The Effect of Thimerosal on Gene Expression in Saccharomyces cerevisiae: An Application of Microarray Technology

Thimerosal is a preservative and anti-fungal used in many vaccines which is metabolized to ethylmercury (about 50% by weight) and thiosalicylate (used as an analgesic agent). In 1999, thimerosal was removed from vaccines (or left only in trace amounts) as a public health precaution. In 2007, the average human will receive a concentration of 0.01% thimerosal per vaccine. This is equivalent to 50μg thimerosal per 0.5mL dose. According to the Food and Drug Administration (FDA), the maximum amount of thimerosal that a two-year old, fully-vaccinated child could possibly receive is 106.4μg, which is equivalent to 53.2μg of mercury. This reflects a decrease of approximately 77% from the average 237μg of mercury that a similar child would have received in 2001. The purpose of this study is to examine the effects of thimerosal exposure on gene expression using Saccharomyces cerevisiae (Baker’s yeast) as a model organism. This species of yeast shares about 31% of its genome with humans and is easy to manipulate. Microarray technology will be used in order to assess changes in gene expression of yeast exposed to a 0.01% concentration of thimerosal. Changes in gene expression will be described as induced or repressed from the control condition. Analysis of the microarray slides and changes in gene expression will be assessed using MAGICTool, a program developed by the Genome Consortium for Active Teaching (GCAT). The potential effect of thimerosal on a few select genes will be verified independently through reverse transcriptase polymerase chain reaction (RT-PCR) and gel electrophoresis