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ToxSci Advance Access published online on August 25, 2004
Toxicological Sciences, doi:10.1093/toxsci/kfh260
Toxicological Sciences © Society of Toxicology 2004; all rights reserved
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Received April 15, 2004
Accepted August 12, 2004

Safety Evaluation

A Cyp1a2-Luciferase Transgenic CD-1 Mouse Model: Responses to Aryl Hydrocarbons Similar to the Humanized AhR Mice

Weisheng Zhang 1*, Bhagavatula Moorthy 2, Min Chen 1, Kathirvel Muthiah 2, Richard Coffee 3, Anthony F. Purchio 1, David B. West 1

1 Xenogen Corporation, 860 Atlantic Avenue, Alameda, California 94501
2 Department of Pediatrics, Baylor College of Medicine, 6621 Fannin, FC 530.01, Houston, Texas 77030
3 Xenogen Biosciences, 5 Cedar Brook Drive, Cranbury, New Jersey 08512

* To whom correspondence should be addressed. E-mail: wzhang{at}xenogen.com.


  Abstract

Here we describe a transgenic mouse model [Crl:CD-1(ICR)BR-Tg(Cyp1a2-luc)Xen] using luciferase as a reporter for Cyp1a2 gene regulation. An 8.4 kilobase mouse Cyp1a2 promoter driving the firefly luciferase gene was microinjected into single cell stage CD-1 mouse embryos. A transgenic mouse line was selected based on basal and induced levels of the transgene in mouse liver by an in vivo bioluminescent imaging method. The basal levels of the luciferase reporter in liver were expressed much higher than other tissues, which correlated well with the endogenous Cyp1a2 mRNA tissue distribution. Male signals were about 23 fold higher than females in liver. However, the Cyp1a2 mRNA showed no gender difference. When mice were challenged with xenobiotics, the liver luciferase signal was induced to various degrees. At the doses we used, the relative effects were phenobarbital > 2,3,7,8-tetrachlorodibenzo-p-dioxin > 3-methylcholanthrene > benzo[a]pyrene and {beta}-naphthoflavone. Induction of the Cyp1a2-luc reporter was generally consistent with the endogenous Cyp1a2 mRNA. However, phenobarbital induction was unexpectedly higher while {beta}-naphthoflavone induction of the reporter was much lower than that of the endogenous Cyp1a2 gene. Induction of the Cyp1a2-luc transgene by aryl hydrocarbons (Ah) in the CD-1 background was much less than that found in the Ah responsive C57BL/6 mice, while being similar to the non-responsive DBA/2 strain. Sequence analysis of the CD-1 Ah receptor (AhR) cDNA clones demonstrated that consensus sequence was identical to some of the Ah responsive strains such as BALB/C and CBA/J mice. The 104 kD AhR protein was not detectable in CD-1 mice while the 97 kD AhR was detected in the C57BL/6 mice by Western blot using an AhR antibody. Low expression of the AhR in CD-1 mice could be in part responsible for low-responsiveness to Ah compounds. The findings demonstrated the out-bred CD-1 mouse is a low responsive strain and the Cyp1a2-luc transgenic CD-1 mice can be used for studying the regulation of the mouse Cyp1a2 gene in an Ah low-responsive strain in real time using the bioluminescent imaging approach.

Keywords: Cytochrome P450 1A2; transgenic mice; aryl hydrocarbon receptor; drug metabolism; xenobiotics; luciferase; reporter; imaging; gene regulation.
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