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Research Interest
DNA methylation in brain development and function, and during neuronal differentiation of embryonic stem (ES) cells in vitro
Our current research focuses on understanding epigenetic mechanisms that regulate neural cell differentiation and adult brain function. We utilize molecular and genetic approaches to investigating how DNA cytosine methylation and its associated components, which include methyl-CpG binding proteins and histone modification enzymes, regulate neural gene expression, cell-lineage differentiation, and neural plasticity in development and aging.
1). DNA methylation in neuronal gene regulation and cell differentiation: Abnormal DNA methylation has been associated with several human mental retardation disorders, including fragile-X, ICF, and Rett Syndromes. To study the methylation function in the brain, we have used the Cre/loxP conditional gene knockout method to produce transgenic mice that are deficient of the DNA methyltransferase I (Dnmt1) exclusively in the central nervous system (CNS) (J. Neuroscience 21:788-797). Dnmt1 deficiency results in DNA hypomethylation in CNS precursor cells and their progeny neuronal and glial cells. We found that DNA hypomethylation induces precocious astroglial cell differentiation in the CNS, suggesting that DNA methylation is a critical determinant in controlling the timing and magnitude of neural cell differentiation. Using DNA microarray technology, we found that a number of neural genes are deregulated in the hypomethylated CNS. We are currently defining the molecular mechanism by which DNA hypomethylation alters neuronal gene expression (Science 302: 890-893), cell survival, and lineage-differentiation in the CNS.
2). Epigenetic mechanisms underlying neuronal differentiation of embryonic stem (ES) cells in vitro: ES cells are pluripotent and can be induced to differentiate into multiple cell lineages in vitro. However, mechanisms underlying directed differentiation of ES cells are poorly understood. To examine whether cell lineage-specific differentiation of ES cells is regulated by epigenetic factors such as DNA methylation, we have established a culture system to induce sequential neuronal and glial differentiation with mouse and human ES cells. Because ES cell lines are particularly amenable to genetic manipulation, we can generate and utilize mutant ES cell lines to analyze the involvement of epigenetic factors in neural cell differentiation in vitro. We have found that mouse de novo DNA methyltransferases Dnmt3a and 3b are required for suppressing astroglial differentiation and silencing glial cell lineage genes during the early neurogenic phase of ES cell differentiation. Our short-term goal is to define the changes in DNA methylation and histone modifications during neuronal differentiation of ES cells. It is our hope that we can achieve high efficiency neuronal differentiation with mouse and human ES cells through genetic and/or pharmacological interventions of DNA methylation and chromatin modifications.
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