Antisense oligodeoxyribonucleotide-directed cleavage of maternal mRNA in Xenopus oocytes and embryos

We have investigated the effect of specific antisense oligodeoxynucleotides (oligos) on endogenous histone H4 mRNA in Xenopus oocytes, eggs and embryos. In unfertilised eggs and non-matured oocytes, one 20-mer oligo (H4-1) mediated the RNAse H-like cleavage of up to 95% of H4 mRNA (which included polysomal mRNA), and cleavage was still obtained when the size of the oligo was reduced to a 10-mer; no cleavage was observed with 6- and 8-mers. The residual uncleaved mRNA appeared to be completely inaccessible to H4-1 since a second injection caused no further cleavage. A second 20-mer (H4-2) directed against a different region of H4 mRNA was much less effective (less than 5% cleavage). In fertilised embryos, injections of H4-1 and an oligo directed against the localised Vg1 mRNA caused less cleavage than in oocytes and also showed signs of inducing localised, non-specific mRNA cleavage. However we have been able to prepare fertilised embryos devoid of Vg1 mRNA by maturing and fertilising oligo-injected oocytes in vitro.