Structure of the mouse gene encoding CD4 and an unusual transcript in brain

Area of Science:

• Immunology
• Molecular Biology
• Neuroscience

Background:

• The T-cell differentiation antigen CD4 (also known as L3T4 in mice) is crucial for T-cell function in recognizing MHC class II proteins.
• Previous studies suggested evolutionary links between CD4 and immunoglobulin variable regions based on cDNA sequences.
• CD4 gene expression was known in T-lineage cells, but its presence in other tissues was less understood.

Purpose of the Study:

• To investigate the gene structure and expression of mouse CD4 (L3T4), particularly focusing on its unexpected transcription in the brain.
• To determine the structural organization of the L3T4 gene and characterize the shorter transcript found in brain tissue.
• To elucidate the origin and potential protein product of the shorter L3T4 transcript.

Main Methods:

• Gene structure analysis of the L3T4 gene, including exon-intron organization.
• Transcriptional analysis to identify the start site and structure of the shorter L3T4 mRNA in mouse brain.
• Sequence analysis of the shorter transcript to predict the encoded protein.

Main Results:

• The mouse L3T4 gene spans 26 kilobases and comprises 10 exons.
• The L3T4 gene structure resembles other immunoglobulin superfamily members, with a unique intron within the N-terminal homology unit.
• A shorter L3T4 transcript was identified in the brain, originating from a transcriptional start site within exon VI.
• This shorter transcript, if translated, would yield a protein of 217 amino acids, lacking the signal peptide and N-terminal region of the mature protein.

Conclusions:

• The L3T4 gene exhibits a unique structural organization within the immunoglobulin superfamily.
• Alternative transcription initiation in the brain generates a distinct, shorter L3T4 mRNA.
• The shorter brain transcript encodes a truncated protein, suggesting potential tissue-specific functions or regulatory mechanisms for CD4.