DNA methylation is an epigenetic phenomenon catalysed by a family of DNA methyltransferases (DNMTs) and is tightly regulated throughout spermatogenesis. In these studies, I employed pharmacological and genetic means to disrupt DNA methylation in the male germ line. First, to lower levels of DNMT activity, I treated adult wild-type (Dnmt1+/+) and DNMT-deficient (Dnmt1c/+) male mice with the anticancer agent 5-aza-2'-deoxycytidine (5-azaCdR), which incorporates into DNA and inhibits methylation. Dnmt1+/+ males treated with clinical doses of 5-azaCdR for 7 weeks, to expose germ cells throughout their development, exhibit abnormal testicular histology, as well as dose-dependent reductions in testis weight, sperm count, fertility, and sperm motility. In contrast, Dnmt1c /+ males are evidently partially protected from the deleterious effects of 5-azaCdR, likely because of lowered levels of DNMT1. Although 5-azaCdR-treated Dnmt1c/+ males display reduced testis weight, they do not have altered sperm number or testicular histology; these males also have greater changes in sperm DNA methylation relative to treated Dnmt1+/+ males. Interestingly, elevated preimplantation loss is observed in females mated with treated males of either genotype. This preimplantation loss appears to result from a reduction in oocyte fertilisation, perhaps because of altered sperm motility. Moreover, higher levels of blastocyst loss were observed in embryos derived from matings with treated Dnmt1 +/+ males. I suggest that the testicular effects and reduced fertility of treated Dnmt1+/+ males are the result of both the cytotoxic and hypomethylating effects of 5-azaCdR, whereas the changes observed in 5-azaCdR-treated Dntnt1c /+ males may be due more to hypomethylation and its consequences. / Our second genetic model targetted the methyl supply necessary for DNA methylation. Methylenetetrahydrofolate reductase (MTHFR) is integral to the folate pathway and is necessary for methionine and S-adenosylmethionine formation; levels of MTHFR are highest in the testis, which suggests a role for this enzyme in spermatogenesis. Indeed, severe MTHFR deficiency (Mthfr -/-) results in severely abnormal spermatogenesis and infertility. Within my studies, I showed that maternal administration of betaine, an alternative methyl donor, throughout gestation and nursing, results in reduced germ cell apoptosis in male pups soon after birth. When betaine supplementation is maintained post-weaning, spermatogenesis is partially restored and fertility increases significantly. Here, I provide evidence that perturbation of the components of the DNA methylation pathway detrimentally affects male germ cell development and fertility.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.85923 |
| Date | January 2005 |
| Creators | Kelly, Tamara Lee Jocelyn |
| 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 Human Genetics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002261409, proquestno: AAINR21660, Theses scanned by UMI/ProQuest. |
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