The dystrophin associated protein (DAP) complex has been implicated in such basic physiological processes as the maintenance of cellular homeostasis, the assembly of basement membranes (BM), and synaptogenesis. The dystroglycans, alpha and beta, constitute the functional core of the DAP complex since they establish the transmembrane link between dystrophin, whose mutations lead to Duchenne (DMD) or Becker (BMD) muscular dystrophy, and the extracellular matrix (ECM). The alpha and beta subunits of dystroglycan result from posttranslational processing of a single propeptide encoded by DAG1. No clinical cases or animal models have been identified with spontaneous mutations in that gene. Therefore, to gain insight to the function of dystroglycans I have used gene targeting to disrupt the coding sequence of Dag1 in murine embryonic stem (ES) cells. We find that dystroglycans are critical in the early stages of development and that a null mutation in Dag1 results in embryonic lethality at embryonic day (E) 6.5 because of a disruption in Reichert's BM. In culture however, the absence of dystroglycan in ES cells targeted for both Dag1 alleles does not obviously hinder their developmental potential. Consequently, I reasoned that it might be possible to circumvent the early lethality observed in 'classical' knockout mice, by injecting Dag1-null ES cells into wild-type blastocysts to generate chimeric mice only partially devoid of dystroglycan. Several chimeric mice developed to maturity and Dag1 -null ES cells were found to contribute extensively to the hindlimb musculature thus allowing the analysis of dystroglycan depleted muscles. These muscles are severely dystrophic, have low levels of dystrophin and a disrupted residual DAP complex, but have apparently normal BMs. Chimeric muscles also have disrupted neuromuscular junctions. In culture, myotubes derived from Dag1-null ES cells form clusters of acetylcholine receptors (AChRs) but these occupy a surface area three time
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36900 |
| Date | January 2001 |
| Creators | Côté, Patrice D. |
| Contributors | Carbonetto, Salvatore (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 Neuroscience.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001802061, proquestno: NQ69993, Theses scanned by UMI/ProQuest. |
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