In the central nervous system, epigenetic modifications have been implicated in synaptic plasticity and neurological disorders such as Rett Syndrome and immunodeficiency centromeric region instability, facial anomalies syndrome. DNA methylation is an epigenetic modification whereby cytosine nucleotides are methylated by enzymes called DNA methyltransferases. The methylated cytosine is part of a cytosine-phosphate-guanine dinucleotide, usually, in regulatory regions of genes that causes transcriptional repression. We hypothesize that neuron degeneration can result from epigenetic modifications such as DNA methylation. We have studied the expression and localization of DNA methyltransferases in mouse CNS during development and have used in vitro and in vivo models of neuronal degeneration to study the role of DNA methylation in neuron cell death. We utilize DNA methyltransferases to characterize endogenous DNA methylation in rodents, manipulate DNA methylation in a motor neuron-like cell line called neuroblastoma/spinal cord-34, and assess DNA methylation in a murine model of motor neuron degeneration.;Our findings show that the different classes of DNA methyltransferases are differentially expressed in developing mouse brain and subcellular fractions of neuronal cells. In addition, DNA methyltransferases are activated when undifferentiated and differentiated motor neuron-like cells are induced to undergo apoptosis by a topoisomerase inhibitor, camptothecin. Our in vitro studies using cloned fusion proteins indicate that motor neuron-like cells are adversely affected by upregulation of one class of DNA methyltransferase, 3a; however, specific knockdown of DNA methyltransferases by siRNA blocked cytotoxicity. Additionally, when these motor neuron-like cells are subjected to DNA methyltransferase inhibitors, procainamide and RG108 prior to induction of apoptosis, there is a decrease in motor neuron degeneration. In our in vivo murine model of motor neuron degeneration, DNA methyltransferase immunoreactivity was highly selective for motor neurons by immunohistochemistry. Furthermore, these methyltransferases were differentially expressed on lesioned versus non-lesioned sides of lumbar spinal cord when observed by western blot. Our in vitro and in vivo analyses of DNA methylation in the central nervous system will facilitate future studies of elucidating the mechanisms by which DNA methyltransferases regulate neuronal cells and developing therapies to motor neuron diseases and possibly other neurodegenerative diseases.
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