binds symmetrically carboxylated and hybrid methylated/carboxylated CpG dyads in addition to its previously reported substrates. Complementary molecular dynamics simulations provide a possible mechanistic explanation of how the protein could differentiate between modification patterns. First, we observe different local binding modes in the nucleotide binding pocket as well as the protein's NKR finger. Second, both DNA modification sites are coupled through key residues within the NKR finger, suggesting a communication pathway affecting protein-DNA binding for carboxylcytosine modifications. Our results suggest a possible additional function of the hemi-methylation reader UHRF1 through binding of carboxylated CpG sites. This opens the possibility of new biological roles of UHRF1 beyond DNA methylation maintenance and of oxidised methylcytosine derivates in epigenetic regulation.

Two distinct modes of DNMT1 recruitment ensure stable maintenance DNA methylation.

Stable inheritance of DNA methylation is critical for maintaining differentiated phenotypes in multicellular organisms. We have recently identified dual mono-ubiquitylation of histone H3 (H3Ub2) by UHRF1 as an essential mechanism to recruit DNMT1 to chromatin. Here, we show that PCNA-associated factor 15 (PAF15) undergoes UHRF1-dependent dual mono-ubiquitylation (PAF15Ub2) on chromatin in a DNA replication-coupled manner. This event will, in turn, recruit DNMT1. During early S-phase, UHRF1 preferentially ubiquitylates PAF15, whereas H3Ub2 predominates during late S-phase. H3Ub2 is enhanced under PAF15 compromised conditions, suggesting that H3Ub2 serves as a backup for PAF15Ub2. In mouse ES cells, loss of PAF15Ub2 results in DNA hypomethylation at early replicating domains. Together, our results suggest that there are two distinct mechanisms underlying replication timing-dependent recruitment of DNMT1 through PAF15Ub2 and H3Ub2, both of which are prerequisite for high fidelity DNA methylation inheritance.

Recent evolution of a TET-controlled and DPPA3/STELLA-driven pathway of passive DNA demethylation in mammals.

Genome-wide DNA demethylation is a unique feature of mammalian development and naïve pluripotent stem cells. Here, we describe a recently evolved pathway in which global hypomethylation is achieved by the coupling of active and passive demethylation. TET activity is required, albeit indirectly, for global demethylation, which mostly occurs at sites devoid of TET binding. Instead, TET-mediated active demethylation is locus-specific and necessary for activating a subset of genes, including the naïve pluripotency and germline marker Dppa3 (Stella, Pgc7). DPPA3 in turn drives large-scale passive demethylation by directly binding and displacing UHRF1 from chromatin, thereby inhibiting maintenance DNA methylation. Although unique to mammals, we show that DPPA3 alone is capable of inducing global DNA demethylation in non-mammalian species (Xenopus and medaka) despite their evolutionary divergence from mammals more than 300 million years ago. Our findings suggest that the evolution of Dppa3 facilitated the emergence of global DNA demethylation in mammals.