A process is provided of introducing an RNA into a living cell to inhibit gene expression of a target gene in that cell. The process may be practiced ex vivo or in vivo. The RNA has a region with double-stranded structure. Inhibition is sequence-specific in that the nucleotide sequences of the duplex region of the RNA and of a portion of the target gene are identical. The present invention is distinguished from prior art interference in gene expression by antisense or triple-strand methods.

Genetic Inhibition by Double-Stranded RNA

Double-stranded RNA (dsRNA) induces sequence-specific post-transcriptional gene silencing in many organisms by a process known as RNA interference (RNAi). Using a Drosophila in vitro system, we demonstrate that 19-23 nt short RNA fragments are the sequence-specific mediators of RNAi. The short interfering RNAs (siRNAs) are generated by an RNase III-like processing reaction from long dsRNA. Chemically synthesized siRNA duplexes with overhanging 3′ ends mediate efficient target RNA cleavage in the lysate, and the cleavage site is located near the center of the region spanned by the guiding siRNA. Furthermore, we provide evidence that the direction of dsRNA processing determines whether sense or antisense target RNA can be cleaved by the produced siRNP complex.

Rna interference mediating small rna molecules

The present invention relates to a Drosophila in vitro system which was used to demonstrate that dsRNA is processed to RNA segments 21-23 nucleotides (nt) in length. Furthermore, when these 21-23 nt fragments are purified and added back to Drosophila extracts, they mediate RNA interference in the absence of long dsRNA. Thus, these 21-23 nt fragments are the sequence-specific mediators of RNA degradation. A molecular signal, which may be their specific length, must be present in these 21-23 nt fragments to recruit cellular factors involved in RNAi. This present invention encompasses these 21-23 nt fragments and their use for specifically inactivating gene function. The use of these fragments (or chemically synthesized oligonucleotides of the same or similar nature) enables the targeting of specific mRNAs for degradation in mammalian cells, where the use of long dsRNAs to elicit RNAi is usually not practical, presumably because of the deleterious effects of the interferon response. This specific targeting of a particular gene function is useful in functional genomic and therapeutic applications.

Rna sequence-specific mediators of rna interference

We describe here a new method for highly efficient detection of microRNAs by northern blot analysis using LNA (locked nucleic acid)-modified oligonucleotides. In order to exploit the improved hybridization properties of LNA with their target RNA molecules, we designed several LNA-modified oligonucleotide probes for detection of different microRNAs in animals and plants. By modifying DNA oligonucleotides with LNAs using a design, in which every third nucleotide position was substituted by LNA, we could use the probes in northern blot analysis employing standard end-labelling techniques and hybridization conditions. The sensitivity in detecting mature microRNAs by northern blots was increased by at least 10-fold compared to DNA probes, while simultaneously being highly specific, as demonstrated by the use of different single and double mismatched LNA probes. Besides being highly efficient as northern probes, the same LNA-modified oligonucleotide probes would also be useful for miRNA in situ hybridization and miRNA expression profiling by LNA oligonucleotide microarrays.

Sensitive and specific detection of microRNAs by northern blot analysis using LNA-modified oligonucleotide probes

Methods and means are provided for reducing the phenotypic expression of a nucleic acid of interest in eucaryotic cells, particularly in plant cells, by introducing chimeric genes encoding sense and antisense RNA molecules directed towards the target nucleic acid, which are capable of forming a double stranded RNA region by base-pairing between the regions with sense and antisense nucleotide sequence or by introducing the RNA molecules themselves. Preferably, the RNA molecules comprises simultaneously both sense and antisense nucleotide sequence.

Methods and means for obtaining modified phenotypes

A novel efficient method for the synthesis of locked nucleic acid (LNA) monomers is described. The LNA 5‘,3‘-diols containing thymine, 4-N-acetyl- and 4-N-benzoylcytosine, 6-N-benzoyladenine, and 2-N-isobutyrylguanine as nucleobases were prepared via convergent syntheses. The method is based on the use of the common sugar intermediate 1,2-di-O-acetyl-3-O-benzyl-4-C-methanesulfonoxymethyl-5-O-methanesulfonyl-d-erythro-pentofuranose (8) that easily can be prepared from d-glucose in multigram scale. Four different nucleobases were stereoselectively coupled to 8 using a modified Vorbruggen procedure to give the corresponding 4‘-C-branched nucleoside derivatives. Subsequent ring closing furnished the protected LNA nucleosides. The 5‘-O-mesyl groups were efficiently displaced by nucleophilic substitution using sodium benzoate. Saponification of the 5‘-benzoates followed by catalytic removal of the 3‘-O-benzyl groups afforded the free LNA diols. The exocyclic amino groups of adenosine and cytidine were selective...

A simplified and efficient route to 2'-O, 4'-C-methylene-linked bicyclic ribonucleosides (locked nucleic acid).

A synthesis of [2.2.1]bicyclo nucleosides which is shorter and provides higher overall yields proceeds via the key intermediate of the general formula III, wherein R 4 and R 5 are, for instance, sulfonates and R 7 is, for instance, a halogen or an acetate. From compounds of the general formula II, such as 3-O-aryl-4-C-hydroxymethyl-1,2-O-isopropylidene-α-D-ribofuranose, intermediates of the general formula III are suitable for coupling with silylated nucleobases. Upon one-pot base-induced ring-closure and desulfonation of the formed [2.2.1]bicyclo nucleoside, a short route to each the LNA (Locked Nucleic Acid) derivatives of adenosine, cytosine, uridine, thymidine and guanidine is demonstrated. The use of the 5′-sulfonated ring-closed intermediate also allows for synthesis of 5′-amino- and thio-LNAs.

Synthesis of [2.2.1]bicyclo nucleosides

A synthesis of [2.2.1]bicyclo nucleosides which is shorter and provides higher overall yields proceeds via the key intermediate of general formula (III), wherein R4 and R5 are, for instance, sulfonates and R7 is, for instance, a halogen or an acetate. From compounds in general formula (II), such as 3-O-aryl-4-C-hydroxymethyl-1,2-O- isopropylidene-α-D-ribofuranose, intermediates of general formula (III) are suitable for coupling with silylated nucleobases. Upon one-pot base-induced ring-closure and desulfonation of the formed [2.2.1]bicyclo nucleoside, a short route to each the LNA (Locked Nucleic Acid) derivatives of adenosine, cytosine, uridine, thymidine and guanidine is demonstrated. The use of the 5'-sulfonated ring-closed intermediate also allows for synthesis of 5'-amino- and thio-LNAs.

Improved synthesis of [2.2.1]bicyclo nucleosides

The 3′-C-allyl furanose 4 has been used as a precursor for synthesis of the novel 2′-O,3′-C-linked bicyclic thymine nucleosides 15, 16, 20 and 25. The three bicyclic β-nucleosides 15, 20 and 25 have been incorporated into oligodeoxynucleotides. One of these nucleosides, dioxabicyclo[3.3.0]octane derivative 25, induces increased thermal stability of duplexes towards complementary RNA.

Henrik M. Pfundheller

Papers

A simplified and efficient route to 2'-O, 4'-C-methylene-linked bicyclic ribonucleosides (locked nucleic acid).

Synthesis of [2.2.1]bicyclo nucleosides

Improved synthesis of [2.2.1]bicyclo nucleosides

Synthesis of 2'-o,3'-c-linked bicyclic nucleosides and bicyclic oligonucleotides

A novel class of conformationally restricted oligonucleotide analogues: synthesis of 2',3'-bridged monomers and RNA-selective hybridisation