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New CYP1 genes in the frog Xenopus (Silurana) tropicalis: Induction patterns and effects of AHR agonists during development
Ist Teil von
Toxicology and applied pharmacology, 2011-01, Vol.250 (2), p.170-183
Ort / Verlag
Amsterdam: Elsevier Inc
Erscheinungsjahr
2011
Link zum Volltext
Quelle
MEDLINE
Beschreibungen/Notizen
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.