Selective demethylation of two CpG sites causes postnatal activation of the Dao gene and consequent removal of D-serine within the mouse cerebellum
CLINICAL EPIGENETICS
Authors: Cuomo, Mariella; Keller, Simona; Punzo, Daniela; Nuzzo, Tommaso; Affinito, Ornella; Coretti, Lorena; Carella, Massimo; de Rosa, Valeria; Florio, Ermanno; Boscia, Francesca; Avvedimento, Vittorio Enrico; Cocozza, Sergio; Errico, Francesco; Usiello, Alessandro; Chiariotti, Lorenzo
Abstract
Background: Programmed epigenetic modifications occurring at early postnatal brain developmental stages may have a long-lasting impact on brain function and complex behavior throughout life. Notably, it is now emerging that several genes that undergo perinatal changes in DNA methylation are associated with neuropsychiatric disorders. In this context, we envisaged that epigenetic modifications during the perinatal period may potentially drive essential changes in the genes regulating brain levels of critical neuromodulators such as D-serine and D-aspartate. Dysfunction of this fine regulation may contribute to the genesis of schizophrenia or other mental disorders, in which altered levels of D-amino acids are found. We recently demonstrated that Ddo, the D-aspartate degradation gene, is actively demethylated to ultimately reduce D-aspartate levels. However, the role of epigenetics as a mechanism driving the regulation of appropriate D-ser levels during brain development has been poorly investigated to date. Methods: We performed comprehensive ultradeep DNA methylation and hydroxymethylation profiling along with mRNA expression and HPLC-based D-amino acids level analyses of genes controlling the mammalian brain levels of D-serine and D-aspartate. DNA methylation changes occurring in specific cerebellar cell types were also investigated. We conducted high coverage targeted bisulfite sequencing by next-generation sequencing and single-molecule bioinformatic analysis. Results: We report consistent spatiotemporal modifications occurring at the Dao gene during neonatal development in a specific brain region (the cerebellum) and within specific cell types (astrocytes) for the first time. Dynamic demethylation at two specific CpG sites located just downstream of the transcription start site was sufficient to strongly activate the Dao gene, ultimately promoting the complete physiological degradation of cerebellar D-serine a few days after mouse birth. High amount of 5'-hydroxymethylcytosine, exclusively detected at relevant CpG sites, strongly evoked the occurrence of an active demethylation process. Conclusion: The present investigation demonstrates that robust and selective demethylation of two CpG sites is associated with postnatal activation of the Dao gene and consequent removal of D-serine within the mouse cerebellum. A single-molecule methylation approach applied at the Dao locus promises to identify different cell-type compositions and functions in different brain areas and developmental stages.
Age and metallicity of a globular cluster in the dwarf spheroidal galaxy DDO 78
ASTRONOMY & ASTROPHYSICS
Authors: Sharina, ME; Sil'chenko, OK; Burenkov, AN
Abstract
We present the results of moderate resolution spectroscopy for a globular cluster in the M81 group dwarf spheroidal galaxy DDO 78. The DDO 78 globular cluster, 4 Milky Way globular clusters, spectroscopic and radial velocity standards were observed with the Long-slit spectrograph of the 6-m telescope (SAO RAS, Russia). Lick spectrophotometric indices were determined in the bandpasses adopted by Burstein et al. (1984). We have derived the mean metallicity of the globular cluster in DDO78 to be [Fe/H] = -1.6 +/- 0.1 dex by taking the weighted mean of metallicities obtained from the strength of several absorption features. We have estimated an age for the globular cluster of 9-12 Gyr similar to that found for the Galactic globular cluster NGC 362, which resembles the DDO 78 cluster in its chemical abundance and integrated spectrophotometric properties.