Antisense - RNA, principles and applications
Antisense - RNA:- It is single-stranded RNA molecule that can bind and inhibit specific mRNA translation to protein.
Principle:-
Sense RNA:-
> messenger RNA (mRNA) is single-stranded.
> Its sequence of nucleotides is called "sense" because it results in a gene product (protein).
> Normally, its unpaired nucleotides are "read" by transfer RNA anticodons as the ribosome proceeds to translate the message.
Antisense RNA:-
> RNA can form duplexes just as DNA does.
> All that is needed is a second strand of RNA whose sequence of bases is complementary to the first strand.
> The second strand is called the antisense strand because its sequence of nucleotides is the complement of message sense.
Example:-
5´ C A U G 3´ mRNA
3´ G U A C 5´ Antisense RNA
Antisense technology:-
> When mRNA forms a duplex with a complementary antisense RNA sequence, translation is blocked.
> This may occur because the ribosome cannot gain access to the nucleotides in the mRNA or because the duplex RNA is quickly degraded by ribonucleases in the cell.
.bmp)
> With recombinant DNA methods, synthetic genes (DNA) encoding antisense RNA molecules can be introduced into the organism.
Applications of Antisense technology:-
1. Treatment of viral infection:-
> Antisense oligonucleotides are selective and highly specific and binds with targeted viral mRNA and down regulate the expression of viral proteins, thus inhibit the virus replication.
> Thus this antisense technology can be used to design therapeutic compounds targeted to specific mRNA to treat various viral diseases.
> Vitravene (fomivirsen):- It is the first antiviral Antisense drugs used to treat cytomegalovirus retinitis. Other potential targets of antisense drugs include human papillomavirus, HIV, hepatitis-B virus, influenza A virus, and herpes simplex virus (HSV).
2. Treatment of cancer:-
> As antisense drugs are less toxic than conventional drugs, many antisense oligonucleotides are currently investigated to treat various cancers in humans or for the deactivation of oncogenes.
> For the first time an antisense oligonucleotide in combination with cisplatin was approved to treat bladder cancer.
3. Gene therapy:-
> Antisense oligonucleotides are being used in genetic research to treat various genetic disorders.
> In genetic disorders, some point mutations resulting in the formation of a defective mRNA and then defective protein.
> Antisense oligonucleotides blocks the formation of defective mRNA and then defective proteins.
> β-thalessemia:- A genetic blood disorder can be completely treated using antisense technology in which O-alkyl oligonucleotides or morpholino-oligonucleotides have been used.
4. Medical applications:-
> Antisense technology is used to investigate protein function in the living brain to study central nervous system (CNS) proteins such as transmembrane receptors, ion channels, transporters, G proteins, and growth factors.
> Antisense oligonucleotides can be used to inhibit expression of a particular enzyme. For eg. Inhibition of acetyl cholinesterase enzyme is the molecular target for the treatment of diseases like Alzheimer’s disease.
> In inflammatory diseases, antisense oligonucleotides is used to demonstrate the relative importance of various signaling components at the molecular level.
> A novel respirable antisense drug called RASONS is used to treat various respiratory diseases including asthma, influenza, bronchitis, pulmonary fibrosis, pneumonia, and lung cancer.
> Antisense oligonucleotide can be used target specific membrane component that influences the pathophysiological mechanisms in renal and cardiovascular disorders.
5. Flavr Savr tomatoes:-
> Most tomatoes that have to be shipped to market are harvested before they are ripe. Otherwise, ethylene synthesized by the tomato causes them to ripen and spoil before they reach the customer.
> Transgenic tomatoes have been constructed that carry in their genome an artificial gene (DNA) that is transcribed into an antisense RNA complementary to the mRNA for an enzyme involved in ethylene production. These tomatoes make only 10% of the normal amount of the enzyme.
> The goal of this work was to provide supermarket tomatoes with something closer to the appearance and taste of tomatoes harvested when ripe.