Position-specific chemical modification of siRNAs reduces "off-target" transcript silencing

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Transfected small interfering RNAs (siRNAs) can regulate unintended transcripts due to limited complementarity.
• This off-target silencing complicates the use of RNA interference (RNAi) for defining gene function.

Purpose of the Study:

• To develop chemical modifications for siRNAs to specifically reduce off-target silencing.
• To investigate the impact of these modifications on both on-target and off-target gene regulation.

Main Methods:

• Introduction of position-specific, sequence-independent chemical modifications into siRNA guide strands.
• Assessment of silencing efficacy against perfectly matched and partially complementary target transcripts.
• Evaluation of off-target phenotypes in cellular growth inhibition studies.

Main Results:

• Chemical modifications significantly reduced the silencing of partially complementary transcripts across all tested siRNAs.
• Silencing of perfectly matched targets remained unaffected by the modifications.
• A key modification, 2 -O-methyl ribosyl substitution at position 2 of the guide strand, specifically reduced silencing of off-target transcripts complementary to the siRNA seed region.
• Off-target phenotypes in growth inhibition assays were also diminished by the chemical modification.

Conclusions:

• Position-specific chemical modifications can effectively mitigate off-target effects of siRNAs.
• The 2 -O-methyl ribosyl substitution at position 2 of the guide strand plays a critical role in reducing off-target silencing, with a distinct mechanism from seed region base-pair substitutions.