Separately, we have been probing for SNVs at the DIXDC1 locus in human psychiatric patients (both in our own samples and in publicly-available sequence databases) and are testing these for functional differences in assays of Wnt/beta-catenin signaling and in assays based on phenotypic findings in this knock-out mouse model. We have also analyzed neurodevelopmental phenotypes in the brains of these animals and in cultured forebrain (hippocampal) neurons. We have tested the response of behavioral differences in these animals to psychopharmacological agents, including lithium. We have analyzed and compared behavior in littermates homozygous for the wild type Dixdc1 locus, heterozygous, or homozygous for the Dixdc1 KO allele. Methods: We have generated a Dixdc1 knock-out (KO) mouse line using traditional (homologous recombination) gene-targeting techniques. Recent human genetic studies have buttressed interest in this pathway by showing that loss-of-function mutations in the CHD8 gene, which up-regulate Wnt/beta-catenin pathway target genes, are a susceptibility factor in the autism spectrum disorders. Moreover, GSK3, the central kinase in the Wnt/beta-catenin pathway, is a pharmacological target of lithium at therapeutic doses. The Wnt/beta-catenin signaling pathway is broadly involved in neural development and for this reason has been considered a pontential pathogenic neurodevelopmental pathway in psychiatric illness. University of California at San Francisco, San Francisco, Californiaīackground: DIXDC1 encodes a scaffold protein enriched in neurons that physically interacts with the DISC1 protein implicated in major mental illness, as well as with the Dishevelled protein central to Wnt/beta-catenin intercellular signaling. A patent owned by MGH for the use of D-serine as a treatment for serious mental illness could yield royalties for Dr.
Future studies will determine whether D-serine administration, which reverses these abnormalities at the RNA and protein level, also normalizes the epigenetic perturbations.ĭisclosure: JTC served as a consultant for EnVivo and Abbvie in the last 2 years. The ChIP results suggest that reduced CREB binding contributes to the lower levels of BDNF, miR-132, and Arc that we previously observed in SR-/- mice. Finally, SR-/- mice have 80% less CREB binding to the synaptic activity response element (SARE) region of the Arc gene.Ĭonclusions: These data demonstrate that in vivo, NMDAR hypofunction caused by the selective removal of the NMDAR co-agonist, D-serine, leads to altered CREB binding on known activity-dependent genes. Using BDNF exon-specific primers, SR-/- mice have significantly less CREB binding at the BDNF I promoter, but not at the BDNF IV promoter. SR-/- mice have approximately 50% less CREB binding at the miR-132 gene than WT mice. Results: We first validated the ChIP kit for brain tissue using a positive control antibody and primers to ensure proper chromatin shearing. Melting temperature analysis was performed after every PCR to ensure accuracy. All of the primers were validated in previous publications. To determine the levels of CREB bound at each gene of interest, PCR primers were directed near the CRE sequence of each promoter. The crosslinks were reversed and the DNA was purified for analysis using qPCR (Sybr Green). The chromatin was incubated with a rabbit anti-CREB antibody (1:50 Cell Signaling Technologies) overnight at 4☌ on a rotisserie.
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Chromatin was digested using the SimpleChIP Plus Enzymatic Chromatin IP kit (Cell Signaling Technologies). Tissue samples were dissociated and then fixed with 1.5% paraformaldehyde. Methods: Wild-type (WT n=5-6) and SR-/- (n=5) mice were killed and their hippocampi were flash frozen on dry ice. In addition, these molecules are reduced in schizophrenia. We have previously demonstrated that serine racemase knockout (SR-/-) mice, which exhibit NMDAR hypofunction, also have reduced mRNA and protein levels of the aforementioned CREB-dependent genes in the hippocampus. The influx of calcium through N-methyl-D-aspartate receptors (NMDARs) is a well-defined mechanism that leads to the increased expression of CREB-dependent genes, including brain derived neurotrophic factor (BDNF), microRNA-132 (miR132), and activity-regulated cytoskeleton-associated protein (Arc). There are numerous signaling pathways by which information is transmitted from the cell membrane to the nucleus that in turn affects CREB binding to DNA. Harvard University, McLean Hospital, Belmont, Massachusettsīackground: cAMP-response-element-binding protein (CREB) is a ubiquitously expressed transcription factor in the brain that regulates neuroplasticity by modulating gene expression.
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