dsRNAi

For our final BIOL1040 content lecture, Dr Botella was telling us a bit about the research that he and his group have been involved in over the years. One of the (many) interesting stories he told was of self-vaccinating plants. While the plants must actually be genetically transformed for this to work (they can't do that themselves, at least not voluntarily), once they are transformed with the right DNA sequences, they can provide their own defence against invading parasites. This also has big implications for human/animal immunity, too.

dsRNAi refers to the main molecule used with this method, double stranded DNA (interference). Essentially, when a plant or animal cell detects an unprotected double stranded RNA segment, it cuts up the segment into smaller pieces (small nucleotide repeats/SNPs if I recall correctly) and then separates the double stranded RNA back into single strands again. One strand is then used to remove other RNA copies from the cell (stopping existing transcription) and the other is used to find the gene in the DNA and silence it (generally through methylation of the accompanying histones).
It is possible to artificially stimulate this process by inserting a reversed copy of a gene directly behind the original gene. The RNA produced will thus have two complimentary halves, and will form the double stranded RNA complex, allowing the experimenter to silence the copied gene.

What's more is that if a gene not used by the host organism but crucial to a parasite's survival is inserted along with its reverse, any parasite that feeds on the host's cells will take up the double stranded RNA and its cruicial gene will be silenced. The host thus produces its own vaccine, and the dsRNAi can be transferred between cells as well as produced in any cells that are transformed with the silenced gene. So, as long as the cells can be transformed, any eukaryotic cell can be treated with this vaccine. This means that retroviruses are a key delivery method while plants can be transformed with agrobacterium.

Dr Botella also said that we should see an 'explosion' in medical treatments based on this idea. The reason for the stymied research: two big companies were fighting over the patents, and a US big (insert actual word) attorney has ruled in favour of one company.

There is something potentially quite scary about using this new RNAi system (we need to make a snazzy name for it...): since humans rely upon the correct operation of certain genes to remain living, it would be very easy to use the viral vector method to silence our genes, and we have very little natural defence against it. Is there a method to counter this threat? One benefit of the great mutability of viruses is that they probably would differentiate into non-deadly strains as they mutate. Would we be able to develop resistance to this (and could we demonstrate it in a lab)? Of course, you would need to include the virus replication sequence as well as the gene silencing RNA to be really deadly, and this limits greatly the size of the gene you can knock out. But, perhaps you could use another (retro) virus with just packaging information to infect the host and the host will manufacture the dsRNAi-weapon virus by itself! Before dying, which may be another way to keep us alive (cells die before transmitting virus).

Food (and agrobacteria) for thought,
Josh Harbort