Monoallelic expression of the murine gene encoding Toll-like receptor 4

Area of Science:

• Immunology
• Genetics
• Molecular Biology

Background:

• Toll-like receptor 4 (Tlr4) is crucial for innate immunity, mediating responses to lipopolysaccharide (LPS) from Gram-negative bacteria.
• Defects in Tlr4 signaling increase susceptibility to bacterial infections.
• The C3H/HeJ mouse strain possesses a mutated Tlr4 allele, exhibiting altered LPS responsiveness.

Purpose of the Study:

• To investigate the molecular basis for the intermediate lipopolysaccharide (LPS) response observed in F1 mice derived from crosses involving the C3H/HeJ Tlr4 mutant allele.
• To elucidate the regulatory mechanisms governing Tlr4 gene expression in different genetic contexts.

Main Methods:

• Analysis of Tlr4 expression patterns in F1 hybrid mice generated from crosses between responder mice and mice carrying distinct Tlr4 alleles (C3H/HeJ and C57BL/10ScCr).
• Assessment of cellular responses to LPS.
• Evaluation of allelic expression and protein production.

Main Results:

• F1 mice from crosses with C3H/HeJ mice displayed an intermediate LPS response, attributed to monoallelic expression of Tlr4.
• Allele usage of Tlr4 was stably maintained during clonal expansion, similar to allelic exclusion.
• In contrast, Tlr4 deletion on the C57BL/10ScCr allele resulted in ubiquitous TLR4 protein expression in F1 mice.

Conclusions:

• Tlr4 exhibits monoallelic expression in the context of the C3H/HeJ mutation, explaining the intermediate LPS response.
• The expression of the autosomal Tlr4 gene is regulated in a manner analogous to X-chromosome-linked genes.
• These findings reveal novel insights into the complex regulation of innate immune receptor gene expression.