A SYNTHETIC, CHEMICALLY-MODIFIED RIBOZYME ELIMINATES AMELOGENIN, THE MAJOR TRANSLATION PRODUCT IN DEVELOPING MOUSE ENAMEL IN-VIVO

Ribozymes are small RNA structures capable of cleaving RNA target mole cules in a catalytic fashion. Designed ribozymes can be targeted to sp ecific mRNAs, blocking their expression without affecting normal funct ions of other genes. Because of their specific and catalytic mode of a ction ribozymes are ideal agents for therapeutic interventions against malfunctioning or foreign gene products, Here we report successful ex periments to 'knock out' a major translation product in vivo using syn thesized, chemically modified ribozymes, The ribozymes, designed to cl eave amelogenin mRNA, were injected close to developing mandibular mol ar teeth in newborn mice, resulting in a prolonged and specific arrest of amelogenin synthesis not caused by general toxicity, No carriers w ere required to assist cellular uptake, Amelogenins are highly conserv ed tissue-specific proteins that play a central role in mammalian enam el biomineralization. Ultrastructural analyses of in vivo ribozyme-tre ated teeth demonstrated their failure to develop normally mineralized enamel, These results demonstrate that synthesized ribozymes can be hi ghly effective in achieving both timed and localized 'knock-out' of im portant gene products in vivo, and suggest new possibilities for suppr ession of gene expression for research and therapeutic purposes.