Spontaneous mutations in recombinant inbred mice: mutant toll-like receptor 4 (Tlr4) in BXD29 mice.
Recombinant inbred (RI) mice are frequently used to identify QTL that underlie differences in measurable phenotypes between two inbred strains of mice. Here we show that one RI strain, C57BL/6J x DBA/2J (BXD29), does not develop an inflammatory response following inhalation of LPS. Approximately 25% of F2 mice [F1(BXD29 x DBA/2J) x F1] are also unresponsive to inhaled LPS, suggesting the presence of a recessive mutation in the BXD29 strain. A genomic scan of these F2 mice revealed that unresponsive animals, but not responsive animals, are homozygous for C57BL/6J DNA at a single locus on chromosome 4 close to the genomic location of Tlr4. All progeny between BXD29 and gene-targeted Tlr4-deficient mice are unresponsive to inhaled LPS, suggesting that the mutation in the BXD29 strain is allelic with Tlr4. Moreover, the intact Tlr4 receptor is not displayed on the cell surface of BXD29 macrophages. Finally, a molecular analysis of the Tlr4 gene in BXD29 mice revealed that it is interrupted by a large insertion of repetitive DNA. These findings explain the unresponsiveness of BXD29 mice to LPS and suggest that data from BXD29 mice should not be included when using BXD mice to study phenotypes affected by Tlr4 function. Our results also suggest that the frequency of such unidentified, spontaneously occurring mutations is an issue that should be considered when RI strains are used to identify QTL.
Cook
Donald N
DN
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA. cookd@niehs.nih.gov
Whitehead
Gregory S
GS
Burch
Lauranell H
LH
Berman
Katherine G
KG
Kapadia
Zareen
Z
Wohlford-Lenane
Christine
C
Schwartz
David A
DA
D000280:Administration, Inhalation; D000483:Alleles; D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology / Q000276:immunology; D005808:Genes, Recessive; D007113:Immunity, Innate / Q000235:genetics; D018836:Inflammation Mediators / Q000502:physiology; D008070:Lipopolysaccharides / Q000008:administration & dosage / Q000502:physiology; D008264:Macrophages / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D018345:Mice, Knockout; D009154:Mutation; D011995:Recombination, Genetic; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics; D051197:Toll-Like Receptor 4 / Q000172:deficiency* / Q000235:genetics* / Q000502:physiology
D018836:Inflammation Mediators; D008070:Lipopolysaccharides; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4