| dc.description.abstract | Measuring changes in gene expression has been established to effectively reflect contaminant-induced changes in physiological mechanisms. Prior research has found that growth-related genes are sensitive endpoints in toxicity tests that use larvae and have potential as endpoints for embryonic organisms. The purpose of this research was to identify the stages of development at which the expression of genetic endpoints that indicate reduced growth potential in fathead minnows is high enough to draw an accurate comparison with contaminant-induced decreases in expression. To accomplish this goal, we evaluated a suite of growth-related genes from embryos and larvae obtained at various 24-hour time points from spawn (Day 0) to Day 11 and quantitatively determined the time points at which expression of these genes was the highest. For the growth-related genes, expression levels of growth hormone (gH) were highest at Days 4-7 and 11, levels of growth hormone receptor (gHR) at Days 1-7 and 11, and levels of insulin-like growth factor (igf1) at Days 4-11. For the thyroid hormone receptors, thyroid hormone receptor-alpha (TR-alpha) showed highest expression levels at Days 3-11 and thyroid hormone receptor-beta (TR-beta) showed highest levels at Days 2-5 and 9. For the deiodinase enzymes, deiodinase-1 (Dio1) expression levels were highest at Days 2-3 and 7-11, levels of deiodinase-2 (Dio2) were highest at Days 7-11, and levels of deiodinase-3 (Dio3) were highest at Days 1-5. The time points associated with highest expression levels amongst these genes may be the most effective points to measure alterations of expression in toxicity testing. | |
