In the antisense process, antisense oligonucleotides (short single-stranded noncoding ribonucleic acids) are introduced into the cell mostly through liposomes (vesicles often consisting of phospholipids). In this process, the mRNA is degraded within a short time.
A cell nucleus introduction of a gene coding for the mRNA by means of vectors (modified plasmid (DNA ring) of a bacterium) is most effective – the synthesis of the antisense RNA takes place continuously in this way.
The actual viral DNA has been modified in such a way that neither replication (duplication) nor transcription (synthesis of RNA using DNA as a template) of the viral genes occurs.
By forming hydrogen bonds, the antisense oligonucleotide binds to the complementary (pre)-mRNA.
Three scenarios may occur:
- The added antisense oligonucleotide is ribonuclease H mediated. In this case, the (pre)-mRNA is cut (i.e., degradation -> loss of function of the mRNA). A translation of the mRNA to the protein thus fails.
- After binding to the mRNA, a so-called steric hindrance occurs. I.e. attachment of cellular proteins – especially ribosomes – is thus no longer possible. The translation to the protein is thus also not possible.
- Influence on splicing (modification process by so-called spliceosome (construct of five different non-coding RNAs called snRNA, to which proteins are bound in each case) as part of RNA processing ((pre)-mRNA to mRNA).Here, so-called. Alternative splicing mechanisms (e.g. intron is not spliced or exon is spliced) can be bypassed and exons can be cut out (= exon skipping; exons are normally left in the mRNA). The antisense oligonucleotide prevents the removal of the exon that is essential for the function of the protein.In other cases to partially correct Raster shift mutations (deletion or insertion, so that the DNA from then on has fundamentally different base triplets, which significantly changes the structure of the protein), the antisense RNA can also cause the cutting out of certain otherwise unspliced RNA segments. Despite thus discretely truncated protein has been “reset” from the site of removal to the reading frame of the mRNA to a non-pathological state.
Therapy
A use of the procedure exists since 2017 in Germany for the therapy of spinal muscular atrophy (SMA), acting on the splicing.
In the United States, the procedure is also used (also with splicing action) for some forms of Duchenne-type muscular dystrophy.
For the sake of completeness, the procedure of inserting a new gene will be discussed: By means of a vector, a gene not present in the DNA is introduced into the nucleus of the cell. This usually codes for a protein in whose gene a mutation was present in the patient and could not fulfill the “desired” function. In 2019, this procedure was approved in the United States for the treatment of spinal muscular atrophy.
