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Title: Transcriptional regulation of the aggrecan gene
Author: Li, I. M.
ISNI:       0000 0004 6425 1183
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2016
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Aggrecan is a large- aggregating proteoglycan that is essential for the function of articular cartilage. A loss of aggrecan is one of the major event in osteoarthritis, a debilitating and degenerative joint disease. To understand how a gene is lost and what fails to prevent transcription in disease state, an understanding of the bases of transcription must first be sought. Transcription is the first step in gene regulation and the chromatin plays an important role in blocking or allowing transcription to occur. Enhancers are non-coding DNA sequences that allow the binding of proteins, such as transcription factors that drive transcription irrespective of distance or orientation. Enhancers are marked by histone modifications that distinguish them from promoters and divide them into poised or active and are generally highly evolutionary conserved. Using publically available data on histone modifications found on ENCODE and transgenic mice this study has added to the understanding of the transcriptional regulation of aggrecan along with the known enhancer at -10kb. 3 intergenic regions, -35kb, -65kb and -87kb and one intronic (+26kb) from the transcription start site of aggrecan expresses primarily in the chondrocytes at E15.5. The -87kb enhancer marks chondrocytes that commit to an articular cartilage fate, and is strongly active in adult mice. The -65kb appears developmentally active, marking hypertrophic chondrocytes. The -35kb and +26kb are expressed in all chondrocytes at E15.5 mice and the -35kb is active in adult tissue. These enhancers bind to Sox9 and a loss of Sox9 in the -35kb enhancer shifts the expression from chondrocytes to fibroblast or perichondrium cells. These enhancers may play a role in response to diseases such as OA, as when these enhancers are transfected into differentiated murine ADTC5 cells and treated with Il-1β or hOSM there is a reduced level of expression from the -87kb element and an increase expression of the -65kb in response to Il-1β. A highly conserved intronic sequences (+55kb) was identified that does not express in chondrocytes, rather in kidney and lungs and may play a role outside of aggrecan gene regulation. Using the Acan promoter and the -35kb enhancer a cartilage-specific Cre recombinase line was generated providing a tool to explore the pathogenesis of cartilage genes in disease such as OA or in lineage tracing.
Supervisor: Bou-Gharios, G. ; Clegg, P. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral