Sensitivity of splice sites to antisense oligonucleotides in vivo

A series of HeLa cell lines which stably express beta-globin pre-mRNAs carr ying point mutations at nt 654, 705, or 745 of intron 2 has been developed, The mutations generate aberrant 5' splice sites and activate a common 3' c ryptic splice site upstream leading to aberrantly spliced beta-globin mRNA, Antisense oligonucleotides, which in vivo blocked aberrant splice sites an d restored correct splicing of the pre-mRNA, revealed major differences in the sensitivity of these sites to antisense probes. Although the targeted p re-mRNAs differed only by single point mutations, the effective concentrati ons of the oligonucleotides required for correction of splicing varied up t o 750-fold. The differences among the aberrant 5' splice sites affected sen sitivity of both the 5' and 3' splice sites; in particular, sensitivity of both splice sites was severely reduced by modification of the aberrant 5' s plice sites to the consensus sequence. These results suggest large differen ces in splicing of very similar pre-mRNAs in vivo, They also indicate that antisense oligonucleotides may provide useful tools for studying the intera ctions of splicing machinery with pre-mRNA.