Cardiac diseases are one of the leading causes of mortality in the western world. However, the molecular mechanisms responsible for these malformations or dysfunction remain poorly characterized. We have used the B type natriuretic peptide (BNP) as a marker to identify novel transcriptional pathways that regulate cardiac gene expression. Functional analysis of the BNP promoter had previously led to the identification of positive cis-regulatory elements and the isolation of the GATA-4 protein, which is an important trans-activator of several cardiac genes. The present study demonstrates that cell specific transcription from the BNP promoter is dependent on a dominant silencer activity in the distal upstream regulatory region, which serves to restrict its ectopic expression both, in vitro and in vivo. We have identified two distinct repressor domains R1 and R2 and show that while both repressor domains contribute additively to silencing of the native promoter, R2 alone is sufficient to repress the BNP promoter in heterologous cells. R2 is conserved across species and displays significant homology to a neuron restrictive silencer element (NRSE). We demonstrate sequence specific DNA binding activity on R2 that is present in a variety of non cardiac cells where the gene is repressed, but absent in cardiomyocytes, reiterating that repression is an important mechanism in the transcriptional regulation of BNP. / We have also investigated the potential role of cardiac enriched (GATA-4) and ubiquitous factors in regulation of BNP. We report that YY1, a known transcriptional repressor of muscle gene activity, is a positive regulator of BNP, and that it can synergise with the cardiac subgroup of GATA proteins (GATA-4 and GATA-6) to augment transcription. Collectively this work demonstrates that tissue restricted expression of BNP in vivo, is a result from the combinatorial interactions of both positive and negative factors, which include on the one hand, the GATA proteins that can activate the promoterin cardiac cells in conjunction with a variety of cell restricted and ubiquitous factors such as YY1 and on the other hand, repressor(s) that restrict its expression in non cardiac cells. / Our results are among the first to clearly demonstrate the in vivo importance of repressors in cardiac specific transcription, and emphasize how transcriptional diversity can be created by a limited set of transcription factors.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36546 |
| Date | January 1999 |
| Creators | Bhalla, Suparna S. |
| Contributors | Nemer, Mona (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Experimental Medicine.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001754111, proquestno: NQ64516, Theses scanned by UMI/ProQuest. |
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