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Atrazine is a commonly used herbicide in the Midwestern United States. Currently, Indiana uses about 26% of its land to grow corn, and atrazine is used in ample amounts, resulting in contamination of drinking water supplies. The U.S. Environmental Protection Agency (EPA) has set the Maximum Contaminant Level (MCL) at 3 parts per billion (ppb) in drinking water, but the herbicide is often found at higher concentrations. However, data suggests that atrazine can cause adverse health impacts even at 3 ppb. Previous studies from our laboratory in the zebrafish model system have shown atrazine alters gene expression associated with neuroendocrine and reproductive system function, carcinogenesis, and cell cycle regulation and an increase in head size following an embryonic atrazine exposure at 0.3, 3, or 30 ppb. From these studies, it was shown that at 72 hours postfertilization (hpf; the end of embryogenesis), atrazine elicits alterations of the gene, tumor protein D52-like 1 (tpd52l1). Previous studies have identified Tpd52l1 in cell proliferation and calcium signaling, along with regulating expression at the G2-M transition in breast cancer cells. The goal of this project was to characterize the expression of tpd52l1 during development of the zebrafish, as well as determine developmental time-point specific gene alterations caused by the embryonic atrazine exposure. To characterize the expression of tpd52l1 throughout embryogenesis, zebrafish embryos were bred and embryos were collected at 24, 36, 48, 60, and 72 hpf for RNA isolation. In addition, alteration in tpd52l1 gene expression following atrazine exposure was assessed at the same developmental time points. Analysis by quantitative polymerase chain reaction (qPCR) showed consistent levels of gene expression throughout embryonic development (p > 0.05), but a significant increase at 36 hpf in the 0.3 and 3 ppb treatments and a significant decrease at 60 hpf was observed in all three atrazine treatments (p < 0.05). T