Antisense RNA-Technology

What is antisense RNA??

• Antisense RNA is a single-stranded RNA that is complementary to a messenger RNA (mRNA) strand transcribed within a cell.

• They are introduced in a cell to inhibit the translation machinery by base pairing with the sense RNA and activating the RNase H, to develop a particular novel transgenic.

mRNA sequence(sense) Antisense RNA UACUUUGGGCAC

AUGAAACCCGUG

How it Differ from RNAi ??

• The intended effect of the both technique is same but the processing is a little bit different in both.

• Antisense technology degrade the mRNA by RNaseH while RNAi employed enzyme Dicer for degradation.

• RNAi are twice larger than antisense oligonucleotide.

Nature’s Antisense System

• There is a HOK (host killing)/SOK(suppress killing) system of postsegregational killing employed by R1 plasmid in E.Coli.

• When E.Coli cell undergo cell division the daughter cell inherit the hok toxin gene and sok gene from the parents but due to the short half life the sok gets degraded quickly. So in a normal cell hok protein get over expressed and cell die. But if the cell inherit a R1 plasmid which has a sok gene and sok specific promoter to transcribe sok gene then sok over expressed the hok and base pairing with hok it inhibit the translation of hok protein

Flavr-Savr• Flavr-Savr the first FDA approved GM food developed by

Calgene in 1992.• Licensed in may 17, 1994.• Ripening of tomato causes production of an enzyme

Polygalactourodase in a gradual increasing level, which is responsible for softening of the tomato and which becomes the cause of rottening.

• So, tomato never last for few extra days in ripening condition without rottening. Calgene introduced a gene in plant which synthesize a complementary mRNA to PG gene and inhibiting the synthesis of PG enzyme.

The mechanism of inhibiting the translation.

INDIAN CONTRIBUTION

• NIPGR, (National institute of Plant Genome Research) in feb,2010 has developed a tomato by antisense technology which can last long upto 45 days. So no need to pick up the green tomatoes and forcefully ripen them with ethylene and no longer to take tension whether they are going to reach the market shelves or no need hurry up in your kitchen before they go meshy.

• NIPGR scientist had silenced the expression of two important gene which are responsible for loss in firmness and textures during ripening.

The two gene silenced are alpha-man and beta-hex of Glycosyl hydrolase, a kind of enzyme that breaks the chemical bond holding a sugar to either another sugar or some other molecule, like a protein.

Antisense Therapy• Antisense therapy is a mode of treatment for genetic

disorder or infections.• A complementary mRNA strand is synthesized on the

basis of the known pathogenic sequence, and which switch ‘off’ the pathogenic gene by activating the degrading enzyme RNase H.

• Antisense drugs are being researched to treat cancers, HIV, CMV etc.

• Formivirsen is the first antisense antiviral drug developed to treat CMV. It was licensed by FDA in Aug, 1998.

• It is a synthetic 21 member oligonucleotide with phosphorothioate linkages (which are resistant to degradation by nucleases) and has the sequence:

5'-GCG TTT GCT CTT CTT CTT GCG-3‘

Cancer – In 2006 a German physician reported the dose escalation of AP compound can be helpful in curing cancer. Is an antisense to the growth factor TGF-beta2

HIV – In feb,2010 Researcher reported successful reducing the viral load of HIV by developing modified T-Cell, which is antisense to the HIV envelope protein.

Challenges to antisense technology…

1. One major challenge to antisense technology (and RNAi) is the difficulty of getting it into the body. Delivery of the treatment to the brain, for use in diseases like HD, is especially challenging because it must cross the blood-brain barrier.

2. The second major challenge to antisense technology is its inevitable toxic effects. Although antisense technology is engineered to be very specific, it can still cause unintended damage because it would regulate both the mutant and normal Huntington alleles.

CONCLUSION…

The Antisense RNA technology shows the potential for diverse applications to basic research and therapy. antisense technology offers almost unlimited scope for the development of new methods of drug design and one of the most approved approaches among several others, for inactivating a single chosen gene. However, the full commitment of this promise is yet to be established.

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