Male reproductive health is of growing concern, as male toxicant exposure can affect progeny outcome; sperm chromatin structure integrity may be a contributing factor. The formation of mature sperm involves the expression of numerous proteins involved in organizing and packaging the chromatin in a specific manner; this ensures transmission and participation of the paternal genome in embryogenesis. Exposure of male rats to cyclophosphamide as spermatid chromatin is remodeled has an adverse effect on embryo development. The hypothesis of this thesis is that cyclophosphamide exposure causes genetic damage and alters the sperm proteome, thus disrupting components of chromatin condensation and organization during spermiogenesis. The first objective was to assess the phase specificity of the susceptibility of spermiogenic germ cells to cyclophosphamide-induced DNA damage. Spermatozoa were analyzed for DNA strand breaks using the comet assay. Cyclophosphamide-induced DNA damage was dose-related and accumulated over time. Germ cell phase-specific damage was maximal during midspermiogenesis; this reflects an increased susceptibility of step 9-14 spermatids at a key point in sperm chromatin remodeling, the histone-protamine exchange. The second objective was to examine the sperm chromatin structure and basic proteome. Multiple assays demonstrated that the effects of cyclophosphamide on sperm chromatin structure were also germ cell-phase specific; midspermiogenic spermatids were most sensitive. Sperm were less condensed with reduced total thiol and protamine contents. The sperm basic proteome was also altered; identified proteins are involved in a variety of spermiogenic and fertilization events. The nuclear matrix organizes chromatin into loop domains, and various components of somatic cell matrices are targets for chemotherapeutic agents. Therefore the last objective of this study was to assess the effect of cyclophosphamide exposure on the protein profile of the sperm nuclear matrix. The expression of several nuclear matrix protein components, a number of which were identified for the first time, was altered following drug exposure. Together these results show that cyclophosphamide alters male germ cell chromatin remodeling at both the DNA and protein level; this could alter sperm function and thus explain the adverse effects on early embryo development.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.103039 |
| Date | January 2007 |
| Creators | Codrington, Alexis. |
| 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 Pharmacology & Therapeutics.) |
| Rights | © Alexis Codrington, 2007 |
| Relation | alephsysno: 002599021, proquestno: AAINR32344, Theses scanned by UMI/ProQuest. |
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