Multicellular organisms consist of hundreds of different cell types, each of which is characterized by a unique pattern of gene expression. Different cell types must stably maintain the transcriptional patterns that specify that cell type, yet have sufficient plasticity to allow the alterations in gene expression that are necessary for differentiation or responses to environmental changes. Establishment and maintenance of these diverse expression patterns is fundamentally important for cell identity and organismal survival, since aberrant gene expression in a single cell can lead to developmental abnormalities or cancer. We use mouse embryonic stem cells (ESCs) to study the molecular mechanisms that are used to regulate gene expression in mammalian cells. ESCs are pluripotent, with the ability to differentiate into every cell type that makes up the developing and adult organism. ESCs continue to self-renew, or indefinitely proliferate in the pluripotent state, when they are cultured under appropriate conditions. Several transcription factors, such as Oct4, Nanog, Sox2, Foxd3, and Stat3, are essential for self-renewal and pluripotency. While it is thought that regulation at the level of chromatin structure is also important in ESC self-renewal and pluripotency, the role of chromatin regulatory proteins in these processes remains more poorly understood. Here we propose to investigate the role of the Tip60-p400 histone acetyltransferase-chromatin remodeling complex in ESC self-renewal. Our preliminary results indicate that tip60-p400 cooperates with the pluripotency transcription factor Nanog to maintain the ESC-specific expression profile that promotes self-renewal and pluripotency. Our studies will focus on understanding the molecular nature of the functional interaction between the Tip60-p400 complex and Nanog. Finally, our preliminary results implicate a second chromatin remodeling complex, the Brg1-containing Swi/Snf complex in ESC self-renewal. We will also investigate the mechanisms by which this complex regulates the ESC-specific gene expression profile.
Embryonic stem cells can grow indefinitely as an established cell line, a process referred to as self-renewal. ESCs are highly proliferative in their undifferentiated state. In contrast, somatic stem cells, such as hematopoietic stem cells, grow more slowly than ESCs and do not expand without significant accompanying differentiation. ESCs are also pluripotent - they have the ability to differentiate into all cell types. Because of these properties, ESCs are regarded as a major potential source of material for stem cell therapies. However, the molecular mechanisms governing self-renewal and pluripotency are largely unknown. A better molecular understanding at the factors that induce and maintain the stem cell state ESCs is essential for moving towards the implementation of ESC-based therapies. We employ mouse ESCs to understand the role of chromatin regulatory proteins, which regulate gene expression by affecting the accessibility of the DNA template, in ESC self-renewal and pluripotency. These studies will have important impacts on the development of ESC lines for stem-cell based therapies.
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