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Victoria A. Swiss
Bachelor of Arts, 2002
Rutgers, the State University of New Jersey
Thesis Advisor: Patrizia Casaccia-Bonnefil, MD, PhD
Tuesday, April 27, 2010
Oligodendrocytes are the myelin forming cells of the central nervous system. They derive from oligodendrocyte progenitor cells (OPCs) exit the cell cycle and initiate a complex transcriptional program of differentiation associated with chromatin compaction. Previous studies have characterized the post-translational modifications occurring on nucleosomal histones during OPC differentiation. These changes were dependent on the activity of histone deacetylases (HDACs), but the molecules linking cell cycle exit to chromatin changes and activation of the transcriptional program of differentiation remain undefined. This thesis tests the hypothesis that cell cycle regulators (i.e. E2Fs) modulate the expression of chromatin modifiers which orchestrate the transcriptional program of OPC differentiation.
Using a novel algorithm to interrogate the oligodendrocyte transcriptome, we first identified clusters of co-expressed genes and noticed that genes within each cluster had similar biological functions. We then focused our analysis on a cluster enriched for genes encoding cell cycle and chromatin regulators (e.g. Uhrf1 and H2a.z). The promoters of these genes were highly enriched in binding sites for E2F transcription factors. The expression patterns of E2f family members during the time course of OPC differentiation revealed a switch in the predominant family members. Chromatin immunoprecipitation analysis showed that E2F1 and E2F4 family members co-regulate the expression of Uhrf1 and H2a.z by sequential binding to the same promoter site during OPC differentiation. We measured high levels of Uhrf1 and H2A.z in OPC that were unable to differentiate, after siRNA-mediated silencing of E2f4. Finally, we showed that both UHRF1 and H2A.z were bound to the promoter of the late expressed myelin gene Mog in OPCs, but not in myelin expressing cells. We conclude that E2F transcription factors act as critical mediators of both cell cycle control and oligodendrocyte progenitor differentiation by regulating the expression of chromatin regulators.