International Mammalian Genome Society

The 16th International Mouse Genome Conference (2002)


POSTER 2 - GENERATION OF APN.C3H CONGENIC STRAINS TO ISOLATE CHROMOSOMAL DOMAINS CONTAINING QUANTITATIVE TRAIT LOCI AFFECTING CAFFEINE METABOLISM

WL Casley
Centre for Biologics Research, Health Products and Food Branch, Health Canada

Nowakowska M, Markovich Y, Menzies JA
Centre for Biologics Research, Health Products and Food Branch, Health Canada

The APN mouse was derived from an outbred Swiss Webster line and shows decreased capacity for caffeine metabolism relative to other inbred mouse strains. We have previously demonstrated the presence of quantitative trait loci (QTLs) affecting caffeine 3-demethylation on chromosomes 1, 4 and 9, using an APN x C3H/HeJ intercross. In the present study, we have generated three congenic strains to isolate the chromosomal regions containing the QTL alleles from the C3H/HeJ donor onto an APN background. Congenic strains were developed using marker-assisted selection with average marker spacing of 17.5cM. The caffeine 3-demethylation (C 3-D) index phenotype was determined at each generation. After the sixth backcross generation, sibs from each line were inbred to produce animals homozygous for the congenic interval.  These lines are presently in the second generation of inbreeding. The congenic intervals defined for these strains are APN.C3H-(D1Mit495-D1Mit292), APN.C3H-(D4Mit26-D4Mit232) and APN.C3H-(D9Mit196-D9Mit97). Phenotyping of the N6F2 animals for each strain showed that the strains harbouring chromosome 4 or 9 segments maintained an elevated C 3-D index, while the strain harbouring the chromosome 1 segment was indistinguishable from the recipient strain. The congenic segment in the APN.C3H-(D9Mit196-D9Mit97) strain includes the Cyp1a2 locus, which encodes the enzymes primarily responsible for caffeine 3-demethylation. Relative hepatic expression of the Cyp1a2 gene in this strain and the recipient strain was determined by semi-quantitative RT-PCR. We are currently developing strains that are doubly congenic for the chromosome 1 and 9 segments in order to test for epistatic effects between these loci.


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