Parathyroid hormone (PTH) and PTH-related peptide (PTHrP) stimulate signal transduction in target cells by binding to the same G protein-linked receptor (PTHR). The PTHR mediates PTH signaling in kidney and bone, and PTHrP binding to the receptor has been shown to be essential for normal endochondral bone formation in humans and mice. / Expression of the murine PTHR gene is controlled by two promoters that are regulated differently. Whereas the activity of the upstream promoter (P1) is mainly restricted to the kidney, where it provides the bulk of the gene transcription, the downstream promoter (P2) is more widely active. We characterized the upstream regulatory region of the human PTHR gene and showed that its organization is very similar to that of the mouse PTHR gene. RNase protection experiments revealed, however, that the homologue of the mouse renal-specific promoter PI, is only weakly active. This observation led us to identify and characterize a third promoter P3) that is responsible for the expression of more than 80% of human renal transcripts, but is apparently not active in mouse kidney. A study of the tissue distribution of the activity of P1, P2 and P3 showed that, while P2 and P3 are widely active, function of P1 is restricted to renal tissues. This study further revealed the existence of a shorter, differentially spliced variant of P2 derived transcripts. P1 and P3 were found to be developmentally regulated, as no activity was detected at mid-gestation. Hence, expression of the PTHR gene until this stage is driven solely by P2. Furthermore, the shorter P2-specific transcript observed in adult not detected in fetal tissues, suggesting that differential splicing of PTHR mRNA is developmentally regulated as well. / The observation that activity of PI and P3 is developmentally up-regulated, and the presence of P3 within a CpG island, prompted us to examine whether DNA methylation could play a role in regulating PTHR promoter function. Our results show that all three promoters are sensitive to methylation in vitro and that the methylation pattern of Pl is renal specific and is established well before the onset of PTHR gene expression. Our results suggest that while the transcriptional regulation of the PTIHR gene expression during development might be similar in mouse and human, expression in the adult is likely to be controlled by different mechanisms. / We also addressed the presence of structural alterations of the 5 ' regulatory region in patients with pseudohypoparathyroidism type Ib. Genomic southern blot analysis, as well as sequencing of the three upstream untranslated exons did not reveal any deletion or point mutation that could account for the kidney specific loss of PTH response observed in these patients.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.35677 |
| Date | January 1998 |
| Creators | Bettoun, Joan David. |
| Contributors | White, J. H. (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 (Department of Physiology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001651355, proquestno: NQ50114, Theses scanned by UMI/ProQuest. |
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