Tissue-specific expression of human CD4 in transgenic mice

Area of Science:

• Molecular Biology
• Immunology
• Genetics

Background:

• The CD4 glycoprotein is essential as the primary receptor for the human immunodeficiency virus type 1 (HIV-1).
• Understanding the regulatory elements controlling CD4 gene expression is critical for insights into HIV-1 infection and potential therapeutic strategies.

Purpose of the Study:

• To identify and characterize the 5' flanking sequences of the human CD4 gene responsible for directing tissue-specific expression.
• To evaluate the functionality of these regulatory regions in both cell culture and transgenic mouse models.

Main Methods:

• Cloning of the human CD4 gene and approximately 23 kb of its upstream sequence.
• Testing the transcriptional activity of different 5' flanking regions (6 kb and 23 kb) in NIH 3T3 cells and the murine T-cell line EL4.
• Generating and analyzing transgenic mice to assess tissue-specific expression patterns of human CD4.
• Utilizing flow cytometry to examine human CD4 protein expression on peripheral blood mononuclear cells.

Main Results:

• A 6 kb 5' flanking region showed transcription in NIH 3T3 cells but lacked expression in EL4 cells and transgenic mice.
• A larger 23 kb 5' flanking region successfully directed high-level CD4 transcription in EL4 cells and three lines of transgenic mice.
• Human CD4 RNA expression in transgenic mice correlated with murine CD4 expression, with highest levels in the thymus and spleen.
• Human CD4 protein was detected on 45-50% of peripheral blood mononuclear cells, specifically on the CD4+ lymphocyte subset.

Conclusions:

• The approximately 23 kb 5' flanking region of the human CD4 gene contains crucial elements for directing appropriate tissue-specific and cell-type-specific expression.
• These findings provide valuable insights into the transcriptional regulation of the CD4 receptor, relevant for HIV-1 research and therapeutic development.