Defective E beta expression in three mouse H-2 haplotypes results from aberrant RNA splicing

Area of Science:

• Immunogenetics
• Molecular Biology
• Gene Expression

Background:

• Mouse major histocompatibility complex (MHC) class II molecules, including E beta, are crucial for immune responses.
• Defective expression of E beta genes in specific haplotypes (H-2w17, H-2q, H-2f) leads to a lack of E beta protein.

Purpose of the Study:

• To investigate the molecular basis of defective E beta gene expression in H-2w17, H-2q, and H-2f mouse haplotypes.
• To determine if the defect lies in gene transcription or RNA processing.

Main Methods:

• Nuclear run-on transcription assays to assess E beta gene transcription rates.
• S1 nuclease digestion assays to analyze RNA processing and splicing.
• Northern blot analyses to quantify E beta RNA levels.

Main Results:

• E beta gene transcription was found to be normal across all three defective haplotypes.
• Reduced levels of E beta RNA (both normal and aberrant sizes) were observed in w17 and q haplotypes.
• The f haplotype showed even lower E beta RNA levels.
• A single nucleotide insertion in the E beta w17 5' splice site caused aberrant splicing, leading to non-translatable RNA.
• The E beta q defect was similar to E beta w17, while the f haplotype defect resulted in more severe RNA processing issues.

Conclusions:

• The absence of E beta protein synthesis in the studied haplotypes is due to defects in RNA processing, not transcription.
• Two distinct RNA processing defects underlie the lack of E beta protein in these haplotypes.
• Aberrant splicing and premature stop codons prevent the production of functional E beta protein.