Aquatic Toxicology 78 (2006) 272–283 Up-regulation of the alligator CYP3A77 gene by toxaphene and dexamethasone and its short term effect on plasma testosterone concentrations M.P. Gunderson a,d , S. Kohno b , B. Blumberg c , T. Iguchi b , L.J. Guillette Jr. a,∗ a Department of Zoology, University of Florida, P.O. Box 118525, Gainesville, FL 32611-8525, United States b Center for Integrative Bioscience, National Institute for Basic Biology, Okazaki National Research Institutes, 5-1 Higashiyama Myodaiji, Okazaki 444-8585, Japan c Department of Developmental and Cell Biology, University of California, 2113E McGaugh Hall, Irvine, CA 92697-2300, United States d University of Victoria, Department of Biochemistry and Microbiology, Petch 249/251, P.O. Box 3055 STN CSC, Victoria B.C., Canada V8W 3P6 Received 19 July 2005; received in revised form 25 November 2005; accepted 26 November 2005 Abstract In this study we describe an alligator hepatic CYP3A gene, CYP3A77, which is inducible by dexamethasone and toxaphene. CYP3A plays a broad role in biotransforming both exogenous compounds and endogenous hormones such as testosterone and estradiol. Alligators collected from sites in Florida that are contaminated with organochlorine compounds exhibit differences in sex steroid concentrations. Many organochlorine compounds induce CYP3A expression in other vertebrates; hence, CYP3A induction by organochlorine contaminants could increase biotransformation and clearance of sex steroids by CYP3A and provide a plausible mechanism for the lowering of endogenous sex steroid concentrations in alligator plasma. We used real time PCR to examine whether known and suspected CYP3A inducers (dexamethasone, metyrapone, rifampicin, and toxaphene) up-regulate steady state levels of hepatic CYP3A77 transcript to determine if induction patterns in female juvenile alligators are similar to those reported in other vertebrates and whether toxaphene, an organochlorine compound found in high concentrations in Lake Apopka alligators, induces this gene. Estrogen receptor  (ER), estrogen receptor  (ER), androgen receptor (AR), glucocorticoid receptor (GR), progesterone receptor (PR), and steroid-xenobiotic receptor (SXR) transcripts were also measured to determine whether any of these nuclear receptors are also regulated by these compounds in alligators. Dexamethasone (4.2-fold) and toxaphene (3.5-fold) significantly induced CYP3A77 gene transcript, whereas rifampicin (2.8-fold) and metyrapone (2.1-fold) up-regulated ER after 24 h. None of the compounds significantly up-regulated AR, ER, GR, PR, or SXR over this time period. Plasma testosterone (T) did not change significantly after 24 h in alligators from any of the treatment groups. Dexamethasone treated animals exhibited a strong relationship between the 24 h plasma T concentrations and CYP3A77 (R 2 = 0.9, positive) and SXR (R 2 = 0.77, negative) transcripts, which suggests that the expression of these genes is related to plasma T in alligators. In light of our findings, we hypothesized that higher steady state CYP3A77 (and possibly SXR) gene expression would be observed in alligators collected from Lake Apopka, a polluted lake containing organochlorine compounds known to induce CYP3A isoforms in other taxa. Therefore, we measured basal levels of CYP3A77 and SXR gene transcripts in wild juvenile alligators collected from Orange Lake (reference lake), Lake Woodruff (reference lake), and Lake Apopka (contaminated lake). We found that no differences existed in CYP3A77 or SXR gene expression among animals from the lakes sampled suggesting that exposure to organochlorine compounds at concentrations present in Lake Apopka does not lead to variation in the expression of these genes, although capture stress could be interfering with these results since the glucocorticoid dexamethasone induces CYP3A77 transcript in alligators. © 2006 Elsevier B.V. All rights reserved. Keywords: Metyrapone; Rifampicin; Androgen receptor; Estrogen receptor; Progesterone receptor; Steroid xenobiotic receptor; Pregnane X receptor; Glucocorticoid receptor; Cytochrome P-450 3A; Androgen biotransformation ∗ Corresponding author at: Department of Zoology, University of Florida, P.O. Box 118525, Gainesville, FL 32611-8525, United States. Tel.: +1 352 392 1098. E-mail addresses: mgunders@uvic.ca (M.P. Gunderson), ljg@zoo.ufl.edu (L.J. Guillette Jr.). 1. Introduction Juvenile female alligators inhabiting the Belle Glade area located at the southern end of Lake Okeechobee (FL) exhibit lower plasma testosterone (T) and estradiol-17 (E 2 ) concen- 0166-445X/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.aquatox.2005.11.010