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Spontaneous mutations in recombinant inbred mice: mutant toll-like receptor 4 (Tlr4) in BXD29 mice

Donald N Cook1, Gregory S Whitehead, Lauranell H Burch

  • 1Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA. cookd@niehs.nih.gov

Genetics
|December 3, 2005
PubMed

Insights

The BXD29 recombinant inbred mouse strain has a mutation in Toll-like receptor 4 (Tlr4), causing unresponsiveness to lipopolysaccharide (LPS). This finding impacts QTL studies using this strain and highlights mutation frequency concerns in RI mouse research.

Area of Science:

  • Immunology
  • Genetics
  • Mouse Models

Background:

  • Recombinant inbred (RI) mice are crucial for mapping quantitative trait loci (QTL) underlying phenotypic differences between mouse strains.
  • The C57BL/6J x DBA/2J (BXD29) RI strain exhibits an unexpected lack of inflammatory response to inhaled lipopolysaccharide (LPS).

Purpose of the Study:

  • To investigate the genetic basis of LPS unresponsiveness in the BXD29 RI mouse strain.
  • To determine if the observed unresponsiveness is linked to the Toll-like receptor 4 (Tlr4) gene.

Main Methods:

  • Crossbreeding of BXD29 mice with F2 generation mice and Tlr4-deficient mice.
  • Genomic scanning of F2 mice to identify homozygous C57BL/6J DNA loci.
  • Flow cytometry analysis of Tlr4 receptor expression on BXD29 macrophages.
  • Molecular analysis of the Tlr4 gene in BXD29 mice.

Main Results:

  • A recessive mutation causing LPS unresponsiveness in BXD29 mice was mapped to a locus on chromosome 4, near Tlr4.
  • Progeny of BXD29 and Tlr4-deficient mice were uniformly unresponsive to LPS, confirming allelism with Tlr4.
  • BXD29 macrophages lacked surface expression of the Tlr4 receptor.
  • Molecular analysis revealed a large repetitive DNA insertion interrupting the Tlr4 gene in BXD29 mice.

Conclusions:

  • The BXD29 strain harbors a functional mutation in Tlr4, explaining its LPS unresponsiveness.
  • Data from BXD29 mice should be excluded from QTL analyses involving Tlr4-dependent phenotypes.
  • The prevalence of spontaneous mutations in RI strains requires consideration during QTL mapping studies.

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