Ahr2-dependance of PCB126 effects on the swim bladder in relation to expression of CYP1 and cox-2 genes in developing zebrafish

Jönsson, M.E., Kubota, A., Timme-Laragy, A., Woodin, B., and Stegeman, J.J.
Toxicology and applied pharmacology   265(2): 166-174 (Journal)
Registered Authors
Stegeman, John J.
zebrafish, swim bladder, aryl hydrocarbon receptor (Ahr), 3,3',4,4',5-pentachlorobiphenyl (PCB126), cytochrome P450 1 (CYP1), cyclooxygenase 2 (Cox-2), embryonic development
MeSH Terms
  • Air Sacs/drug effects*
  • Air Sacs/embryology
  • Air Sacs/enzymology
  • Animals
  • Cyclooxygenase 2/biosynthesis*
  • Cyclooxygenase 2/genetics
  • Cyclooxygenase 2/metabolism
  • Cytochrome P-450 CYP1A1/biosynthesis*
  • Cytochrome P-450 CYP1A1/genetics
  • Cytochrome P-450 CYP1A1/metabolism
  • Dose-Response Relationship, Drug
  • Embryo, Nonmammalian/drug effects
  • Estrogen Antagonists/toxicity*
  • Female
  • Histocytochemistry
  • Male
  • Polychlorinated Biphenyls/toxicity*
  • RNA, Messenger/biosynthesis
  • RNA, Messenger/genetics
  • Real-Time Polymerase Chain Reaction
  • Receptors, Aryl Hydrocarbon/agonists
  • Receptors, Aryl Hydrocarbon/metabolism*
  • Zebrafish
  • Zebrafish Proteins/agonists
  • Zebrafish Proteins/metabolism*
  • beta Catenin/genetics
  • beta Catenin/metabolism
23036320 Full text @ Tox. App. Pharmacol.

The teleost swim bladder is assumed a homolog of the tetrapod lung. Both swim bladder and lung are developmental targets of persistent aryl hydrocarbon receptor (AHR) agonists; in zebrafish (Danio rerio) the swim bladder fails to inflate with exposure to 3,32,4,42,5-pentachlorobiphenyl (PCB126). The mechanism for this effect is unknown, but studies have suggested roles of cytochrome P4501 (CYP1) and cyclooxygenase 2 (Cox-2) in some Ahr-mediated developmental effects in zebrafish. We determined relationships between swim bladder inflation and CYP1 and Cox-2 mRNA expression in PCB126-exposed zebrafish embryos. We also examined effects on β-catenin dependent transcription, histological effects, and Ahr2 dependance of the effect of PCB126 on swim bladder using morpholinos targeting ahr2. One-day-old embryos were exposed to waterborne PCB126 or carrier (DMSO) for 24 h and then held in clean water until day 4, a normal time for swim bladder inflation. The effects of PCB126 were concentration-dependent with EC50 values of 1.4 to 2.0 nM for induction of the CYP1s, 3.7 and 5.1 nM (or higher) for cox-2a and cox-2b induction, and 2.5 nM for inhibition of swim bladder inflation. Histological defects included a compaction of the developing bladder. Ahr2-morpholino treatment rescued the effect of PCB126 (5 nM) on swim bladder inflation and blocked induction of CYP1A, cox-2a, and cox-2b. With 2 nM PCB126 approximately 30% of eleutheroembryos failed to inflate the swim bladder, but there was no difference in CYP1 or cox-2 mRNA expression between those embryos and embryos showing inflated swim bladder. Our results indicate that PCB126 blocks swim bladder inflation via an Ahr2-mediated mechanism. This mechanism seems independent of CYP1 or cox-2 mRNA induction but may involve abnormal development of swim bladder cells.

Genes / Markers
Mutations / Transgenics
Human Disease / Model
Sequence Targeting Reagents
Engineered Foreign Genes