ANTISENSE RNA | Online Biotech Notes

Online Biotech Notes

ANTISENSE RNA

• Antisense RNA can be defined as a single stranded RNA which is complementary to the messenger RNA, formed within a cell by transcription.

mRNA sequence (sense): UGAAGGUCACCG

Antisense RNA sequence: ACUUCCAGUGGC

• Also referred to as Antisense Transcripts or Antisense Oligonucleotides, these are found in both prokaryotes and eukaryotes.
• Functions: regulation of gene expression, induce DNA methylation by recruiting DNA methyltransferase, block ribosome from binding to mRNA or recruit RNAse H to degrade mRNA and inhibit translation.

ANTISENSE RNA TECHNOLOGY:

• In Antisense RNA technology, an antisense RNA binds with the complementary sense mRNA, thus blocking protein formation by translation. The antisense RNA can be either a synthetic oligonucleotide of less than 30 nucleotides or a longer antisense sequence.
• The idea behind the technology is that when an antisense RNA is introduced into a cell,it specifically binds to the target mRNA by complementary base pairing. This results in formation of RNA dimer in the cytoplasm and thus stops the synthesis of proteins.

The translation of mRNA can be blocked preferably by three mechanisms:

i) The dsRNA prevents ribosomes from binding to the sense RNA and thus halting the translation

ii) The dsRNA cannot be transported from within the nucleus to the cytosol.

iii) The dsRNA is susceptible to endoribonucleases that degrades the dsRNA but not the ssRNA.

Mechanism of Antisense Rna

INSERTION OF ANTISENSE RNA INTO CELLS:

The antisense RNA can be introduced into the cell by the following methods:

1) Endocytosis: 

one of the simplest method to introduce nucleotides into the cell but rather inefficient as it requires long amount of time.

2) Micro-injection: 

very high yielding method as it allows the injection of RNA with high precision.

3) Liposome Encapsulation:

A cationic phospholipid bilayer is formed around the nucleotide sequence so that the resulting liposome can merge with the cell membrane allowing antisense RNA to enter; most effective but expensive method.

4) Electroporation: 

conventional method; a shock is applied to the cell so that the antisense RNA can traverse into the cell.

5) Antisense PG Gene: 

PG enzyme responsible for pectin breakdown which is the building block of cell wall can be disabled by introducing antisense PG gene.

Mechanism of antisense RNA technology

(Adapted from Fred Hutchinson Cancer Research Center)

APPLICATIONS of ANTISENSE RNA TECHNOLOGY:

The applications of the Antisense RNA technology include:

1) FlavrSavr Tomato: Antisense RNA is used against the polygalactouronase enzyme which is responsible for the ripening of the fruit.

2) Transgenic ACMV (resistant cassava plant): used against African cassava mosaic virus ( CMV) which is responsible for causing cassava mosaic disease

3) Fundamental Research:the introduction of antisense oligonucleotides can helpdetermine the role of a specific gene in a physiological process.

4) Therapeutic Application: eg. Formivirsen (first antiviral drug developed against CMW).

PROBLEMS ASSOCIATED WITH THE TECHNOLOGY:

1) Antisense RNA still lack effective design and biological activity.

2) Researches are being carried out to find the most efficient method of administration of antisense nucleotide.

3) aRNA sometimes binds to mRNA that is not its target. It is known to improperly bind to human growth factor.