New CYP1 genes in the frog Xenopus (Silurana) tropicalis: Induction patterns and effects of AHR agonists during development

Abstract

The Xenopus tropicalis genome shows a single gene in each of the four cytochrome P450 1 (CYP1) subfamilies that occur in vertebrates, designated as CYP1A, CYP1B1, CYP1C1, and CYP1D1. We cloned the cDNAs of these genes and examined their expression in untreated tadpoles and in tadpoles exposed to waterborne aryl hydrocarbon receptor agonists, 3,3',4,4',5-pentachlorobiphenyl (PCB126), β-naphthoflavone (βNF), or indigo. We also examined the effects of PCB126 on expression of genes involved in stress response, cell proliferation, thyroid homeostasis, and prostaglandin synthesis. PCB126 induced CYP1A, CYP1B1, and CYP1C1 but had little effect on CYP1D1 (77-, 1.7-, 4.6-and 1.4-fold induction versus the control, respectively). βNF induced CYP1A and CYP1C1 (26-and 2.5-fold), while, under conditions used, indigo tended to induce only CYP1A (1.9-fold). The extent of CYP1 induction by PCB126 and βNF was positively correlated to the number of putative dioxin response elements 0-20 kb upstream of the start codons. No morphological effect was observed in tadpoles exposed to 1 nM-10 µM PCB126 at two days post-fertilization (dpf) and screened 20 days later. However, in 14-dpf tadpoles a slight up-regulation of the genes for PCNA, transthyretin, HSC70, Cu-Zn SOD, and Cox-2 was observed two days after exposure to 1 µM PCB126. This study of the full suite of CYP1 genes in an amphibian species reveals gene-and AHR agonist-specific differences in response, as well as a much lower sensitivity to CYP1 induction and short-term toxicity by PCB126 compared with in fish larvae. The single genes in each CYP1 subfamily may make X. tropicalis a useful model for mechanistic studies of CYP1 functions.

Mixture effects of levonorgestrel and ethinylestradiol: Estrogenic biomarkers and hormone receptor mRNA expression during sexual programming

“…For some genes only the whole transcript sequence has been reported and not sequences for exon-exon junctions. Gene-specific real-time PCR primers for X. tropicalis arnt-2 transcripts were designed by Jönsson et al (2011). To confirm the specificity of the PCR primers the PCR-products were analyzed by melting curve analysis and run on an agarose gel to verify that only one size product was obtained and corresponds to expected size ( Table 2).…”

Liver histology and ultrastructure of the Italian newt (Lissotriton italicus): Normal structure and modifications after acute exposure to nonylphenol ethoxylates

“…In particular, cytochrome P450-1A (CYP-1A) levels have been used as biomarkers of environmental contamination (Buhler and Wang-Buhler, 1998;Gillam and Hunter, 2007); in particular several studies have focused on aryl hydrocarbon receptor-coupled CYP-1A induction (Arukwe et al, 1997;Delescluse et al, 2000;Jönsson et al, 2011). There is a general paucity of information about the activities and expression of CYP-1s in amphibians, despite xenobiotic metabolism in this vertebrate group often reveals different patterns to those seen in mammals (Venturino and Pechen de D'Angelo, 2005;Gillam and Hunter, 2007;Nakayama et al, 2009;Iwamoto et al, 2012).…”

Developmental changes in drug-metabolizing enzyme expression during metamorphosis of <i>Xenopus tropicalis </i>

“…1A). In X. tropicalis, Ahr has been shown to induce expression of CYP1A in response to Ahr agonists such as PCB128 and β-naphthofl avone (Jönsson et al, 2011). Therefore, this increase in ahr mRNA expression during development indicates that CYP1A enzymes are more easily induced in metamorphosed frogs compared with tadpoles.…”