Mouse background genetics in biomedical research: The devil's in the details

Background Genetically modified mice are used widely to explore mechanisms in most biomedical fields—including transfusion. Concluding that a gene modification is responsible for a phenotypic change assumes no other differences between the gene‐modified and wild‐type mice besides the targetted gene. Study Design and Methods To test the hypothesis that the N‐terminus of Band3, which regulates metabolism, affects RBC storage biology, RBCs from mice with a modified N‐terminus of Band3 were stored under simulated blood bank conditions. All strains of mice were generated with the same initial embryonic stem cells from 129 mice and each strain was backcrossed with C57BL/6 (B6) mice. Both 24‐h recoveries post‐transfusion and metabolomics were determined for stored RBCs. Genetic profiles of mice were assessed by a high‐resolution SNP array. Results RBCs from mice with a mutated Band3 N‐terminus had increased lipid oxidation and worse 24‐h recoveries, “demonstrating” that Band3 regulates oxidative injury during RBC storage. However, SNP analysis demonstrated variable inheritance of 129 genetic elements between strains. Controlled interbreeding experiments demonstrated that the changes in lipid oxidation and some of the decreased 24‐hr recovery were caused by inheritance of a region of chromosome 1 of 129 origin, and not due to the modification of Band 3. SNP genotyping of a panel of commonly used commercially available KO mice showed considerable 129 contamination, despite wild‐type B6 mice being listed as the correct control. Discussion Thousands of articles published each year use gene‐modified mice, yet genetic background issues are rarely considered. Assessment of such issues are not, but should become, routine norms of murine experimentation.