Using reporter gene assays to identify cis regulatory differences between humans and chimpanzees

Area of Science:

• Comparative genomics
• Human and chimpanzee evolution
• Gene regulation

Background:

• Phenotypic divergence between humans and chimpanzees is largely attributed to gene regulation differences.
• Few specific regulatory nucleotide differences between humans and chimpanzees have been identified to date.
• Understanding cis-regulatory element evolution is crucial for explaining species-specific traits.

Purpose of the Study:

• To identify cis-regulatory differences in genes with known differential expression between humans and chimpanzees.
• To functionally validate the impact of these regulatory differences on gene expression.
• To pinpoint specific nucleotides responsible for cis-regulatory divergence.

Main Methods:

• Reporter gene assays were designed for putative human and chimpanzee promoters of 10 differentially expressed genes.
• Promoter activity was tested in human liver cell lines.
• Site-directed mutagenesis was used to investigate specific nucleotide effects on promoter activity.

Main Results:

• Seven out of 10 tested promoters were active in human liver cells.
• Four of these active promoters showed significantly different activity between human and chimpanzee versions.
• Three genes exhibited promoter activity differences that recapitulated known species-specific expression patterns, demonstrating cis-regulatory influence.

Conclusions:

• Changes in cis-regulatory elements significantly contribute to gene expression differences between humans and chimpanzees.
• Specific nucleotide changes, as shown for the DDA3 gene promoter, can drive these regulatory differences.
• This reporter assay approach offers a scalable method for mapping regulatory element divergence.