Mutagenesis, Vol. 14, No. 1, 31-36,
January 1999
© 1999 UK Environmental Mutagen Society/Oxford University Press
-Glutamyl transferase (GGT) deficiency in the GGTenu1 mouse results from a single point mutation that leads to a stop codon in the first coding exon of GGT mRNA
The Pulmonary Center, Boston University School of Medicine, 80 East Concord Street, R304, Boston, MA 02118 and 1 Department of Pediatrics, Department of Medical Genetics and The Waisman Center, University of Wisconsin, Madison, WI 53705, USA
GGTenu1, a recently described genetic murine model of 
-glutamyl transferase (GGT) deficiency, was induced by the point mutagen N-ethyl-N-nitrosourea and is inherited as an autosomal recessive trait. The phenotype of systemic GGT deficiency suggested a mutation site within the cDNA coding region which is common in all GGT transcripts. To identify this site, total lung and kidney RNA was isolated from normal and mutant mice, amplified by RT–PCR using GGT-specific primers, cloned as two overlapping ~1 kb GGT cDNA fragments, sequenced and compared with that in the literature. A single base pair substitution was identified in the coding region at position 237, where thymidine became adenine, and this mutation replaced a leucine codon, TTG, with a termination codon, TAG. This mutation site was confirmed in mutant genomic DNA by PCR using primers that flanked the predicted site and spanned the intron between the common GGT non-coding exon and the first GGT coding exon. This PCR product was sequenced directly with the secondary 3' PCR primer, the mutation site identified and the protocol then utilized to genotype animals. In addition to this mutation, the steady-state level of GGT mRNA in mutant kidney is reduced 3-fold compared with the control. Heterodimeric GGT protein is not detectable by western blot in either whole kidney homogenate or a microsomal membrane fraction. The steady-state mRNA level of -glutatmyl cysteinyl synthetase was unchanged in mutant mice compared with normal, but that of heme oxygenase-1 and Cu,Zn-SOD was induced 4- and 3-fold, respectively. Hence, the GGTenu1 mouse model of GGT deficiency results from a single point mutation in the first coding exon of GGT mRNA and the resulting impairment in glutathione turnover induces oxidative stress in the kidney.
2 To whom correspondence should be addressed. Tel: +1 617 638 4860; Fax: +1 617 536 8093; Email: mjbrady{at}bupula.bu.edu
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