DNMT3L enables accumulation and inheritance of epimutations in transgenic Drosophila

DNMT3L interacts with Piwi and modulates the expression of piRNAs in transgenic Drosophila

Aim: To explore the role of Piwi protein and piRNAs in DNMT3L-mediated epigenetic inheritance. Materials & methods: Transgenic Drosophila were used to examine the effect of ectopically expressed DNMT3L on the profile of piRNAs by sequencing of small RNAs. Results & conclusion: Our previous work showed accumulation and inheritance of epimutations across multiple generations in transgenic DNMT3L Drosophila. Here, we show interaction of DNMT3L with Piwi and a significant alteration in the piRNA profile across multiple generations in transgenic Drosophila. In the light of its interaction with histone H1, we propose that in addition to its role of modulating core histone modifications, DNMT3L allows for inheritance of epigenetic information through its collaboration with Piwi, piRNAs and histone H1.

DNMT3L promotes neural differentiation by enhancing STAT1 and STAT3 phosphorylation independent of DNA methylation

Previously, we reported global hypermethylation in DS might be attributed to the overexpression of HSA21 gene DNMT3L, which can enhance DNMT3A and DNMT3B activities in DNA methylation. To test this hypothesis, we compared the DNA methylation and RNA expression profiles of early-differentiated human neuroprogenitors with and without DNMT3L overexpression. We found DNMT3L overexpression only moderately increased the DNA methylation of limited genes, yet significantly altered global RNA expression of genes involved in neural differentiation. We further found that DNMT3L bound STAT1 or STAT3, and increased its phosphorylation and nuclear translocation, which in turn activated the expression of transcription factors including HES3, ASCL1, NEUROD2 and NEUROG2 and CDK inhibitor CDKN1A, which promoted cell cycle exit and neural differentiation. This phenomenon was also confirmed in Dnmt3l conditional knockin mice, which could be rescued by STAT1 and STAT3 phosphorylation inhibitors (Fludarabine and SH-4-54) but not DNA methylation inhibitor (Decitabine). These results suggest that DNMT3L play an important role during neurodevelopment independent of DNA methylation, which may contribute to the abnormal phenotypes observed in Down syndrome cortex.

Drosophila DNA/RNA methyltransferase contributes to robust host defense in aging animals by regulating sphingolipid metabolism

Drosophila methyltransferase (Mt2) has been implicated in the methylation of both DNA and tRNA. In this study, we demonstrate that loss of Mt2 activity leads to an age-dependent decline of immune function in the adult fly. A newly eclosed adult has mild immune defects that are exacerbated in a 15 day old Mt2^-/- fly. The age-dependent effects appear to be systemic, including disturbances in lipid metabolism, changes in cell shape of hemocytes and significant fold-changes in levels of transcripts related to host defense. Lipid imbalance, as measured by quantitative lipidomics, correlates with immune dysfunction, with high levels of immunomodulatory lipids, sphingosine-1-phosphate (S1P) and ceramides, along with low levels of storage lipids. Activity assays on fly lysates confirm the age-dependent increase in S1P and concomitant reduction of S1P lyase activity. We hypothesize that Mt2 functions to regulate genetic loci such as S1P lyase and this regulation is essential for robust host defense as the animal ages. Our study uncovers novel links between age--dependent Mt2 function, innate immune response and lipid homeostasis.