The 9 PAX genes constitute a family of developmental transcriptional regulators characterized by a highly conserved "paired-box" domain. Mutations in 6 of the 9 PAX genes result in autosomal dominant congenital malformations in mice and in humans. PAX2 transcripts are detected in the CNS, throughout the genitourinary tract, eye and ear. In humans, mutations of PAX2 cause Renal-Coloboma Syndrome (RCS), a constellation of renal anomalies, eye defects and, less frequently, hearing loss and mild CNS manifestations. Homozygous PAX2 mutations in mice cause complete renal agenesis and perinatal death. PAX8 transcripts are found in the CNS, kidney and thyroid glands. PAX8 mutations cause congenital thyroid hypoplasia. No renal defects have been detected either in human or murine PAX8 mutants. / In spite of considerable information about PAX2 and PAX8 genes, their precise functions in development are poorly understood. This project was aimed at elucidating the functions of PAX2 and PAX8 in nephrogenesis and is subdivided into two parts: mutational screening of the PAX8 gene (Chapter 4) and delineation of the role of PAX2 in developing kidney (Chapters 5--7). The latter evolved into the major portion of this work. / Familial juvenile nephronophthisis (NPH1) is a rare disease characterized by multiple small cysts at the cortico-medullary junction and end-stage renal failure in pediatric populations. Because of its proximity to the disease locus, we considered PAX8 a candidate gene for NPH1. During analysis of PAX8 exons from patients, we identified a rare non-conservative polymorphic amino acid change, but found no causative mutations. Subsequently, other groups isolated the novel NPH1 gene. Following reports that PAX8 knockout mice have no obvious renal anomaly, we considered the possibility that PAX8 mutations might, nevertheless, affect proximal tubule function. In patients with thyroid hypoplasia and proven PAX8 mutations we found no aminoaciduria, indicating that haploinsufficiency for PAX8 does not alter tubular transport function. / In order to define PAX2 function in the two primordial cell lineages of developing kidney (induced metanephric mesenchyme and ureteric epithelium), we used both a cell culture approach and an in vivo PAX2 mutant mouse model (1Neu). We demonstrated that PAX2 plays a dual role. In mesenchymally-derived HEK293 cells expressing regulatable exogenous PAX2, we showed that PAX2 is responsible for expression of genes involved in differentiation of mesenchyme. Contrary to one published hypothesis, we found that PAX2 does not affect cell division. In ureteric epithelium, however, PAX2 plays a different role, serving as a survival factor, critical for sustaining the ureteric bud stem cell population. Attenuation of PAX2 dosage (1Neu mouse mutants or collecting duct cells transfected with an antisense PAX2 vector) results in increased apoptosis. We demonstrate that the primary renal defect in RCS is reduced nephron number associated with excessive apoptosis and simplified branching of the ureteric bud. We hypothesize that arborization of the uretric bud requires accumulation of sufficient stem cell mass to allow the next round of branching---possibly by lifting the branch point beyond a putative local inhibitory field. / In summary, we establish that inactivation of PAX8 gene expression does not disturb normal kidney development and function. Conversely, PAX2 plays a crucial dual role in the two primordial kidney cell lineages: being a differentiating factor in mesenchyme and a survival factor in ureteric epithelium.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36844 |
| Date | January 2000 |
| Creators | Torban, Elena. |
| Contributors | Goodyer, Paul (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: 001770403, proquestno: NQ69942, Theses scanned by UMI/ProQuest. |
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