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Abstract

The inhibitory effect of short antisense oligodeoxynucleotides (aODNs) on cRNA expression in Xenopus oocytes was measured using an electrophysiological assay based on subunit-specific block of cloned alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate receptors. The effect of both phosphorothioate-modified (PS) and phosphodiester (PO) aODNs was strongly length dependent with a half-maximal inhibition calculated for an oligo length of 7.6 nucleotides (nt) and 9.9 nt, respectively. More than 95% inhibition was mediated by a PS aODN of 12 nt and by PO aODNs > or = 15 nt. At a given length PS and PO aODNs showed differential dependence of their inhibitory effect on the injected aODN concentration (half-maximal inhibition at 18 ng/microliter for a PO 12-mer and at 0.19 ng/microliter for a PS 12-mer) and differential saturation behavior. The inhibitory effect of aODNs, even as short as 8 nt for PS oligomers, was highly sequence specific, but almost independent of the position of the respective target site on the cRNA (for PS 8-mers, > or = 70% expression inhibition throughout the tested target sites from the translation initiation to the 3'-untranslated region). Thus, short PS aODNs can be reliably used in order to specifically inhibit protein expression in experiments addressing physiological, molecular biological, and perhaps even therapeutical issues.