Snurps join RNAi toolkit

US researchers have developed synthetic oligonucleotides that may herald a new technique in gene silencing.

The technique is called U1 small nuclear (sn)RNA interference, or U1i, and is based on using U1 snRNAs to form a U1 snRNP (pronounced ‘snurp’) complex and block pre-mRNA polyadenylation.

snRNPs make up the spliceosome in the nucleus, which removes introns from pre-mRNAs. The U1 snRNP is the first to bind the splicing complex.

U1i involves the U1 snRNP complex hybridising to the target gene’s pre-mRNA and inhibiting the formation of a poly(A) tail. Without polyadenylation, the pre-mRNA fails to mature and is degraded in the nucleus.

The team, led by Rutgers University Associate Professor Samuel Gunderson, who described the technique in a paper in PNAS in 2003, say the method has not been widely adopted as there were concerns over specificity and the difficulty in preparing target plasmids.

Now, Gunderson and colleagues have developed synthetic oligos called U1 Adaptors that have dual functions. They have a target domain designed to base pair to the target gene’s pre-mRNA in the three prime terminal exon, and a U1 domain that tethers the U1 snRNP to the target pre-mRNA.

By combining both of these functions, the oligos can inhibit pre-mRNA maturation by cutting off the poly(A) tail step, in a gene-specific manner.

They describe their work online in advance of publication in Nature Biotechnology.

The most common gene silencing method uses short interfering RNA mimics to cleave mRNA. Antisense-mediated gene silencing is also used, with one antisense-based therapeutic now on the market.

Gunderson says potency is increased by using multiple U1 Adaptors to target the same gene or when used in conjunction with siRNAs.

Rutgers University has filed a patent application for the technique and is seeking commercial partners.