Perturbations of the complex intrinsic and extrinsic factors that contribute to cellular differentiation can have many consequences ranging from dedifferentiation to cell death. The overall objective of my research is to investigate the factors that contribute to the maintenance of mature midbrain neurons and glia. In order to address this objective, I first carried out a detailed immunocytochemical analysis to demonstrate that histone deacetylase inhibitor (HDACI) treatment of differentiated midbrain neurons in culture results in an overall destabilization of neuronal phenotype, which leads to caspase-independent cell death. GFAP positive astrocytes are refractory to the effects of HDACI treatment, suggesting that inhibition of HDACs has differential effects on neurons and glia. HDACI treatment alone was not sufficient to induce neuronal dedifferentiation as evidenced by RT-PCR analysis of stem/progenitor markers, and recovery experiments. Finally, I demonstrate that cortical neurons do not undergo cell death in response to HDACI treatment, suggesting that there may be microenvironmental factors that promote the susceptibility of midbrain neurons to the neurotoxic effects of HDACI. In the second part of this thesis I determined the molecular mechanism that was at least partly responsible for the effects of HDACI treatment on midbrain neurons. Gene expression profiling of HDACI treated midbrain cultures revealed a strong down-regulation of immune related factors. This observation is supported by the loss of microglia in HDACI treated midbrain cultures. I also provide evidence that Toll-like receptor (TLR) signaling, likely through the activation of Interleukin-6 (IL-6) expression, mediates HDAC-dependent neuronal survival. These data provide new evidence that the neuroimmune system is an extrinsic regulator for the homeostasis and survival of neurons.

Long terminal repeat (LTR) retrotransposons account for approximately 10% of mouse and 8% of human genomes and may play a role in modifying gene expression. Many species harbor retrotransposon families encompassing both autonomous and non-autonomous members. Specifically, the mouse Early Transposon (ETn) family members lack all retroviral genes but are transcriptionally and retrotranspositionally active, causing over 20 known insertional germline mutations. ETns owe their retrotransposition potential to proteins encoded by structurally intact MusD retrotransposons with whom they share LTRs. ETn elements are transcribed at a much higher level than MusD retrotransposons in embryos and undifferentiated cells, suggesting their evasion of host restriction mechanisms. However, mechanisms responsible for the replicative success of non-autonomous retrotransposon subfamilies over their coding-competent relatives are poorly understood. In the first stage of my research, I analyzed regulatory sequences in an ETn LTR responsible for its high promoter activity in the undifferentiated cell line P19. I found that three GC-boxes that may function as Sp1/Sp3 binding sites act synergistically and are indispensable for undifferentiated cell-specific promoter activity of the LTR. Sp1 binding partners may be responsible for the restricted ETn expression. Moreover, I have shown that unlike many retroviruses, ETn elements possess multiple transcription initiation sites and that they have amplified via intracellular retrotransposition in the P19 teratocarcinoma cell line. In the next step of my research, I performed analysis of epigenetic mechanisms as a means of ERV suppression. Specifically, I showed that in embryonic stem cells, autonomous MusD retrotransposons are epigenetically suppressed to a greater degree than non-autonomous ETn retrotransposons, illustrated by a higher level of DNA methylation and a lower level of active histone modifications. I hypothesize that MusD elements may be silenced by DNA methylation and repressive chromatin spreading into the LTR from the CpG-rich internal retroviral sequence absent in ETn elements. I propose that internal structure largely devoid of high CG content enables ETn elements to evade host-imposed transcriptional repression, contributing to their high mutagenic activity in the mouse germline.

University, Diss., 2006--Frankfurt (Main). / Zsfassung in engl. und dt. Sprache.

Thesis (Ph.D.). / Written for the Dept. of Pharmacology and Therapeutics. Title from title page of PDF (viewed 2008/05/09). Includes bibliographical references.

Zugl.: Berlin, Freie Univ., Diss., 2007 u.d.T.: Fischer, Jenny J. Regulatory networks of gene expression in heart and skeletal muscle cells on the level of histone modifications and transcription factors / Hergestellt on demand

Thesis (Ph.D.)--University of Alabama at Birmingham, 2008. / Title from first page of PDF file (viewed on June 24, 2009). Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xv, 219 p.; also includes graphics (some col.) Includes bibliographical references (p. 147-173). Available online via OhioLINK's ETD Center

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 114-125). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.