Human retroelements may introduce intragenic polyadenylation signals

Area of Science:

• Genomics
• Molecular Biology
• Evolutionary Biology

Background:

• LINE-1 (L1) and Alu retroelements are mobile genetic elements in the human genome.
• These elements can disrupt gene sequences or modulate gene expression.
• Retroelements can introduce regulatory sequences, including polyadenylation signals (pA), into host genes.

Purpose of the Study:

• To investigate the impact of retroelement-derived polyadenylation signals on gene expression.
• To determine if there is an orientation bias of L1 and Alu elements containing pA signals within human genes.
• To understand the evolutionary implications of pA signal insertion by retroelements.

Main Methods:

• Computational analysis of 34 randomly selected human genes from the genome draft sequence.
• Examination of the orientation of L1 and Alu elements relative to host genes.
• Experimental assessment of Alu-based pA sequences in pol II and pol III transcripts.

Main Results:

• A computational analysis revealed an orientation bias: fewer L1 and Alu elements containing pA signals were found in the same orientation as the host gene.
• Experimental studies indicated that Alu-based pA signals are often weak or non-functional in transcripts.
• The surrounding sequence significantly affects pA signal efficiency.

Conclusions:

• The observed orientation bias suggests that even weak influences from retroelement-inserted pA signals exert evolutionary pressure.
• This pressure leads to a non-random distribution of pA-containing L1 and Alu elements within genes.
• The human genome has mechanisms to mitigate the impact of potentially disruptive retroelement insertions.