This thesis has examined the association between the expression of a cell adhesion molecule, epithelial-cadherin (E-cadherin), and rat embryo malformations induced by three model teratogens and an E-cadherin antisense oligonucleotide during organogenesis in vitro. The embryo malformations induced by phosphoramide mustard (PAM), an active metabolite of an anticancer drug, cyclophosphamide, were not associated with any change in the expression of E-cadherin. The embryo malformations induced by exposure to the phorbol ester, 12-0-tetradecanoyl-phorbol-13-acetate (TPA), were associated with an increased steady state concentration of E-cadherin mRNA in the embryo, but not in the yolk sac. This increase in E-cadherin mRNA did not seem to be the cause of the embryo malformations. Exposure of embryos to the heavy metal, cadmium chloride, resulted in an increase in the steady state concentration of E-cadherin protein in the yolk sac, but not in the embryo. The timing of this increase would suggest that it may be one of the factors leading to the embryo malformations. An 18-base E-cadherin antisense oligodeoxynucleotide, injected into the amniotic cavity of 5-7 somite stage rat embryo, down regulated the expression of E-cadherin in the yolk sac, and caused specific open anterior neuropore malformations. Together, these data would suggest that E-cadherin expression is regulated in a tissue-specific manner, and that altering the expression of E-cadherin in the yolk sac is associated with embryo malformations.

Cyclophosphamide is a bifunctional alkylating agent. Administration of low doses of cyclophosphamide to male rats produces severe effects on the outcome of their progeny. The studies in this thesis show that one week treatment with cyclophosphamide can produce about 30% post-implantation loss. This indicates that post-testicular spermatozoa are sensitive to alkylating agents. Previous studies have shown that six weeks treatment caused more than 95% post-implantation loss. The effects of cyclophosphamide treatment on rat spermatozoal nuclei in the testis and epididymis were also addressed in this thesis. Rat cauda epididymal spermatozoa collected after one week of cyclophosphamide treatment showed no change in decondensation pattern in vitro; while samples obtained from rats treated for six weeks showed a slowed chromatin elongation and dispersion pattern. Iodoacetamide binding revealed that there was about a 30% decrease in the amount of free sulfhydryls in spermatozoal nuclei from six weeks treated samples, while there was no detectable change in one week treated samples. DNA single strand breakage was detected in one week treated samples only in the presence of proteinase K in the lysis solution, while significant amounts of both DNA single strand breakage and DNA cross-links were detected in six weeks treated samples. Using a DNA synthesis in vitro system, it was found that six weeks treatment decreased spermatozoal template function, while one week treatment did not result in any significant difference in DNA template function when compared with the control. It is proposed that as the mele germ cells undergo the chromatin transition processes, the chromatin is in an open dynamic status, which expresses many vulnerable sites of the genome to aklylating agent. Since there is no DNA repair system, the alkylation of the genome is cumulative and causes severe damage to the germ cell nuclei; this would lead to early embryo death. Furthermore it is hypothesized that

Thesis (Ph. D.)--University OF MICHIGAN.

Thesis (Ph. D.)--University OF MICHIGAN.

Thesis (Ph. D.)--University OF MICHIGAN.

Even at very low concentrations in the environment, mercury (Hg) has the potential to biomagnify in food chains reaching levels of concern in apex predators such as fish-eating seabirds. The aim of this study was to determine the trophic structure and the transfer of total mercury (THg) and methylmercury (MeHg) in a Gulf of St. Lawrence food web using stable nitrogen (delta 15N) and carbon (delta13C) isotope analysis. Since food is the main exposure route to Hg in organisms, I wanted to characterize and compare the diet of top level predator seabirds using traditional and novel techniques. I found that body weight, trophic level and lipid content of organisms were the best predictors of THg and MeHg in this food web. Although the influence of habitat on the overall Hg distribution in the food web was low, I was able to demonstrate an effect within taxonomical groups which indicates that sediments are a source of THg and MeHg in this ecosystem. Several organisms at the base of the food chain were above the MeHg threshold level for the protection of wildlife suggesting a potential threat for upper trophic level predators. Diet composition of seabirds determined using traditional and novel techniques led to similar and complementary results illustrating that these methods can be combined for future studies to monitor prey availability and to predict the exposure of consumers to Hg.

No description available.

No description available.

No description available.

Eighteen polycyclic aromatic hydrocarbons (PAHs) and 2,3,7,8-tetrachlorodibenzo-pdioxin (TCDD) were examined for their potencies to induce ethoxyresorufin-O-deethylase (EROD) activity in primary cultures of White Leghorn chicken (Gallus domesticus), Pekin duck (Anas platyrhynchos), and Greater Scaup (Aythya marila) embryo hepatocytes. Of the 18 PAHs, only eight induced EROD activity. In chicken hepatocytes the rank order of potency of the eight EROD inducing PAHs was BkF ≥ DahA > Ind > BaA ≥ BghiP ≥ Chr ≥ BaP > BNT. A log-log plot of the ECthr plotted against the LD50 (LD50 data from Brunstrom et al., 1991) for BkF, DahA, BaA, and BNT resulted in a good correlation (r2 = 0.898) between EROD-inducing potency and in ovo lethality. The regression line was used to predict LD50 values for Ind, Chr, and BaP. Although the regression line overestimated the LD50 values, the estimated values appear to be within one order of magnitude of their approximate LD50. The rank order of induction potency of the eight EROD-inducing PAHs in duck and scaup hepatocytes was BkF ≥ DahA > BaP ≥ Ind > BghiP ≥ Chr ≥ BaA > BNT, and BkF ≥ DahA > BaP ≥ Ind > BaA ≥ BghiP > Chr, respectively. Among species, there was no clear overall trend in relative sensitivity to EROD induction by individual PAHs. The EROD inducing potency of zebra mussel (Dreissena polymorpha) extracts was investigated in hepatocytes of all three species. The rank order of sensitivity to the extracts was chicken > duck ≥ scaup. While TCDD and several PCBs induce porphyrin accumulation in chicken embryo hepatocytes, none of the PAHs elicited this response. Regardless of the lack of porphyrinogenic effects, the EROD data suggests that primary cultures of avian embryo hepatocytes maybe a useful model for predicting the in ovo toxic potencies of PAHs in avian species.