Gene-environment interactions in a mutant mouse kindred with native airway constrictor hyperresponsiveness

Abstract

We mutagenized male BTBR mice with N-ethyl-N-nitrosourea and screened 1315 of their G3 offspring for airway hyperresponsiveness. A phenovariant G3 mouse with exaggerated methacholine bronchoconstrictor response was identified and his progeny bred in a nonspecific-pathogen-free (SPF) facility where sentinels tested positive for minute virus of mice and mouse parvovirus and where softwood bedding was used. The mutant phenotype was inherited through G11 as a single autosomal semidominant mutation with marked gender restriction, with males exhibiting almost full penetrance and very few females phenotypically abnormal. Between G11 and G12, facility infection eradication was undertaken and bedding was changed to hardwood. We could no longer detect airway hyperresponsiveness in more than 37 G12 offspring of 26 hyperresponsive G11 males. Also, we could not identify the mutant phenotype among offspring of hyperresponsive G8-G10 sires rederived into an SPF facility despite 21 attempts. These two observations suggest that both genetic and environmental factors were needed for phenotype expression. We suspect that rederivation into an SPF facility or altered exposure to pathogens or other unidentified substances modified environmental interactions with the mutant allele, and so resulted in disappearance of the hyperresponsive phenotype. Our experience suggests that future searches for genes that confer susceptibility for airway hyperresponsiveness might not be able to identify some genes that confer susceptibility if the searches are performed in SPF facilities. Experimenters are advised to arrange for multigeneration constancy of mouse care in order to clone mutant genes. Indeed, we were not able to map the mutation before losing the phenotype.

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“…Surprisingly, chronic urethane treatment over 6 wks increased tumor number and incidence in resistant B6 mice, resulting in lung tumor multiplicities higher than had been previously reported 11. This increased lung tumor susceptibility could reflect the removal of pathogens from the Jackson Laboratory facilities, which has changed susceptibilities to diseases such as gallstones,32 atherosclerosis,33 colon carcinogenesis,34 and asthma35 in some strains. This increased sensitivity to lung carcinogenesis induced by multiple urethane exposures will aid in evaluating the contribution of expression of specific proteins on lung carcinogenesis, since knock‐out mice are often generated on the B6 background.…”