How do antisense oligonucleotides work in gene silencing?

Antisense oligonucleotides are synthetic fragments of single-stranded DNA or RNA, generally 13-25 nucleotides long, that can bind to complementary target messenger RNA (mRNA) and inactivate it. Once mRNA is bound to the antisense oligonucleotides, the gene expression can be repressed either by degrading the mRNA molecule using RNase H or by blocking the translation of mRNA. The majority of antisense drugs employ the RNase H dependent mechanism, because it can efficiently decrease the mRNA expression by approximately 80% to 95%.