Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on zebrafish caudal fin regeneration

2, 3, 7, 8-tetrachlorodibenzo p-dioxin (TCDD) is a lipophilic environmental contaminant with a long half-life. TCDD exposure leads chloracne, immunotoxicity, hepatotoxicity and cancer in both mammals and humans. Zebrafish are one of the few vertebrates with the ability to regenerate an organ and can regenerate their caudal fin following partial amputation. This is a well-orchestrated process involving the regeneration of blood vessels, bony rays, nerves and tissue. Therefore, my thesis project focused on using zebrafish fin regeneration as a model to help understand the mechanisms of TCDD toxicity.; Injection of TCDD in adult zebrafish resulted in a dose dependent inhibition of fin regeneration. TCDD exposure resulted in inhibition of fin regrowth that was independent of the stage of regeneration in which it was administered. Due to the systemic nature of the TCDD exposure in these studies, TCDD mediated pathology in multiple organs other than the fin could lead to inhibition of fin regeneration. Therefore, histopathology in zebrafish organs was examined following acute exposure to TCDD. Histopathologic changes were evident in zebrafish liver and gills, however, it is unlikely that the histopathology in these organs completely explains the inhibition of fin regeneration. Levels of CYP1A protein can be used as a biomarker to follow TCDD mediated activation of the aryl hydrocarbon receptor (AHR) pathway. Changes in CYP1A levels were determined immunohistochemically and increased levels of CYP1A protein were correlated with TCDD induced toxicity.; Fin regeneration involves cellular differentiation to form fin structures including blood vessels, cartilage and nerves. Transgenic zebrafish with fluorescent blood vessels were used to examine TCDD mediated changes in angiogenesis and markers for collagen and nerve development were used to follow cellular differentiation. TCDD exposure resulted in altered angiogenesis, however cellular differentiation proceeded normally. While the AHR pathway is important in TCDD toxicity, the pathway has not been fully characterized in zebrafish. Zebrafish AHR and ARNT genes have been cloned and characterized, however, zfAIP had not been characterized. The zfAIP gene was cloned from zebrafish and CYP1A activity was used to characterize the gene. While the mechanism of TCDD toxicity remains to be determined, zebrafish caudal fin regeneration is a useful model for studying TCDD toxicity.