Date of Graduation

1997

Document Type

Dissertation/Thesis

Abstract

Myelin associated glycoprotein (MAG) plays an important role in myelinogenesis, nerve plasticity and nerve regeneration. Hence, knowledge of how this gene is regulated may be essential for developing clinical strategies, e.g., to promote regeneration in the injured spinal cord. We employed the primer extension technique for mapping MAG gene transcription start sites. The analysis revealed 13 transcription start sites spanning 72 bp. No canonical TATA box and no known transcription initiator (Inr) sequences that position transcription complex in other TATA-less promoters were found. The structure of chromatin associated with the MAG gene was analyzed using progressive micrococcal nuclease digestion of isolated nuclei followed by an indirect end labeling technique. The analysis revealed a broad hypersensitivity region from approximately--1,600 bp to +600 bp that features nine hypersensitive sites (HS). These HS sites are formed within nucleosomal linkers without displacement of the nucleosomal core particles. The core promoter of the gene is located within one of the HS sites. The presence of nucleosomal core particles around the core promoter was confirmed by a genomic footprinting technique that combined mediated PCR (LMPCR). Furthermore, genomic footprinting revealed several putative protein binding sites as well as a hypersensitivity region within the approximately 80 bp long nucleosomal linker containing the core promoter region. The putative protein binding sites contain sequences that may be the targets for Sp1, AP2 and bHLH factors that are involved in assembly of initiation complexes on other TATA-less promoters. Although there were no apparent differences in the protein binding pattern between O2A progenitors and mature oligodendrocyte nuclei, a striking difference was observed in the binding between O2A progenitors and mature oligodendrocyte nuclear extracts tested in vitro by the mobility shift assay technique. The results suggest that the core promoter is controlled either by a different assortment of trans-factors expressed timely during oligodendrocyte differentiation that bind to the same DNA recognition sequences or by specific trans-factor expressed by mature oligodendrocytes that binds through protein-protein interaction to nucleoprotein complexes already formed in O2A progenitor nuclei.

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