Document Type

Thesis

Date of Award

5-2006

School/College

College of Science, Engineering, and Technology (COSET)

Degree Name

MS in Biology

First Advisor

Associate Professor Desiree A. Jackson

Abstract

The purpose of this study was to examine the effect of arsenic exposure during gestation on the expression of specific marker genes associated with cell proliferation and oxidative stress. Arsenic is a naturally occurring substance that can be found in soil and / water. Drinking water is the primary source of arsenic exposure, via underground wells or rainwater. A potential source of arsenic in our environment is a byproduct of copper smelting arsenic occurs naturally in copper ores. Both the experimental as well as epidemiological evidence suggests that arsenic exposure is a risk factor for various human diseases including cancer. Previous studies have shown that arsenic crosses the placenta and is also found in breast milk [25]. Arsenic exposure may therefore pose a potential risk to the fetus during gestation and after birth by altering gene expression. The hypothesis of this study is that the effects of pre-natal exposure to arsenic may alter gene expression patterns in the brain of fetal rats. To test this hypothesis, 1 2 pregnant Hsd rats were exposed to 200ppm-sodium arsenate ad libitum via drinking water (Experimental Group) from gestational day seven through gestational day twentyone. The control group was given untreated water ad libitum for the same time frame. Brain tissue was harvested and RNA was extracted. Gene expression was measured in the extracted RNA by utilizing Real Time Quantitative Reverse Transcriptasc-Polymerase Chain Reaction (qRT-PCR). The genes studied were: Bax (which is involved in apoptotic cell death), BcZ2 (an anti-apoptotic protein), PCNA (a cell proliferation marker), Cyclinl)l (cell cycle regulatory protein), and MnSOD (associated with stress responses). Beta-Actin (a house keeping gene) was used to normalize the data collected in the form of threshold cycle numbers (Ct values). To measure the relative expression of the genes being studied, the Ct values were compared to the controls utilizing a Student's T-test. The expression of MnSOD was up regulated by 18.5 percent; Cyclin Dl was up regulated by 8.5 percent; PCNA was up regulated by 12 percent and Bax was up regulated by 11 percent. The expression of BcZ-2 was down regulated by 1.2 percent, which was expected since Bax and BcZ-2 work antagonistically in apoptosis. The results of this study indicate that chronic pre-natal exposure to arsenic may cause early cell proliferation, oxidative stress, and premature apoptosis in fetal rat brain evidenced by increases in the expression of PCNA, MnSOD, Bax, cyclin Dland the down regulation of BcZ-2.

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