The following application is for supplementary funds to extend the studies of NS046789 on the role of ATP-dependent chromatin remodeling in neural development. ATP-dependent chromatin remodeling complexes are thought to regulate the mobility of nucleosomes allowing binding of sequence-specific transcription factors. In addition, they may be involved in the assembly of chromatin, the exchange of modified histones and also in controlling higher order chromatin structure or long distance looping of regulatory regions. There are about 30 genes encoding ATP-dependent chromatin regulators. Each of these ATPases appears to be part of large complexes of 10-20 subunits. A specialized ATP-dependent chromatin remodel complex is present in the nervous system and is essential for its development. Neural specific BAF complexes resemble SWI/SNF or SWR1 in yeast and have 11 subunits encoded by 21 genes. These subunits are combinatorially assembled giving rise to biologically specific functions in the way that letters are assembled into words to produce distinct meanings. In the transition from an ES cell to a neural progenitor, three subunits of the complex are selectively replaced. Additional development from a neural progenitor to a neuron leads to the removal of BAF53a and 45a from the complexes and the expression of BAF53b and BAF45b in neurons. The exchange of the BAF53a and 53b subunits appears to occur within a few hours of mitotic exit. Deletion of subunits of the npBAF complex leads to depletion of neural stem cells and death of the mice at birth with a failure to breathe or move and a small brain. In contrast, deletion of the subunits of the nBAF complexes leads to a normal size brain but a failure of dendritic development and death about 24 hours after birth due to a failure to nurse. We hope to use funds from this supplemental application to define the genome-wide distribution of the binding sites for BAF complexes in neurons and neural progenitors. Once these sites are established, we will determine the consequences of deletion of Brg and other subunits of the npBAF and nBAF complexes for local histone modifications, nucleosome positioning and accessibility to DNA binding transcription factors. Bioinformatic analysis of this data will yield mechanistic insights into the way that ATP-dependent chromatin remodeling interfaces with other pathways essential for the development of the nervous system.
One of the major challenges of modern biology and medicine is to repair damaged or diseased tissues. Avenues to accomplish this have grown from an understanding of the fundamental processes controlling the development of the embryo. One of these processes is the control of accessibility of our genetic material to regulatory mechanisms that allow an orderly use of genes to make tissues and organs such as the heart, lungs, immune system and brain. We hope to understand how the accessibility of genetic material is controlled during the formation of the brain and how it differs from other tissues. Our studies might provide new avenues for the production of tissues and cells for regeneration of diseased or damaged tissues.
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